The clocksource delta to nanoseconds conversion is using signed math, but
the delta is unsigned. This makes the conversion space smaller than
necessary and in case of a multiplication overflow the conversion can
become negative. The conversion is done with scaled math:

    s64 nsec_delta = ((s64)clkdelta * clk->mult) >> clk->shift;

Shifting a signed integer right obvioulsy preserves the sign, which has
interesting consequences:
 
 - Time jumps backwards
 
 - __iter_div_u64_rem() which is used in one of the calling code pathes
   will take forever to piecewise calculate the seconds/nanoseconds part.

This has been reported by several people with different scenarios:

David observed that when stopping a VM with a debugger:

 "It was essentially the stopped by debugger case.  I forget exactly why,
  but the guest was being explicitly stopped from outside, it wasn't just
  scheduling lag.  I think it was something in the vicinity of 10 minutes
  stopped."

 When lifting the stop the machine went dead.

The stopped by debugger case is not really interesting, but nevertheless it
would be a good thing not to die completely.

But this was also observed on a live system by Liav:

 "When the OS is too overloaded, delta will get a high enough value for the
  msb of the sum delta * tkr->mult + tkr->xtime_nsec to be set, and so
  after the shift the nsec variable will gain a value similar to
  0xffffffffff000000."

Unfortunately this has been reintroduced recently with commit 6bd58f09
("time: Add cycles to nanoseconds translation"). It had been fixed a year
ago already in commit 35a4933a ("time: Avoid signed overflow in
timekeeping_get_ns()").

Though it's not surprising that the issue has been reintroduced because the
function itself and the whole call chain uses s64 for the result and the
propagation of it. The change in this recent commit is subtle:

   s64 nsec;

-  nsec = (d * m + n) >> s:
+  nsec = d * m + n;
+  nsec >>= s;

d being type of cycle_t adds another level of obfuscation.

This wouldn't have happened if the previous change to unsigned computation
would have made the 'nsec' variable u64 right away and a follow up patch
had cleaned up the whole call chain.

There have been patches submitted which basically did a revert of the above
patch leaving everything else unchanged as signed. Back to square one. This
spawned a admittedly pointless discussion about potential users which rely
on the unsigned behaviour until someone pointed out that it had been fixed
before. The changelogs of said patches added further confusion as they made
finally false claims about the consequences for eventual users which expect
signed results.

Despite delta being cycle_t, aka. u64, it's very well possible to hand in
a signed negative value and the signed computation will happily return the
correct result. But nobody actually sat down and analyzed the code which
was added as user after the propably unintended signed conversion.

Though in sensitive code like this it's better to analyze it proper and
make sure that nothing relies on this than hunting the subtle wreckage half
a year later. After analyzing all call chains it stands that no caller can
hand in a negative value (which actually would work due to the s64 cast)
and rely on the signed math to do the right thing.

Change the conversion function to unsigned math. The conversion of all call
chains is done in a follow up patch.

This solves the starvation issue, which was caused by the negative result,
but it does not solve the underlying problem. It merily procrastinates
it. When the timekeeper update is deferred long enough that the unsigned
multiplication overflows, then time going backwards is observable again.

It does neither solve the issue of clocksources with a small counter width
which will wrap around possibly several times and cause random time stamps
to be generated. But those are usually not found on systems used for
virtualization, so this is likely a non issue.

I took the liberty to claim authorship for this simply because
analyzing all callsites and writing the changelog took substantially
more time than just making the simple s/s64/u64/ change and ignore the
rest.

Fixes: 6bd58f09 ("time: Add cycles to nanoseconds translation")
Reported-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reported-by: NLiav Rehana <liavr@mellanox.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Acked-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Parit Bhargava <prarit@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>
Cc: "Christopher S. Hall" <christopher.s.hall@intel.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20161208204228.688545601@linutronix.deSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Alarm timers are one of the mechanisms to wake up a system from suspend,
but there exist no tracepoints to analyse which process/thread armed an
alarmtimer.

Add tracepoints for start/cancel/expire of individual alarm timers and one
for tracing the suspend time decision when to resume the system.

The following trace excerpt illustrates the new mechanism:

Binder:3292_2-3304  [000] d..2   149.981123: alarmtimer_cancel:
alarmtimer:ffffffc1319a7800 type:REALTIME
expires:1325463120000000000 now:1325376810370370245

Binder:3292_2-3304  [000] d..2   149.981136: alarmtimer_start:
alarmtimer:ffffffc1319a7800 type:REALTIME
expires:1325376840000000000 now:1325376810370384591

Binder:3292_9-3953  [000] d..2   150.212991: alarmtimer_cancel:
alarmtimer:ffffffc1319a5a00 type:BOOTTIME
expires:179552000000 now:150154008122

Binder:3292_9-3953  [000] d..2   150.213006: alarmtimer_start:
alarmtimer:ffffffc1319a5a00 type:BOOTTIME
expires:179551000000 now:150154025622

system_server-3000  [002] ...1  162.701940: alarmtimer_suspend:
alarmtimer type:REALTIME expires:1325376840000000000

The wakeup time which is selected at suspend time allows to map it back to
the task arming the timer: Binder:3292_2.

[ tglx: Store alarm timer expiry time instead of some useless RTC relative
  	information, add proper type information for wakeups which are
  	handled via the clock_nanosleep/freezer and massage the changelog. ]
Signed-off-by: NBaolin Wang <baolin.wang@linaro.org>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Link: http://lkml.kernel.org/r/1480372524-15181-5-git-send-email-john.stultz@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Unlike monotonic clock, boot clock as a trace clock will account for
time spent in suspend useful for tracing suspend/resume. This uses
earlier introduced infrastructure for using the fast boot clock.
Signed-off-by: NJoel Fernandes <joelaf@google.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Link: http://lkml.kernel.org/r/1480372524-15181-7-git-send-email-john.stultz@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

This boot clock can be used as a tracing clock and will account for
suspend time.

To keep it NMI safe since we're accessing from tracing, we're not using a
separate timekeeper with updates to monotonic clock and boot offset
protected with seqlocks. This has the following minor side effects:

(1) Its possible that a timestamp be taken after the boot offset is updated
but before the timekeeper is updated. If this happens, the new boot offset
is added to the old timekeeping making the clock appear to update slightly
earlier:
   CPU 0                                        CPU 1
   timekeeping_inject_sleeptime64()
   __timekeeping_inject_sleeptime(tk, delta);
                                                timestamp();
   timekeeping_update(tk, TK_CLEAR_NTP...);

(2) On 32-bit systems, the 64-bit boot offset (tk->offs_boot) may be
partially updated.  Since the tk->offs_boot update is a rare event, this
should be a rare occurrence which postprocessing should be able to handle.
Signed-off-by: NJoel Fernandes <joelaf@google.com>
Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1480372524-15181-6-git-send-email-john.stultz@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Some embedded systems have no use for them.  This removes about
25KB from the kernel binary size when configured out.

Corresponding syscalls are routed to a stub logging the attempt to
use those syscalls which should be enough of a clue if they were
disabled without proper consideration. They are: timer_create,
timer_gettime: timer_getoverrun, timer_settime, timer_delete,
clock_adjtime, setitimer, getitimer, alarm.

The clock_settime, clock_gettime, clock_getres and clock_nanosleep
syscalls are replaced by simple wrappers compatible with CLOCK_REALTIME,
CLOCK_MONOTONIC and CLOCK_BOOTTIME only which should cover the vast
majority of use cases with very little code.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Acked-by: NRichard Cochran <richardcochran@gmail.com>
Acked-by: NThomas Gleixner <tglx@linutronix.de>
Acked-by: NJohn Stultz <john.stultz@linaro.org>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kbuild@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Michal Marek <mmarek@suse.com>
Cc: Edward Cree <ecree@solarflare.com>
Link: http://lkml.kernel.org/r/1478841010-28605-7-git-send-email-nicolas.pitre@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

There is no logical relation between add_device_randomness() and
posix_cpu_timers_exit(). Let's move the former to where the later
is called. This way, when posix-cpu-timers.c is compiled out, there
is no need to worry about not losing a call to add_device_randomness().
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Acked-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kbuild@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Michal Marek <mmarek@suse.com>
Cc: Edward Cree <ecree@solarflare.com>
Link: http://lkml.kernel.org/r/1478841010-28605-6-git-send-email-nicolas.pitre@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Move the only user of alarm_setitimer to itimer.c where it is defined.
This allows for making alarm_setitimer static, and dropping it from the
build when __ARCH_WANT_SYS_ALARM is not defined.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Acked-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: linux-kbuild@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Michal Marek <mmarek@suse.com>
Cc: Edward Cree <ecree@solarflare.com>
Link: http://lkml.kernel.org/r/1478841010-28605-5-git-send-email-nicolas.pitre@linaro.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

The documentation for schedule_timeout(), schedule_hrtimeout(), and
schedule_hrtimeout_range() all claim that the routines couldn't possibly
return early if the task state was TASK_UNINTERRUPTIBLE. This is simply
not true since wake_up_process() will cause those routines to exit early.

We cannot make schedule_[hr]timeout() loop until the timeout expires if the
task state is uninterruptible because we have users which rely on the
existing and designed behaviour.

Make the documentation match the (correct) implementation.

schedule_hrtimeout() returns -EINTR even when a uninterruptible task was
woken up. This might look strange, but making the return code depend on the
state is too much of an effort as it would affect all the call sites. There
is no value in doing so, but we spell it out clearly in the documentation.
Suggested-by: NDaniel Kurtz <djkurtz@chromium.org>
Signed-off-by: NDouglas Anderson <dianders@chromium.org>
Cc: huangtao@rock-chips.com
Cc: heiko@sntech.de
Cc: broonie@kernel.org
Cc: briannorris@chromium.org
Cc: Andreas Mohr <andi@lisas.de>
Cc: linux-rockchip@lists.infradead.org
Cc: tony.xie@rock-chips.com
Cc: John Stultz <john.stultz@linaro.org>
Cc: linux@roeck-us.net
Cc: tskd08@gmail.com
Link: http://lkml.kernel.org/r/1477065531-30342-2-git-send-email-dianders@chromium.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Users of usleep_range() expect that it will _never_ return in less time
than the minimum passed parameter. However, nothing in the code ensures
this, when the sleeping task is woken by wake_up_process() or any other
mechanism which can wake a task from uninterruptible state.

Neither usleep_range() nor schedule_hrtimeout_range*() have any protection
against wakeups. schedule_hrtimeout_range*() is designed this way despite
the fact that the API documentation does not mention it.

msleep() already has code to handle this case since it will loop as long
as there was still time left.  usleep_range() has no such loop, add it.

Presumably this problem was not detected before because usleep_range() is
only used in a few places and the function is mostly used in contexts which
are not exposed to wakeups of any form.

An effort was made to look for users relying on the old behavior by
looking for usleep_range() in the same file as wake_up_process().
No problems were found by this search, though it is conceivable that
someone could have put the sleep and wakeup in two different files.

An effort was made to ask several upstream maintainers if they were aware
of people relying on wake_up_process() to wake up usleep_range(). No
maintainers were aware of that but they were aware of many people relying
on usleep_range() never returning before the minimum.
Reported-by: NTao Huang <huangtao@rock-chips.com>
Signed-off-by: NDouglas Anderson <dianders@chromium.org>
Cc: heiko@sntech.de
Cc: broonie@kernel.org
Cc: briannorris@chromium.org
Cc: Andreas Mohr <andi@lisas.de>
Cc: linux-rockchip@lists.infradead.org
Cc: tony.xie@rock-chips.com
Cc: John Stultz <john.stultz@linaro.org>
Cc: djkurtz@chromium.org
Cc: linux@roeck-us.net
Cc: tskd08@gmail.com
Link: http://lkml.kernel.org/r/1477065531-30342-1-git-send-email-dianders@chromium.orgSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

The TPS65217 driver grew interrupt support which uses
irq_set_parent(). While it's not yet clear why this is used in the first
place, building the driver as a module fails with:

 ERROR: ".irq_set_parent" [drivers/mfd/tps65217.ko] undefined!

The correctness of the driver change is still investigated, but for now
it's less trouble to export irq_set_parent() than dealing with the build
wreckage.

[ tglx: Rewrote changelog and made the export GPL ]

Fixes: 6556bdac ("mfd: tps65217: Add support for IRQs")
Signed-off-by: NSudip Mukherjee <sudip.mukherjee@codethink.co.uk>
Cc: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Marcin Niestroj <m.niestroj@grinn-global.com>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Lee Jones <lee.jones@linaro.org>
Link: http://lkml.kernel.org/r/1475775403-27207-1-git-send-email-sudipm.mukherjee@gmail.comSigned-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>

This removes the 'write' argument from access_process_vm() and replaces
it with 'gup_flags' as use of this function previously silently implied
FOLL_FORCE, whereas after this patch callers explicitly pass this flag.

We make this explicit as use of FOLL_FORCE can result in surprising
behaviour (and hence bugs) within the mm subsystem.
Signed-off-by: NLorenzo Stoakes <lstoakes@gmail.com>
Acked-by: NJesper Nilsson <jesper.nilsson@axis.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This removes the 'write' and 'force' from get_user_pages_remote() and
replaces them with 'gup_flags' to make the use of FOLL_FORCE explicit in
callers as use of this flag can result in surprising behaviour (and
hence bugs) within the mm subsystem.
Signed-off-by: NLorenzo Stoakes <lstoakes@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

A scheduler performance regression has been reported by Joseph Salisbury,
which he bisected back to:

  3d30544f ("sched/fair: Apply more PELT fixes)

The regression triggers when several levels of task groups are involved
(read: SystemD) and cpu_possible_mask != cpu_present_mask.

The root cause is that group entity's load (tg_child->se[i]->avg.load_avg)
is initialized to scale_load_down(se->load.weight). During the creation of
a child task group, its group entities on possible CPUs are attached to
parent's cfs_rq (tg_parent) and their loads are added to the parent's load
(tg_parent->load_avg) with update_tg_load_avg().

But only the load on online CPUs will then be updated to reflect real load,
whereas load on other CPUs will stay at the initial value.

The result is a tg_parent->load_avg that is higher than the real load, the
weight of group entities (tg_parent->se[i]->load.weight) on online CPUs is
smaller than it should be, and the task group gets a less running time than
what it could expect.

( This situation can be detected with /proc/sched_debug. The ".tg_load_avg"
  of the task group will be much higher than sum of ".tg_load_avg_contrib"
  of online cfs_rqs of the task group. )

The load of group entities don't have to be intialized to something else
than 0 because their load will increase when an entity is attached.
Reported-by: NJoseph Salisbury <joseph.salisbury@canonical.com>
Tested-by: NDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: NVincent Guittot <vincent.guittot@linaro.org>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: <stable@vger.kernel.org> # 4.8.x
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: joonwoop@codeaurora.org
Fixes: 3d30544f ("sched/fair: Apply more PELT fixes)
Link: http://lkml.kernel.org/r/1476881123-10159-1-git-send-email-vincent.guittot@linaro.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

Remove the set but unused variable base in alarm_clock_get to fix the
following warning when building with 'W=1':

  kernel/time/alarmtimer.c: In function ‘alarm_timer_create’:
  kernel/time/alarmtimer.c:545:21: warning: variable ‘base’ set but not used [-Wunused-but-set-variable]
Signed-off-by: NTobias Klauser <tklauser@distanz.ch>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20161017094702.10873-1-tklauser@distanz.chSigned-off-by: NThomas Gleixner <tglx@linutronix.de>

Use distinctive name for cpu_hotplug.dep_map to avoid the actual
cpu_hotplug.lock appearing as cpu_hotplug.lock#2 in lockdep splats.
Signed-off-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Acked-by: NGautham R. Shenoy <ego@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Gautham R . Shenoy <ego@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: intel-gfx@lists.freedesktop.org
Cc: trivial@kernel.org
Signed-off-by: NIngo Molnar <mingo@kernel.org>

This affectively reverts commit 377ccbb4 ("Makefile: Mute warning
for __builtin_return_address(>0) for tracing only") because it turns out
that it really isn't tracing only - it's all over the tree.

We already also had the warning disabled separately for mm/usercopy.c
(which this commit also removes), and it turns out that we will also
want to disable it for get_lock_parent_ip(), that is used for at least
TRACE_IRQFLAGS.  Which (when enabled) ends up being all over the tree.

Steven Rostedt had a patch that tried to limit it to just the config
options that actually triggered this, but quite frankly, the extra
complexity and abstraction just isn't worth it.  We have never actually
had a case where the warning is actually useful, so let's just disable
it globally and not worry about it.
Acked-by: NSteven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Previously hung_task_panic would not be respected if enabled after
hung_task_warnings had already been decremented to 0.

Permit the kernel to panic if hung_task_panic is enabled after
hung_task_warnings has already been decremented to 0 and another task
hangs for hung_task_timeout_secs seconds.

Check if hung_task_panic is enabled so we don't return prematurely, and
check if hung_task_warnings is non-zero so we don't print the warning
unnecessarily.

[akpm@linux-foundation.org: fix off-by-one]
Link: http://lkml.kernel.org/r/1473450214-4049-1-git-send-email-jsiddle@redhat.comSigned-off-by: NJohn Siddle <jsiddle@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch allows to make kthread worker freezable via a new @flags
parameter. It will allow to avoid an init work in some kthreads.

It currently does not affect the function of kthread_worker_fn()
but it might help to do some optimization or fixes eventually.

I currently do not know about any other use for the @flags
parameter but I believe that we will want more flags
in the future.

Finally, I hope that it will not cause confusion with @flags member
in struct kthread. Well, I guess that we will want to rework the
basic kthreads implementation once all kthreads are converted into
kthread workers or workqueues. It is possible that we will merge
the two structures.

Link: http://lkml.kernel.org/r/1470754545-17632-12-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There are situations when we need to modify the delay of a delayed kthread
work. For example, when the work depends on an event and the initial delay
means a timeout. Then we want to queue the work immediately when the event
happens.

This patch implements kthread_mod_delayed_work() as inspired workqueues.
It cancels the timer, removes the work from any worker list and queues it
again with the given timeout.

A very special case is when the work is being canceled at the same time.
It might happen because of the regular kthread_cancel_delayed_work_sync()
or by another kthread_mod_delayed_work(). In this case, we do nothing and
let the other operation win. This should not normally happen as the caller
is supposed to synchronize these operations a reasonable way.

Link: http://lkml.kernel.org/r/1470754545-17632-11-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We are going to use kthread workers more widely and sometimes we will need
to make sure that the work is neither pending nor running.

This patch implements cancel_*_sync() operations as inspired by
workqueues.  Well, we are synchronized against the other operations via
the worker lock, we use del_timer_sync() and a counter to count parallel
cancel operations.  Therefore the implementation might be easier.

First, we check if a worker is assigned.  If not, the work has newer been
queued after it was initialized.

Second, we take the worker lock.  It must be the right one.  The work must
not be assigned to another worker unless it is initialized in between.

Third, we try to cancel the timer when it exists.  The timer is deleted
synchronously to make sure that the timer call back is not running.  We
need to temporary release the worker->lock to avoid a possible deadlock
with the callback.  In the meantime, we set work->canceling counter to
avoid any queuing.

Fourth, we try to remove the work from a worker list. It might be
the list of either normal or delayed works.

Fifth, if the work is running, we call kthread_flush_work().  It might
take an arbitrary time.  We need to release the worker-lock again.  In the
meantime, we again block any queuing by the canceling counter.

As already mentioned, the check for a pending kthread work is done under a
lock.  In compare with workqueues, we do not need to fight for a single
PENDING bit to block other operations.  Therefore we do not suffer from
the thundering storm problem and all parallel canceling jobs might use
kthread_flush_work().  Any queuing is blocked until the counter gets zero.

Link: http://lkml.kernel.org/r/1470754545-17632-10-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We are going to use kthread_worker more widely and delayed works
will be pretty useful.

The implementation is inspired by workqueues.  It uses a timer to queue
the work after the requested delay.  If the delay is zero, the work is
queued immediately.

In compare with workqueues, each work is associated with a single worker
(kthread).  Therefore the implementation could be much easier.  In
particular, we use the worker->lock to synchronize all the operations with
the work.  We do not need any atomic operation with a flags variable.

In fact, we do not need any state variable at all.  Instead, we add a list
of delayed works into the worker.  Then the pending work is listed either
in the list of queued or delayed works.  And the existing check of pending
works is the same even for the delayed ones.

A work must not be assigned to another worker unless reinitialized.
Therefore the timer handler might expect that dwork->work->worker is valid
and it could simply take the lock.  We just add some sanity checks to help
with debugging a potential misuse.

Link: http://lkml.kernel.org/r/1470754545-17632-9-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Nothing currently prevents a work from queuing for a kthread worker when
it is already running on another one.  This means that the work might run
in parallel on more than one worker.  Also some operations are not
reliable, e.g.  flush.

This problem will be even more visible after we add kthread_cancel_work()
function.  It will only have "work" as the parameter and will use
worker->lock to synchronize with others.

Well, normally this is not a problem because the API users are sane.
But bugs might happen and users also might be crazy.

This patch adds a warning when we try to insert the work for another
worker.  It does not fully prevent the misuse because it would make the
code much more complicated without a big benefit.

It adds the same warning also into kthread_flush_work() instead of the
repeated attempts to get the right lock.

A side effect is that one needs to explicitly reinitialize the work if it
must be queued into another worker.  This is needed, for example, when the
worker is stopped and started again.  It is a bit inconvenient.  But it
looks like a good compromise between the stability and complexity.

I have double checked all existing users of the kthread worker API and
they all seems to initialize the work after the worker gets started.

Just for completeness, the patch adds a check that the work is not already
in a queue.

The patch also puts all the checks into a separate function.  It will be
reused when implementing delayed works.

Link: http://lkml.kernel.org/r/1470754545-17632-8-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The current kthread worker users call flush() and stop() explicitly.
This function does the same plus it frees the kthread_worker struct
in one call.

It is supposed to be used together with kthread_create_worker*() that
allocates struct kthread_worker.

Link: http://lkml.kernel.org/r/1470754545-17632-7-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Kthread workers are currently created using the classic kthread API,
namely kthread_run().  kthread_worker_fn() is passed as the @threadfn
parameter.

This patch defines kthread_create_worker() and
kthread_create_worker_on_cpu() functions that hide implementation details.

They enforce using kthread_worker_fn() for the main thread.  But I doubt
that there are any plans to create any alternative.  In fact, I think that
we do not want any alternative main thread because it would be hard to
support consistency with the rest of the kthread worker API.

The naming and function of kthread_create_worker() is inspired by the
workqueues API like the rest of the kthread worker API.

The kthread_create_worker_on_cpu() variant is motivated by the original
kthread_create_on_cpu().  Note that we need to bind per-CPU kthread
workers already when they are created.  It makes the life easier.
kthread_bind() could not be used later for an already running worker.

This patch does _not_ convert existing kthread workers.  The kthread
worker API need more improvements first, e.g.  a function to destroy the
worker.

IMPORTANT:

kthread_create_worker_on_cpu() allows to use any format of the worker
name, in compare with kthread_create_on_cpu().  The good thing is that it
is more generic.  The bad thing is that most users will need to pass the
cpu number in two parameters, e.g.  kthread_create_worker_on_cpu(cpu,
"helper/%d", cpu).

To be honest, the main motivation was to avoid the need for an empty
va_list.  The only legal way was to create a helper function that would be
called with an empty list.  Other attempts caused compilation warnings or
even errors on different architectures.

There were also other alternatives, for example, using #define or
splitting __kthread_create_worker().  The used solution looked like the
least ugly.

Link: http://lkml.kernel.org/r/1470754545-17632-6-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kthread_create_on_node() implements a bunch of logic to create the
kthread.  It is already called by kthread_create_on_cpu().

We are going to extend the kthread worker API and will need to call
kthread_create_on_node() with va_list args there.

This patch does only a refactoring and does not modify the existing
behavior.

Link: http://lkml.kernel.org/r/1470754545-17632-5-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kthread_create_on_cpu() was added by the commit 2a1d4460
("kthread: Implement park/unpark facility").  It is currently used only
when enabling new CPU.  For this purpose, the newly created kthread has to
be parked.

The CPU binding is a bit tricky.  The kthread is parked when the CPU has
not been allowed yet.  And the CPU is bound when the kthread is unparked.

The function would be useful for more per-CPU kthreads, e.g.
bnx2fc_thread, fcoethread.  For this purpose, the newly created kthread
should stay in the uninterruptible state.

This patch moves the parking into smpboot.  It binds the thread already
when created.  Then the function might be used universally.  Also the
behavior is consistent with kthread_create() and kthread_create_on_node().

Link: http://lkml.kernel.org/r/1470754545-17632-4-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

A good practice is to prefix the names of functions by the name
of the subsystem.

The kthread worker API is a mix of classic kthreads and workqueues.  Each
worker has a dedicated kthread.  It runs a generic function that process
queued works.  It is implemented as part of the kthread subsystem.

This patch renames the existing kthread worker API to use
the corresponding name from the workqueues API prefixed by
kthread_:

__init_kthread_worker()		-> __kthread_init_worker()
init_kthread_worker()		-> kthread_init_worker()
init_kthread_work()		-> kthread_init_work()
insert_kthread_work()		-> kthread_insert_work()
queue_kthread_work()		-> kthread_queue_work()
flush_kthread_work()		-> kthread_flush_work()
flush_kthread_worker()		-> kthread_flush_worker()

Note that the names of DEFINE_KTHREAD_WORK*() macros stay
as they are. It is common that the "DEFINE_" prefix has
precedence over the subsystem names.

Note that INIT() macros and init() functions use different
naming scheme. There is no good solution. There are several
reasons for this solution:

  + "init" in the function names stands for the verb "initialize"
    aka "initialize worker". While "INIT" in the macro names
    stands for the noun "INITIALIZER" aka "worker initializer".

  + INIT() macros are used only in DEFINE() macros

  + init() functions are used close to the other kthread()
    functions. It looks much better if all the functions
    use the same scheme.

  + There will be also kthread_destroy_worker() that will
    be used close to kthread_cancel_work(). It is related
    to the init() function. Again it looks better if all
    functions use the same naming scheme.

  + there are several precedents for such init() function
    names, e.g. amd_iommu_init_device(), free_area_init_node(),
    jump_label_init_type(),  regmap_init_mmio_clk(),

  + It is not an argument but it was inconsistent even before.

[arnd@arndb.de: fix linux-next merge conflict]
 Link: http://lkml.kernel.org/r/20160908135724.1311726-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/1470754545-17632-3-git-send-email-pmladek@suse.comSuggested-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "kthread: Kthread worker API improvements"

The intention of this patchset is to make it easier to manipulate and
maintain kthreads.  Especially, I want to replace all the custom main
cycles with a generic one.  Also I want to make the kthreads sleep in a
consistent state in a common place when there is no work.

This patch (of 11):

A good practice is to prefix the names of functions by the name of the
subsystem.

This patch fixes the name of probe_kthread_data().  The other wrong
functions names are part of the kthread worker API and will be fixed
separately.

Link: http://lkml.kernel.org/r/1470754545-17632-2-git-send-email-pmladek@suse.comSigned-off-by: NPetr Mladek <pmladek@suse.com>
Suggested-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

As of Android N, SECCOMP is required. Without it, we will get
mediaextractor error:

E /system/bin/mediaextractor: libminijail: prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER): Invalid argument

Link: http://lkml.kernel.org/r/20160908185934.18098-3-robh@kernel.orgSigned-off-by: NRob Herring <robh@kernel.org>
Acked-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Android won't boot without SELinux enabled, so make it the default.

Link: http://lkml.kernel.org/r/20160908185934.18098-2-robh@kernel.orgSigned-off-by: NRob Herring <robh@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

CONFIG_MD is in recommended, but other dependent options like DM_CRYPT and
DM_VERITY options are in base.  The result is the options in base don't
get enabled when applying both base and recommended fragments.  Move all
the options to recommended.

Link: http://lkml.kernel.org/r/20160908185934.18098-1-robh@kernel.orgSigned-off-by: NRob Herring <robh@kernel.org>
Acked-by: NJohn Stultz <john.stultz@linaro.org>
Cc: Amit Pundir <amit.pundir@linaro.org>
Cc: Dmitry Shmidt <dimitrysh@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Option is long gone, see commit 5d9efa7e ("ipv6: Remove privacy
config option.")

Link: http://lkml.kernel.org/r/20160811170340.9859-1-bp@alien8.deSigned-off-by: NBorislav Petkov <bp@suse.de>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Relay avoids calling wake_up_interruptible() for doing the wakeup of
readers/consumers, waiting for the generation of new data, from the
context of a process which produced the data.  This is apparently done to
prevent the possibility of a deadlock in case Scheduler itself is is
generating data for the relay, after acquiring rq->lock.

The following patch used a timer (to be scheduled at next jiffy), for
delegating the wakeup to another context.
	commit 7c9cb383
	Author: Tom Zanussi <zanussi@comcast.net>
	Date:   Wed May 9 02:34:01 2007 -0700

	relay: use plain timer instead of delayed work

	relay doesn't need to use schedule_delayed_work() for waking readers
	when a simple timer will do.

Scheduling a plain timer, at next jiffies boundary, to do the wakeup
causes a significant wakeup latency for the Userspace client, which makes
relay less suitable for the high-frequency low-payload use cases where the
data gets generated at a very high rate, like multiple sub buffers getting
filled within a milli second.  Moreover the timer is re-scheduled on every
newly produced sub buffer so the timer keeps getting pushed out if sub
buffers are filled in a very quick succession (less than a jiffy gap
between filling of 2 sub buffers).  As a result relay runs out of sub
buffers to store the new data.

By using irq_work it is ensured that wakeup of userspace client, blocked
in the poll call, is done at earliest (through self IPI or next timer
tick) enabling it to always consume the data in time.  Also this makes
relay consistent with printk & ring buffers (trace), as they too use
irq_work for deferred wake up of readers.

[arnd@arndb.de: select CONFIG_IRQ_WORK]
 Link: http://lkml.kernel.org/r/20160912154035.3222156-1-arnd@arndb.de
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/1472906487-1559-1-git-send-email-akash.goel@intel.comSigned-off-by: NPeter Zijlstra <peterz@infradead.org>
Signed-off-by: NAkash Goel <akash.goel@intel.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Daniel Walker reported problems which happens when
crash_kexec_post_notifiers kernel option is enabled
(https://lkml.org/lkml/2015/6/24/44).

In that case, smp_send_stop() is called before entering kdump routines
which assume other CPUs are still online.  As the result, for x86, kdump
routines fail to save other CPUs' registers and disable virtualization
extensions.

To fix this problem, call a new kdump friendly function,
crash_smp_send_stop(), instead of the smp_send_stop() when
crash_kexec_post_notifiers is enabled.  crash_smp_send_stop() is a weak
function, and it just call smp_send_stop().  Architecture codes should
override it so that kdump can work appropriately.  This patch only
provides x86-specific version.

For Xen's PV kernel, just keep the current behavior.

NOTES:

- Right solution would be to place crash_smp_send_stop() before
  __crash_kexec() invocation in all cases and remove smp_send_stop(), but
  we can't do that until all architectures implement own
  crash_smp_send_stop()

- crash_smp_send_stop()-like work is still needed by
  machine_crash_shutdown() because crash_kexec() can be called without
  entering panic()

Fixes: f06e5153 (kernel/panic.c: add "crash_kexec_post_notifiers" option)
Link: http://lkml.kernel.org/r/20160810080948.11028.15344.stgit@sysi4-13.yrl.intra.hitachi.co.jpSigned-off-by: NHidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Reported-by: NDaniel Walker <dwalker@fifo99.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Daniel Walker <dwalker@fifo99.com>
Cc: Xunlei Pang <xpang@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Toshi Kani <toshi.kani@hpe.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: David Daney <david.daney@cavium.com>
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: "Steven J. Hill" <steven.hill@cavium.com>
Cc: Corey Minyard <cminyard@mvista.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

On __ptrace_detach(), called from do_exit()->exit_notify()->
forget_original_parent()->exit_ptrace(), the TIF_SYSCALL_TRACE in
thread->flags of the tracee is not cleared up.  This results in the
tracehook_report_syscall_* being called (though there's no longer a tracer
listening to that) upon its further syscalls.

Example scenario - attach "strace" to a running process and kill it (the
strace) with SIGKILL.  You'll see that the syscall trace hooks are still
being called.

The clearing of this flag should be moved from ptrace_detach() to
__ptrace_detach().

Link: http://lkml.kernel.org/r/1472759493-20554-1-git-send-email-alnovak@suse.czSigned-off-by: NAles Novak <alnovak@suse.cz>
Acked-by: NOleg Nesterov <oleg@redhat.com>
Cc: Jiri Kosina <jkosina@suse.cz>
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/1473602302-6208-1-git-send-email-hch@lst.deSigned-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit:

  10e2f1ac ("sched/core: Rewrite and improve select_idle_siblings()")

... improved select_idle_sibling(), but also triggered a regression (crash)
during CPU-hotplug:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000078
  IP: [<ffffffffb10cd332>] select_idle_sibling+0x1c2/0x4f0
  Call Trace:
   <IRQ>
    select_task_rq_fair+0x749/0x930
    ? select_task_rq_fair+0xb4/0x930
    ? __lock_is_held+0x54/0x70
    try_to_wake_up+0x19a/0x5b0
    default_wake_function+0x12/0x20
    autoremove_wake_function+0x12/0x40
    __wake_up_common+0x55/0x90
    __wake_up+0x39/0x50
    wake_up_klogd_work_func+0x40/0x60
    irq_work_run_list+0x57/0x80
    irq_work_run+0x2c/0x30
    smp_irq_work_interrupt+0x2e/0x40
    irq_work_interrupt+0x96/0xa0
   <EOI>
    ? _raw_spin_unlock_irqrestore+0x45/0x80
    try_to_wake_up+0x4a/0x5b0
    wake_up_state+0x10/0x20
    __kthread_unpark+0x67/0x70
    kthread_unpark+0x22/0x30
    cpuhp_online_idle+0x3e/0x70
    cpu_startup_entry+0x6a/0x450
    start_secondary+0x154/0x180

This can be reproduced by running the ftrace test case of kselftest, the
test case will hot-unplug the CPU and the CPU will attach to the NULL
sched-domain during scheduler teardown.

The step 2 for the rewrite select_idle_siblings():

  | Step 2) tracks the average cost of the scan and compares this to the
  | average idle time guestimate for the CPU doing the wakeup.

If the CPU which doing the wakeup is the going hot-unplug CPU, then NULL
sched domain will be dereferenced to acquire the average cost of the scan.

This patch fix it by failing the search of an idle CPU in the LLC process
if this sched domain is NULL.
Tested-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWanpeng Li <wanpeng.li@hotmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1475971443-3187-1-git-send-email-wanpeng.li@hotmail.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

The __latent_entropy gcc attribute can be used only on functions and
variables.  If it is on a function then the plugin will instrument it for
gathering control-flow entropy. If the attribute is on a variable then
the plugin will initialize it with random contents.  The variable must
be an integer, an integer array type or a structure with integer fields.

These specific functions have been selected because they are init
functions (to help gather boot-time entropy), are called at unpredictable
times, or they have variable loops, each of which provide some level of
latent entropy.
Signed-off-by: NEmese Revfy <re.emese@gmail.com>
[kees: expanded commit message]
Signed-off-by: NKees Cook <keescook@chromium.org>

This adds a new gcc plugin named "latent_entropy". It is designed to
extract as much possible uncertainty from a running system at boot time as
possible, hoping to capitalize on any possible variation in CPU operation
(due to runtime data differences, hardware differences, SMP ordering,
thermal timing variation, cache behavior, etc).

At the very least, this plugin is a much more comprehensive example for
how to manipulate kernel code using the gcc plugin internals.

The need for very-early boot entropy tends to be very architecture or
system design specific, so this plugin is more suited for those sorts
of special cases. The existing kernel RNG already attempts to extract
entropy from reliable runtime variation, but this plugin takes the idea to
a logical extreme by permuting a global variable based on any variation
in code execution (e.g. a different value (and permutation function)
is used to permute the global based on loop count, case statement,
if/then/else branching, etc).

To do this, the plugin starts by inserting a local variable in every
marked function. The plugin then adds logic so that the value of this
variable is modified by randomly chosen operations (add, xor and rol) and
random values (gcc generates separate static values for each location at
compile time and also injects the stack pointer at runtime). The resulting
value depends on the control flow path (e.g., loops and branches taken).

Before the function returns, the plugin mixes this local variable into
the latent_entropy global variable. The value of this global variable
is added to the kernel entropy pool in do_one_initcall() and _do_fork(),
though it does not credit any bytes of entropy to the pool; the contents
of the global are just used to mix the pool.

Additionally, the plugin can pre-initialize arrays with build-time
random contents, so that two different kernel builds running on identical
hardware will not have the same starting values.
Signed-off-by: NEmese Revfy <re.emese@gmail.com>
[kees: expanded commit message and code comments]
Signed-off-by: NKees Cook <keescook@chromium.org>