Patch series "kexec/fadump: remove dependency with CONFIG_KEXEC and
reuse crashkernel parameter for fadump", v4.

Traditionally, kdump is used to save vmcore in case of a crash.  Some
architectures like powerpc can save vmcore using architecture specific
support instead of kexec/kdump mechanism.  Such architecture specific
support also needs to reserve memory, to be used by dump capture kernel.
crashkernel parameter can be a reused, for memory reservation, by such
architecture specific infrastructure.

This patchset removes dependency with CONFIG_KEXEC for crashkernel
parameter and vmcoreinfo related code as it can be reused without kexec
support.  Also, crashkernel parameter is reused instead of
fadump_reserve_mem to reserve memory for fadump.

The first patch moves crashkernel parameter parsing and vmcoreinfo
related code under CONFIG_CRASH_CORE instead of CONFIG_KEXEC_CORE.  The
second patch reuses the definitions of append_elf_note() & final_note()
functions under CONFIG_CRASH_CORE in IA64 arch code.  The third patch
removes dependency on CONFIG_KEXEC for firmware-assisted dump (fadump)
in powerpc.  The next patch reuses crashkernel parameter for reserving
memory for fadump, instead of the fadump_reserve_mem parameter.  This
has the advantage of using all syntaxes crashkernel parameter supports,
for fadump as well.  The last patch updates fadump kernel documentation
about use of crashkernel parameter.

This patch (of 5):

Traditionally, kdump is used to save vmcore in case of a crash.  Some
architectures like powerpc can save vmcore using architecture specific
support instead of kexec/kdump mechanism.  Such architecture specific
support also needs to reserve memory, to be used by dump capture kernel.
crashkernel parameter can be a reused, for memory reservation, by such
architecture specific infrastructure.

But currently, code related to vmcoreinfo and parsing of crashkernel
parameter is built under CONFIG_KEXEC_CORE.  This patch introduces
CONFIG_CRASH_CORE and moves the above mentioned code under this config,
allowing code reuse without dependency on CONFIG_KEXEC.  There is no
functional change with this patch.

Link: http://lkml.kernel.org/r/149035338104.6881.4550894432615189948.stgit@hbathini.in.ibm.comSigned-off-by: NHari Bathini <hbathini@linux.vnet.ibm.com>
Acked-by: NDave Young <dyoung@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

All the console driver handling code lives in printk.c.
Move console_init() there as well so console support can still be used
when the TTY code is configured out. No logical changes from this patch.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

If a console was specified by ACPI SPCR table _and_ command line
parameters like "console=ttyAMA0" _and_ "earlycon" were specified,
then log messages appear twice.

The root cause is that the code traverses the list of specified
consoles (the `console_cmdline` array) and stops at the first match.
But it may happen that the same console is referred by the elements
of this array twice:

	pl011,mmio,0x87e024000000,115200 -- from SPCR
	ttyAMA0 -- from command line

but in this case `preferred_console` points to the second entry and
the flag CON_CONSDEV is not set, so bootconsole is not deregistered.

To fix that, introduce an invariant "The last non-braille console
is always the preferred one" on the entries of the console_cmdline
array.  Then traverse it in reverse order to be sure that if
the console is preferred then it will be the first matching entry.
Introduce variable console_cmdline_cnt that keeps the number
of elements of the console_cmdline array (Petr Mladek).  It helps
to get rid of the loop that searches for the end of this array.

Link: http://lkml.kernel.org/r/20170405202006.18234-1-aleksey.makarov@linaro.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NAleksey Makarov <aleksey.makarov@linaro.org>
Reported-by: NSudeep Holla <sudeep.holla@arm.com>
Acked-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

The variable selected_console is set in __add_preferred_console()
to point to the last console parameter that was added to the
console_cmdline array.

Rename it to preferred_console so that the name reflects the usage.

Petr Mladek:
"[..] the selected_console/preferred_console
value is used to keep the console first in the console_drivers list.
IMHO, the main effect is that each line will first appear on this
console, see call_console_drivers(). But the message will still
appear also on all other enabled consoles. From this point,
the name "preferred" sounds better to me. More consoles
are selected (enabled) and only one is preferred (first)."

Link: http://lkml.kernel.org/r/20170315102854.1763-3-aleksey.makarov@linaro.org
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NAleksey Makarov <aleksey.makarov@linaro.org>
Suggested-by: NPeter Hurley <peter@hurleysoftware.com>
Acked-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

The variable preferred_console is used only inside register_console()
and its semantics is boolean.  It is negative when no console has been
made preferred.

Make it static bool and rename to has_preferred.

Renaming was suggested by Peter Hurley

Link: http://lkml.kernel.org/r/20170315102854.1763-2-aleksey.makarov@linaro.org
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NAleksey Makarov <aleksey.makarov@linaro.org>
Reviewed-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

Some console drivers code calls console_conditional_schedule()
that looks at @console_may_schedule. The value must be cleared
when the drivers are called from console_unlock() with
interrupts disabled. But rescheduling is fine when the same
code is called, for example, from tty operations where the
console semaphore is taken via console_lock().

This is why @console_may_schedule is cleared before calling console
drivers. The original value is stored to decide if we could sleep
between lines.

Now, @console_may_schedule is not cleared when we call
console_trylock() and jump back to the "again" goto label.
This has become a problem, since the commit 6b97a20d
("printk: set may_schedule for some of console_trylock() callers").
@console_may_schedule might get enabled now.

There is also the opposite problem. console_lock() can be called
only from preemptive context. It can always enable scheduling in
the console code. But console_trylock() is not able to detect it
when CONFIG_PREEMPT_COUNT is disabled. Therefore we should use the
original @console_may_schedule value after re-acquiring
the console semaphore in console_unlock().

This patch solves both problems by moving the "again" goto label.

Alternative solution was to clear and restore the value around
call_console_drivers(). Then console_conditional_schedule() could
be used also inside console_unlock(). But there was a potential race
with console_flush_on_panic() as reported by Sergey Senozhatsky.
That function should be called only where there is only one CPU
and with interrupts disabled. But better be on the safe side
because stopping CPUs might fail.

Fixes: 6b97a20d ("printk: set may_schedule for some of console_trylock() callers")
Link: http://lkml.kernel.org/r/1490372045-22288-1-git-send-email-pmladek@suse.comSuggested-by: NTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: linux-fbdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

There is no need to always call blocking console_lock() in
console_cpu_notify(), it's quite possible that console_sem can
be locked by other CPU on the system, either already printing
or soon to begin printing the messages. console_lock() in this
case can simply block CPU hotplug for unknown period of time
(console_unlock() is time unbound). Not that hotplug is very
fast, but still, with other CPUs being online and doing
printk() console_cpu_notify() can stuck.

Use console_trylock() instead and opt-out if console_sem is
already acquired from another CPU, since that CPU will do
the printing for us.

Link: http://lkml.kernel.org/r/20170121104729.8585-1-sergey.senozhatsky@gmail.com
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

We are going to split <linux/sched/task_stack.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/task_stack.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

We are going to split <linux/sched/debug.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/debug.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

We are going to split <linux/sched/clock.h> out of <linux/sched.h>, which
will have to be picked up from other headers and .c files.

Create a trivial placeholder <linux/sched/clock.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.
Acked-by: NLinus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Use rcuidle console tracepoint because, apparently, it may be issued
from an idle CPU:

  hw-breakpoint: Failed to enable monitor mode on CPU 0.
  hw-breakpoint: CPU 0 failed to disable vector catch

  ===============================
  [ ERR: suspicious RCU usage.  ]
  4.10.0-rc8-next-20170215+ #119 Not tainted
  -------------------------------
  ./include/trace/events/printk.h:32 suspicious rcu_dereference_check() usage!

  other info that might help us debug this:

  RCU used illegally from idle CPU!
  rcu_scheduler_active = 2, debug_locks = 0
  RCU used illegally from extended quiescent state!
  2 locks held by swapper/0/0:
   #0:  (cpu_pm_notifier_lock){......}, at: [<c0237e2c>] cpu_pm_exit+0x10/0x54
   #1:  (console_lock){+.+.+.}, at: [<c01ab350>] vprintk_emit+0x264/0x474

  stack backtrace:
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.10.0-rc8-next-20170215+ #119
  Hardware name: Generic OMAP4 (Flattened Device Tree)
    console_unlock
    vprintk_emit
    vprintk_default
    printk
    reset_ctrl_regs
    dbg_cpu_pm_notify
    notifier_call_chain
    cpu_pm_exit
    omap_enter_idle_coupled
    cpuidle_enter_state
    cpuidle_enter_state_coupled
    do_idle
    cpu_startup_entry
    start_kernel

This RCU warning, however, is suppressed by lockdep_off() in printk().
lockdep_off() increments the ->lockdep_recursion counter and thus
disables RCU_LOCKDEP_WARN() and debug_lockdep_rcu_enabled(), which want
lockdep to be enabled "current->lockdep_recursion == 0".

Link: http://lkml.kernel.org/r/20170217015932.11898-1-sergey.senozhatsky@gmail.comSigned-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reported-by: NTony Lindgren <tony@atomide.com>
Tested-by: NTony Lindgren <tony@atomide.com>
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Russell King <rmk@armlinux.org.uk>
Cc: <stable@vger.kernel.org> [3.4+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We do suppress_message_printing() check before we call
call_console_drivers() now, so `level' param is not needed
anymore.

Link: http://lkml.kernel.org/r/20161224140902.1962-2-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

This patch converts the rest of logbuf users (which are
out of printk recursion case, but can deadlock in printk).
To make printk-safe usage easier the patch introduces 4
helper macros:
- logbuf_lock_irq()/logbuf_unlock_irq()
  lock/unlock the logbuf lock and disable/enable local IRQ

- logbuf_lock_irqsave(flags)/logbuf_unlock_irqrestore(flags)
  lock/unlock the logbuf lock and saves/restores local IRQ state

Link: http://lkml.kernel.org/r/20161227141611.940-9-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Calvin Owens <calvinowens@fb.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

We use printk-safe now which makes printk-recursion detection code
in vprintk_emit() unreachable. The tricky thing here is that, apart
from detecting and reporting printk recursions, that code also used
to zap_locks() in case of panic() from the same CPU. However,
zap_locks() does not look to be needed anymore:

1) Since commit 08d78658 ("panic: release stale console lock to
   always get the logbuf printed out") panic flushing of `logbuf' to
   console ignores the state of `console_sem' by doing
   	panic()
		console_trylock();
		console_unlock();

2) Since commit cf9b1106 ("printk/nmi: flush NMI messages on the
   system panic") panic attempts to zap the `logbuf_lock' spin_lock to
   successfully flush nmi messages to `logbuf'.

Basically, it seems that we either already do what zap_locks() used to
do but in other places or we ignore the state of the lock. The only
reaming difference is that we don't re-init the console semaphore in
printk_safe_flush_on_panic(), but this is not necessary because we
don't call console drivers from printk_safe_flush_on_panic() due to
the fact that we are using a deferred printk() version (as was
suggested by Petr Mladek).

Link: http://lkml.kernel.org/r/20161227141611.940-8-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Calvin Owens <calvinowens@fb.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

Use printk_safe per-CPU buffers in printk recursion-prone blocks:
-- around logbuf_lock protected sections in vprintk_emit() and
   console_unlock()
-- around down_trylock_console_sem() and up_console_sem()

Note that this solution addresses deadlocks caused by printk()
recursive calls only. That is vprintk_emit() and console_unlock().
The rest will be converted in a followup patch.

Another thing to note is that we now keep lockdep enabled in printk,
because we are protected against the printk recursion caused by
lockdep in vprintk_emit() by the printk-safe mechanism - we first
switch to per-CPU buffers and only then access the deadlock-prone
locks.

Examples:

1) printk() from logbuf_lock spin_lock section

Assume the following code:
  printk()
    raw_spin_lock(&logbuf_lock);
    WARN_ON(1);
    raw_spin_unlock(&logbuf_lock);

which now produces:

 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 366 at kernel/printk/printk.c:1811 vprintk_emit
 CPU: 0 PID: 366 Comm: bash
 Call Trace:
   warn_slowpath_null+0x1d/0x1f
   vprintk_emit+0x1cd/0x438
   vprintk_default+0x1d/0x1f
   printk+0x48/0x50
  [..]

2) printk() from semaphore sem->lock spin_lock section

Assume the following code

  printk()
    console_trylock()
      down_trylock()
        raw_spin_lock_irqsave(&sem->lock, flags);
        WARN_ON(1);
        raw_spin_unlock_irqrestore(&sem->lock, flags);

which now produces:

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 363 at kernel/locking/semaphore.c:141 down_trylock
 CPU: 1 PID: 363 Comm: bash
 Call Trace:
   warn_slowpath_null+0x1d/0x1f
   down_trylock+0x3d/0x62
   ? vprintk_emit+0x3f9/0x414
   console_trylock+0x31/0xeb
   vprintk_emit+0x3f9/0x414
   vprintk_default+0x1d/0x1f
   printk+0x48/0x50
  [..]

3) printk() from console_unlock()

Assume the following code:

  printk()
    console_unlock()
      raw_spin_lock(&logbuf_lock);
      WARN_ON(1);
      raw_spin_unlock(&logbuf_lock);

which now produces:

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 329 at kernel/printk/printk.c:2384 console_unlock
 CPU: 1 PID: 329 Comm: bash
 Call Trace:
   warn_slowpath_null+0x18/0x1a
   console_unlock+0x12d/0x559
   ? trace_hardirqs_on_caller+0x16d/0x189
   ? trace_hardirqs_on+0xd/0xf
   vprintk_emit+0x363/0x374
   vprintk_default+0x18/0x1a
   printk+0x43/0x4b
  [..]

4) printk() from try_to_wake_up()

Assume the following code:

  printk()
    console_unlock()
      up()
        try_to_wake_up()
          raw_spin_lock_irqsave(&p->pi_lock, flags);
          WARN_ON(1);
          raw_spin_unlock_irqrestore(&p->pi_lock, flags);

which now produces:

 ------------[ cut here ]------------
 WARNING: CPU: 3 PID: 363 at kernel/sched/core.c:2028 try_to_wake_up
 CPU: 3 PID: 363 Comm: bash
 Call Trace:
   warn_slowpath_null+0x1d/0x1f
   try_to_wake_up+0x7f/0x4f7
   wake_up_process+0x15/0x17
   __up.isra.0+0x56/0x63
   up+0x32/0x42
   __up_console_sem+0x37/0x55
   console_unlock+0x21e/0x4c2
   vprintk_emit+0x41c/0x462
   vprintk_default+0x1d/0x1f
   printk+0x48/0x50
  [..]

5) printk() from call_console_drivers()

Assume the following code:
  printk()
    console_unlock()
      call_console_drivers()
      ...
          WARN_ON(1);

which now produces:

 ------------[ cut here ]------------
 WARNING: CPU: 2 PID: 305 at kernel/printk/printk.c:1604 call_console_drivers
 CPU: 2 PID: 305 Comm: bash
 Call Trace:
   warn_slowpath_null+0x18/0x1a
   call_console_drivers.isra.6.constprop.16+0x3a/0xb0
   console_unlock+0x471/0x48e
   vprintk_emit+0x1f4/0x206
   vprintk_default+0x18/0x1a
   vprintk_func+0x6e/0x70
   printk+0x3e/0x46
  [..]

6) unsupported placeholder in printk() format now prints an actual
   warning from vscnprintf(), instead of
   	'BUG: recent printk recursion!'.

 ------------[ cut here ]------------
 WARNING: CPU: 5 PID: 337 at lib/vsprintf.c:1900 format_decode
 Please remove unsupported %
  in format string
 CPU: 5 PID: 337 Comm: bash
 Call Trace:
   dump_stack+0x4f/0x65
   __warn+0xc2/0xdd
   warn_slowpath_fmt+0x4b/0x53
   format_decode+0x22c/0x308
   vsnprintf+0x89/0x3b7
   vscnprintf+0xd/0x26
   vprintk_emit+0xb4/0x238
   vprintk_default+0x1d/0x1f
   vprintk_func+0x6c/0x73
   printk+0x43/0x4b
  [..]

Link: http://lkml.kernel.org/r/20161227141611.940-7-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Calvin Owens <calvinowens@fb.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>

Account lost messages in pritk-safe and printk-safe-nmi
contexts and report those numbers during printk_safe_flush().

The patch also moves lost message counter to struct
`printk_safe_seq_buf' instead of having dedicated static
counters - this simplifies the code.

Link: http://lkml.kernel.org/r/20161227141611.940-6-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Calvin Owens <calvinowens@fb.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

This patch extends the idea of NMI per-cpu buffers to regions
that may cause recursive printk() calls and possible deadlocks.
Namely, printk() can't handle printk calls from schedule code
or printk() calls from lock debugging code (spin_dump() for instance);
because those may be called with `sem->lock' already taken or any
other `critical' locks (p->pi_lock, etc.). An example of deadlock
can be

 vprintk_emit()
  console_unlock()
   up()                        << raw_spin_lock_irqsave(&sem->lock, flags);
    wake_up_process()
     try_to_wake_up()
      ttwu_queue()
       ttwu_activate()
        activate_task()
         enqueue_task()
          enqueue_task_fair()
           cfs_rq_of()
            task_of()
             WARN_ON_ONCE(!entity_is_task(se))
              vprintk_emit()
               console_trylock()
                down_trylock()
                 raw_spin_lock_irqsave(&sem->lock, flags)
                 ^^^^ deadlock

and some other cases.

Just like in NMI implementation, the solution uses a per-cpu
`printk_func' pointer to 'redirect' printk() calls to a 'safe'
callback, that store messages in a per-cpu buffer and flushes
them back to logbuf buffer later.

Usage example:

 printk()
  printk_safe_enter_irqsave(flags)
  //
  //  any printk() call from here will endup in vprintk_safe(),
  //  that stores messages in a special per-CPU buffer.
  //
  printk_safe_exit_irqrestore(flags)

The 'redirection' mechanism, though, has been reworked, as suggested
by Petr Mladek. Instead of using a per-cpu @print_func callback we now
keep a per-cpu printk-context variable and call either default or nmi
vprintk function depending on its value. printk_nmi_entrer/exit and
printk_safe_enter/exit, thus, just set/celar corresponding bits in
printk-context functions.

The patch only adds printk_safe support, we don't use it yet.

Link: http://lkml.kernel.org/r/20161227141611.940-4-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Calvin Owens <calvinowens@fb.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>

vprintk(), just like printk(), better be using per-cpu printk_func
instead of direct vprintk_emit() call. Just in case if vprintk()
will ever be called from NMI, or from any other context that can
deadlock in printk().

Link: http://lkml.kernel.org/r/20161227141611.940-2-sergey.senozhatsky@gmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Calvin Owens <calvinowens@fb.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: NSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: NPetr Mladek <pmladek@suse.com>

This was entirely automated, using the script by Al:

  PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*<asm/uaccess.h>'
  sed -i -e "s!$PATT!#include <linux/uaccess.h>!" \
        $(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)

to do the replacement at the end of the merge window.
Requested-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If CONFIG_PRINTK=n:

    kernel/printk/printk.c:1893: warning: ‘cont’ defined but not used

Note that there are actually two different struct cont definitions and
objects: the first one is used if CONFIG_PRINTK=y, the second one became
unused by removing console_cont_flush().

Fixes: 5c2992ee ("printk: remove console flushing special cases for partial buffered lines")
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Acked-by: NPetr Mladek <pmladek@suse.com>
[ I do the occasional "allnoconfig" builds, but apparently not often
  enough  - Linus ]
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

It actively hurts proper merging, and makes for a lot of special cases.
There was a good(ish) reason for doing it originally, but it's getting
too painful to maintain.  And most of the original reasons for it are
long gone.

So instead of having special code to flush partial lines to the console
(as opposed to the record buffers), do _all_ the console writing from
the record buffer, and be done with it.

If an oops happens (or some other synchronous event), we will flush the
partial lines due to the oops printing activity, so this does not affect
that.  It does mean that if you have a completely hung machine, a
partial preceding line may not have been printed out.

That was some of the original reason for this complexity, in fact, back
when we used to test for the historical i386 "halt" instruction problem
by doing

	pr_info("Checking 'hlt' instruction... ");

	if (!boot_cpu_data.hlt_works_ok) {
		pr_cont("disabled\n");
		return;
	}
	halt();
	halt();
	halt();
	halt();
	pr_cont("OK\n");

and that model no longer works (it the 'hlt' instruction kills the
machine, the partial line won't have been flushed, so you won't even see
it).

Of course, that was also back in the days when people actually had
textual console output rather than a graphical splash-screen at bootup.
How times change..

Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Joe Perches <joe@perches.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Tested-by: NPetr Mladek <pmladek@suse.com>
Tested-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Tested-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The record logging code looks at the previous record flags in various
ways, and they are all wrong.

You can't use the previous record flags to determine anything about the
next record, because they may simply not be related.  In particular, the
reason the previous record was a continuation record may well be exactly
_because_ the new record was printed by a different process, which is
why the previous record was flushed.

So all those games are simply wrong, and make the code hard to
understand (because the code fundamentally cdoes not make sense).

So remove it.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kdb_trap_printk allows to pass normal printk() messages to kdb via
vkdb_printk().  For example, it is used to get backtrace using the
classic show_stack(), see kdb_show_stack().

vkdb_printf() tries to avoid a potential infinite loop by disabling the
trap.  But this approach is racy, for example:

CPU1					CPU2

vkdb_printf()
  // assume that kdb_trap_printk == 0
  saved_trap_printk = kdb_trap_printk;
  kdb_trap_printk = 0;

					kdb_show_stack()
					  kdb_trap_printk++;

Problem1: Now, a nested printk() on CPU0 calls vkdb_printf()
	  even when it should have been disabled. It will not
	  cause a deadlock but...

   // using the outdated saved value: 0
   kdb_trap_printk = saved_trap_printk;

					  kdb_trap_printk--;

Problem2: Now, kdb_trap_printk == -1 and will stay like this.
   It means that all messages will get passed to kdb from
   now on.

This patch removes the racy saved_trap_printk handling.  Instead, the
recursion is prevented by a check for the locked CPU.

The solution is still kind of racy.  A non-related printk(), from
another process, might get trapped by vkdb_printf().  And the wanted
printk() might not get trapped because kdb_printf_cpu is assigned.  But
this problem existed even with the original code.

A proper solution would be to get_cpu() before setting kdb_trap_printk
and trap messages only from this CPU.  I am not sure if it is worth the
effort, though.

In fact, the race is very theoretical.  When kdb is running any of the
commands that use kdb_trap_printk there is a single active CPU and the
other CPUs should be in a holding pen inside kgdb_cpu_enter().

The only time this is violated is when there is a timeout waiting for
the other CPUs to report to the holding pen.

Finally, note that the situation is a bit schizophrenic.  vkdb_printf()
explicitly allows recursion but only from KDB code that calls
kdb_printf() directly.  On the other hand, the generic printk()
recursion is not allowed because it might cause an infinite loop.  This
is why we could not hide the decision inside vkdb_printf() easily.

Link: http://lkml.kernel.org/r/1480412276-16690-4-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

copy_from_iter_full(), copy_from_iter_full_nocache() and
csum_and_copy_from_iter_full() - counterparts of copy_from_iter()
et.al., advancing iterator only in case of successful full copy
and returning whether it had been successful or not.

Convert some obvious users.  *NOTE* - do not blindly assume that
something is a good candidate for those unless you are sure that
not advancing iov_iter in failure case is the right thing in
this case.  Anything that does short read/short write kind of
stuff (or is in a loop, etc.) is unlikely to be a good one.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

The recent conversion of the console hotplug notifier to the state machine
missed the fact, that the notifier only operated on the non frozen
transitions. As a consequence the console_lock/unlock() pair is also
invoked during suspend, which results in a lockdep warning.

Restore the previous state by making the lock/unlock conditional on
!tasks_frozen.

Fixes: 90b14889 ("kernel/printk: Convert to hotplug state machine")
Reported-and-tested-by: NBorislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1611171729320.3645@nanosSigned-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

This reverts commit bfd8d3f2.

It turns out that this flushes things much too aggressiverly, and causes
lines to break up when the system logger races with new continuation
lines being printed.

There's a pending patch to make printk() flushing much more
straightforward, but it's too invasive for 4.9, so in the meantime let's
just not make the system message logging flush continuation lines.
They'll be flushed by the final newline anyway.
Suggested-by: NPetr Mladek <pmladek@suse.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This reverts commit 05fd007e ("console: don't prefer first
registered if DT specifies stdout-path").

The reverted commit changes existing behavior on which many ARM boards
rely.  Many ARM small-board-computers, like e.g.  the Raspberry Pi have
both a video output and a serial console.  Depending on whether the user
is using the device as a more regular computer; or as a headless device
we need to have the console on either one or the other.

Many users rely on the kernel behavior of the console being present on
both outputs, before the reverted commit the console setup with no
console= kernel arguments on an ARM board which sets stdout-path in dt
would look like this:

  [root@localhost ~]# cat /proc/consoles
  ttyS0                -W- (EC p a)    4:64
  tty0                 -WU (E  p  )    4:1

Where as after the reverted commit, it looks like this:

  [root@localhost ~]# cat /proc/consoles
  ttyS0                -W- (EC p a)    4:64

This commit reverts commit 05fd007e ("console: don't prefer first
registered if DT specifies stdout-path") restoring the original
behavior.

Fixes: 05fd007e ("console: don't prefer first registered if DT specifies stdout-path")
Link: http://lkml.kernel.org/r/20161104121135.4780-2-hdegoede@redhat.comSigned-off-by: NHans de Goede <hdegoede@redhat.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Cc: Thorsten Leemhuis <regressions@leemhuis.info>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Install the callbacks via the state machine.
Signed-off-by: NSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20161103145021.28528-3-bigeasy@linutronix.deSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

We have a fairly common pattern where you print several things as
continuations on one single line in a loop, and then at the end you do

	printk(KERN_CONT "\n");

to flush the buffered output.

But if the output was flushed by something else (concurrent printk
activity, or just system logging), we don't want that final flushing to
just print an empty line.

So just suppress empty continuation lines when they couldn't be merged
into the line they are a continuation of.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

That will mean that any possible subsequent continuation will now be
broken up onto a line of its own (since reading the log has finalized
the beginning og the line), but if user space has activated system
logging (or if there's a kernel message dump going on) that is the right
thing to do.

And now that we actually get the continuation flags _right_ for this
all, the user space logger that is reading the kernel messages can
actually see the continuation marker.  Not that anybody seems to really
bother with it (or care), but in theory user space can do its own
message stitching.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Avoid some duplicate logic now that we can return early, and update the
comments for the new LOG_CONT world order.

This also stops the continuation flushing from just using random record
flags for the flushing action, instead taking the flags from the proper
original line and updating them as we add continuations to it.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The code that actually decides how to log the message (whether to put it
directly into the record log, whether to append it to an existing
buffered log, or whether to start a new buffered log) is fairly
non-obvious code in the middle of the vprintk_emit() function.

Splitting that code up into a helper function makes it easier to
understand, but perhaps more importantly also allows for the code to
just return early out of the helper function once it has made the
decision about where the new log content goes.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Long long ago the kernel log buffer was a buffered stream of bytes, very
much like stdio in user space.  It supported log levels by scanning the
stream and noticing the log level markers at the beginning of each line,
but if you wanted to print a partial line in multiple chunks, you just
did multiple printk() calls, and it just automatically worked.

Except when it didn't, and you had very confusing output when different
lines got all mixed up with each other.  Then you got fragment lines
mixing with each other, or with non-fragment lines, because it was
traditionally impossible to tell whether a printk() call was a
continuation or not.

To at least help clarify the issue of continuation lines, we added a
KERN_CONT marker back in 2007 to mark continuation lines:

  47492527 ("printk: add KERN_CONT annotation").

That continuation marker was initially an empty string, and didn't
actuall make any semantic difference.  But it at least made it possible
to annotate the source code, and have check-patch notice that a printk()
didn't need or want a log level marker, because it was a continuation of
a previous line.

To avoid the ambiguity between a continuation line that had that
KERN_CONT marker, and a printk with no level information at all, we then
in 2009 made KERN_CONT be a real log level marker which meant that we
could now reliably tell the difference between the two cases.

  5fd29d6c ("printk: clean up handling of log-levels and newlines")

and we could take advantage of that to make sure we didn't mix up
continuation lines with lines that just didn't have any loglevel at all.

Then, in 2012, the kernel log buffer was changed to be a "record" based
log, where each line was a record that has a loglevel and a timestamp.

You can see the beginning of that conversion in commits

  e11fea92 ("kmsg: export printk records to the /dev/kmsg interface")
  7ff9554b ("printk: convert byte-buffer to variable-length record buffer")

with a number of follow-up commits to fix some painful fallout from that
conversion.  Over all, it took a couple of months to sort out most of
it.  But the upside was that you could have concurrent readers (and
writers) of the kernel log and not have lines with mixed output in them.

And one particular pain-point for the record-based kernel logging was
exactly the fragmentary lines that are generated in smaller chunks.  In
order to still log them as one recrod, the continuation lines need to be
attached to the previous record properly.

However the explicit continuation record marker that is actually useful
for this exact case was actually removed in aroundm the same time by commit

  61e99ab8 ("printk: remove the now unnecessary "C" annotation for KERN_CONT")

due to the incorrect belief that KERN_CONT wasn't meaningful.  The
ambiguity between "is this a continuation line" or "is this a plain
printk with no log level information" was reintroduced, and in fact
became an even bigger pain point because there was now the whole
record-level merging of kernel messages going on.

This patch reinstates the KERN_CONT as a real non-empty string marker,
so that the ambiguity is fixed once again.

But it's not a plain revert of that original removal: in the four years
since we made KERN_CONT an empty string again, not only has the format
of the log level markers changed, we've also had some usage changes in
this area.

For example, some ACPI code seems to use KERN_CONT _together_ with a log
level, and now uses both the KERN_CONT marker and (for example) a
KERN_INFO marker to show that it's an informational continuation of a
line.

Which is actually not a bad idea - if the continuation line cannot be
attached to its predecessor, without the log level information we don't
know what log level to assign to it (and we traditionally just assigned
it the default loglevel).  So having both a log level and the KERN_CONT
marker is not necessarily a bad idea, but it does mean that we need to
actually iterate over potentially multiple markers, rather than just a
single one.

Also, since KERN_CONT was still conceptually needed, and encouraged, but
didn't actually _do_ anything, we've also had the reverse problem:
rather than having too many annotations it has too few, and there is bit
rot with code that no longer marks the continuation lines with the
KERN_CONT marker.

So this patch not only re-instates the non-empty KERN_CONT marker, it
also fixes up the cases of bit-rot I noticed in my own logs.

There are probably other cases where KERN_CONT will be needed to be
added, either because it is new code that never dealt with the need for
KERN_CONT, or old code that has bitrotted without anybody noticing.

That said, we should strive to avoid the need for KERN_CONT.  It does
result in real problems for logging, and should generally not be seen as
a good feature.  If we some day can get rid of the feature entirely,
because nobody does any fragmented printk calls, that would be lovely.

But until that point, let's at mark the code that relies on the hacky
multi-fragment kernel printk's.  Not only does it avoid the ambiguity,
it also annotates code as "maybe this would be good to fix some day".

(That said, particularly during single-threaded bootup, the downsides of
KERN_CONT are very limited.  Things get much hairier when you have
multiple threads going on and user level reading and writing logs too).
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If a device tree specifies a preferred device for kernel console output
via the stdout-path or linux,stdout-path chosen node properties or the
stdout alias then the kernel ought to honor it & output the kernel
console to that device.  As it stands, this isn't the case.  Whilst we
parse the stdout-path properties & set an of_stdout variable from
of_alias_scan(), and use that from of_console_check() to determine
whether to add a console device as a preferred console whilst
registering it, we also prefer the first registered console if no other
has been selected at the time of its registration.

This means that if a console other than the one the device tree selects
via stdout-path is registered first, we will switch to using it & when
the stdout-path console is later registered the call to
add_preferred_console() via of_console_check() is too late to do
anything useful.  In practice this seems to mean that we switch to the
dummy console device fairly early & see no further console output:

    Console: colour dummy device 80x25
    console [tty0] enabled
    bootconsole [ns16550a0] disabled

Fix this by not automatically preferring the first registered console if
one is specified by the device tree.  This allows consoles to be
registered but not enabled, and once the driver for the console selected
by stdout-path calls of_console_check() the driver will be added to the
list of preferred consoles before any other console has been enabled.
When that console is then registered via register_console() it will be
enabled as expected.

Link: http://lkml.kernel.org/r/20160809151937.26118-1-paul.burton@imgtec.comSigned-off-by: NPaul Burton <paul.burton@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ivan Delalande <colona@arista.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Jan Kara <jack@suse.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Joe Perches <joe@perches.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This reverts commit 874f9c7d.

Geert Uytterhoeven reports:
 "This change seems to have an (unintendent?) side-effect.

  Before, pr_*() calls without a trailing newline characters would be
  printed with a newline character appended, both on the console and in
  the output of the dmesg command.

  After this commit, no new line character is appended, and the output
  of the next pr_*() call of the same type may be appended, like in:

    - Truncating RAM at 0x0000000040000000-0x00000000c0000000 to -0x0000000070000000
    - Ignoring RAM at 0x0000000200000000-0x0000000240000000 (!CONFIG_HIGHMEM)
    + Truncating RAM at 0x0000000040000000-0x00000000c0000000 to -0x0000000070000000Ignoring RAM at 0x0000000200000000-0x0000000240000000 (!CONFIG_HIGHMEM)"

Joe Perches says:
 "No, that is not intentional.

  The newline handling code inside vprintk_emit is a bit involved and
  for now I suggest a revert until this has all the same behavior as
  earlier"
Reported-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Requested-by: NJoe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In commit 874f9c7d ("printk: create pr_<level> functions"), new
pr_level defines were added to printk.c.

These new defines are guarded by an #ifdef CONFIG_PRINTK - however,
there is already a surrounding #ifdef CONFIG_PRINTK starting a lot
earlier in line 249 which means the newly introduced #ifdef is
unnecessary.

Let's remove it to avoid confusion.
Signed-off-by: NAndreas Ziegler <andreas.ziegler@fau.de>
Cc: Joe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Add a "printk.devkmsg" kernel command line parameter which controls how
userspace writes into /dev/kmsg.  It has three options:

 * ratelimit - ratelimit logging from userspace.
 * on  - unlimited logging from userspace
 * off - logging from userspace gets ignored

The default setting is to ratelimit the messages written to it.

This changes the kernel default setting of "on" to "ratelimit" and we do
that because we want to keep userspace spamming /dev/kmsg to sane
levels.  This is especially moot when a small kernel log buffer wraps
around and messages get lost.  So the ratelimiting setting should be a
sane setting where kernel messages should have a bit higher chance of
survival from all the spamming.

It additionally does not limit logging to /dev/kmsg while the system is
booting if we haven't disabled it on the command line.

Furthermore, we can control the logging from a lower priority sysctl
interface - kernel.printk_devkmsg.

That interface will succeed only if printk.devkmsg *hasn't* been
supplied on the command line.  If it has, then printk.devkmsg is a
one-time setting which remains for the duration of the system lifetime.
This "locking" of the setting is to prevent userspace from changing the
logging on us through sysctl(2).

This patch is based on previous patches from Linus and Steven.

[bp@suse.de: fixes]
  Link: http://lkml.kernel.org/r/20160719072344.GC25563@nazgul.tnic
Link: http://lkml.kernel.org/r/20160716061745.15795-3-bp@alien8.deSigned-off-by: NBorislav Petkov <bp@suse.de>
Cc: Dave Young <dyoung@redhat.com>
Cc: Franck Bui <fbui@suse.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

asm-generic headers are generic implementations for architecture
specific code and should not be included by common code.  Thus use the
asm/ version of sections.h to get at the linker sections.

Link: http://lkml.kernel.org/r/1468285008-7331-1-git-send-email-hch@lst.deSigned-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Messages' levels and console log level are inspected when the actual
printing occurs, which may provoke console_unlock() and
console_cont_flush() to waste CPU cycles on every message that has
loglevel above the current console_loglevel.

Schematically, console_unlock() does the following:

console_unlock()
{
        ...
        for (;;) {
                ...
                raw_spin_lock_irqsave(&logbuf_lock, flags);
skip:
                msg = log_from_idx(console_idx);

                if (msg->flags & LOG_NOCONS) {
                        ...
                        goto skip;
                }

                level = msg->level;
                len += msg_print_text();                        >> sprintfs
                                                                   memcpy,
                                                                   etc.

                if (nr_ext_console_drivers) {
                        ext_len = msg_print_ext_header();       >> scnprintf
                        ext_len += msg_print_ext_body();        >> scnprintfs
                                                                   etc.
                }
                ...
                raw_spin_unlock(&logbuf_lock);

                call_console_drivers(level, ext_text, ext_len, text, len)
                {
                        if (level >= console_loglevel &&        >> drop the message
                                        !ignore_loglevel)
                                return;

                        console->write(...);
                }

                local_irq_restore(flags);
        }
        ...
}

The thing here is this deferred `level >= console_loglevel' check.  We
are wasting CPU cycles on sprintfs/memcpy/etc.  preparing the messages
that we will eventually drop.

This can be huge when we register a new CON_PRINTBUFFER console, for
instance.  For every such a console register_console() resets the

        console_seq, console_idx, console_prev

and sets a `exclusive console' pointer to replay the log buffer to that
just-registered console.  And there can be a lot of messages to replay,
in the worst case most of which can be dropped after console_loglevel
test.

We know messages' levels long before we call msg_print_text() and
friends, so we can just move console_loglevel check out of
call_console_drivers() and format a new message only if we are sure that
it won't be dropped.

The patch factors out loglevel check into suppress_message_printing()
function and tests message->level and console_loglevel before formatting
functions in console_unlock() and console_cont_flush() are getting
executed.  This improves things not only for exclusive CON_PRINTBUFFER
consoles, but for every console_unlock() that attempts to print a
message of level above the console_loglevel.

Link: http://lkml.kernel.org/r/20160627135012.8229-1-sergey.senozhatsky@gmail.comSigned-off-by: NSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Calvin Owens <calvinowens@fb.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Using functions instead of macros can reduce overall code size by
eliminating unnecessary "KERN_SOH<digit>" prefixes from format strings.

  defconfig x86-64:

  $ size vmlinux*
     text    data     bss      dec     hex  filename
  10193570 4331464 1105920 15630954  ee826a vmlinux.new
  10192623 4335560 1105920 15634103  ee8eb7 vmlinux.old

As the return value are unimportant and unused in the kernel tree, these
new functions return void.

Miscellanea:

 - change pr_<level> macros to call new __pr_<level> functions
 - change vprintk_nmi and vprintk_default to add LOGLEVEL_<level> argument

[akpm@linux-foundation.org: fix LOGLEVEL_INFO, per Joe]
Link: http://lkml.kernel.org/r/e16cc34479dfefcae37c98b481e6646f0f69efc3.1466718827.git.joe@perches.comSigned-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>