The current implementation of RCU_FAST_NO_HZ tries reasonably hard to rid
the current CPU of RCU callbacks.  This is appropriate when the CPU is
entering idle, where it doesn't have much useful to do anyway, but is most
definitely not what you want when transitioning to user-mode execution.
This commit therefore detects the adaptive-tick case, and refrains from
burning CPU time getting rid of RCU callbacks in that case.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In some cases, it is necessary to enter or exit userspace-RCU-idle mode
from an interrupt handler, for example, if some other CPU sends this
CPU a resched IPI.  In this case, the current CPU would enter the IPI
handler in userspace-RCU-idle mode, but would need to exit the IPI handler
after having exited that mode.

To allow this to work, this commit adds two new APIs to TREE_RCU:

- rcu_user_enter_after_irq(). This must be called from an interrupt between
rcu_irq_enter() and rcu_irq_exit().  After the irq calls rcu_irq_exit(),
the irq handler will return into an RCU extended quiescent state.
In theory, this interrupt is never a nested interrupt, but in practice
it might interrupt softirq, which looks to RCU like a nested interrupt.

- rcu_user_exit_after_irq(). This must be called from a non-nesting
interrupt, interrupting an RCU extended quiescent state, also
between rcu_irq_enter() and rcu_irq_exit(). After the irq calls
rcu_irq_exit(), the irq handler will return in an RCU non-quiescent
state.

[ Combined with "Allow calls to rcu_exit_user_irq from nesting irqs." ]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

RCU currently insists that only idle tasks can enter RCU idle mode, which
prohibits an adaptive tickless kernel (AKA nohz cpusets), which in turn
would mean that usermode execution would always take scheduling-clock
interrupts, even when there is only one task runnable on the CPU in
question.

This commit therefore adds rcu_user_enter() and rcu_user_exit(), which
allow non-idle tasks to enter RCU idle mode.  These are quite similar
to rcu_idle_enter() and rcu_idle_exit(), respectively, except that they
omit the idle-task checks.

[ Updated to use "user" flag rather than separate check functions. ]

[ paulmck: Updated to drop exports of new functions based on Josh's patch
  getting rid of the need for them. ]
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

Resolved conflict in kernel/sched/core.c using Peter Zijlstra's
approach from https://lkml.org/lkml/2012/9/5/585.

The conflicts between kernel/rcutree.h and kernel/rcutree_plugin.h
were due to adjacent insertions and deletions, which were resolved
by simply accepting the changes on both branches.

Merge Linux 3.6-rc7, to pick up fixes and to resolve a conflict in an
upcoming pull.
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Merge branches 'bigrt.2012.09.23a', 'doctorture.2012.09.23a', 'fixes.2012.09.23a', 'hotplug.2012.09.23a' and 'idlechop.2012.09.23a' into HEAD

bigrt.2012.09.23a contains additional commits to reduce scheduling latency
	from RCU on huge systems (many hundrends or thousands of CPUs).

doctorture.2012.09.23a contains documentation changes and rcutorture fixes.

fixes.2012.09.23a contains miscellaneous fixes.

hotplug.2012.09.23a contains CPU-hotplug-related changes.

idle.2012.09.23a fixes architectures for which RCU no longer considered
	the idle loop to be a quiescent state due to earlier
	adaptive-dynticks changes.  Affected architectures are alpha,
	cris, frv, h8300, m32r, m68k, mn10300, parisc, score, xtensa,
	and ia64.

Pull kbuild fixes from Michal Marek:
 "There are two more kbuild fixes for 3.6.

  One fixes a race between x86's archscripts target and the rule
  (re)building scripts/basic/fixdep.  The second is a fix for the
  previous attempt at fixing make firmware_install with make 3.82.
  This new solution should work with any version of GNU make"

* 'rc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild:
  x86/kbuild: archscripts depends on scripts_basic
  firmware: fix directory creation rule matching with make 3.80

Pull hwmon subsystem fixes from Jean Delvare.

* 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jdelvare/staging:
  hwmon: (fam15h_power) Tweak runavg_range on resume
  hwmon: (coretemp) Use get_online_cpus to avoid races involving CPU hotplug
  hwmon: (via-cputemp) Use get_online_cpus to avoid races involving CPU hotplug

Pull SCSI fixes from James Bottomley:
 "This is a set of four essential fixes: two oops related (bnx2i,
  virtio-scsi), one data corruption related (hpsa) and one failure to
  boot due to interrupt routing issues (mpt2ss).

  Signed-off-by: James Bottomley <JBottomley@Parallels.com>"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  [SCSI] hpsa: fix handling of protocol error
  [SCSI] mpt2sas: Fix for issue - Unable to boot from the drive connected to HBA
  [SCSI] bnx2i: Fixed NULL ptr deference for 1G bnx2 Linux iSCSI offload
  [SCSI] scsi: virtio-scsi: Fix address translation failure of HighMem pages used by sg list

Fix potential NULL pointer dereference in edac_unregister_sysfs() on
system boot introduced in 3.6-rc1.

Since commit 7a623c03 ("edac: rewrite the sysfs code to use struct
device") edac_mc_alloc() no longer initializes embedded kobjects in
struct mem_ctl_info.  Therefore edac_mc_free() can no longer simply
decrement a kobject reference count to free the allocated memory unless
the memory controller driver module had also called edac_mc_add_mc().

Now edac_mc_free() will check if the newly embedded struct device has
been registered with sysfs before using either the standard device
release functions or freeing the data structures itself with logic
pulled out of the error path of edac_mc_alloc().

The BUG this patch resolves for me:

  BUG: unable to handle kernel NULL pointer dereference at   (null)
  EIP is at __wake_up_common+0x1a/0x6a
  Process modprobe (pid: 933, ti=f3dc6000 task=f3db9520 task.ti=f3dc6000)
  Call Trace:
    complete_all+0x3f/0x50
    device_pm_remove+0x23/0xa2
    device_del+0x34/0x142
    edac_unregister_sysfs+0x3b/0x5c [edac_core]
    edac_mc_free+0x29/0x2f [edac_core]
    e7xxx_probe1+0x268/0x311 [e7xxx_edac]
    e7xxx_init_one+0x56/0x61 [e7xxx_edac]
    local_pci_probe+0x13/0x15
  ...

Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: NShaun Ruffell <sruffell@digium.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

coccinelle warns about:

+ drivers/edac/edac_mc.c:429:9-23: ERROR: reference preceded by free on line 429

   421         if (mci->csrows) {
 > 422                 for (chn = 0; chn < tot_channels; chn++) {
   423                         csr = mci->csrows[chn];
   424                         if (csr) {
 > 425                                 for (chn = 0; chn < tot_channels; chn++)
   426                                          kfree(csr->channels[chn]);
   427                                  kfree(csr);
   428                          }
 > 429                          kfree(mci->csrows[i]);
   430                  }
   431                  kfree(mci->csrows);
   432          }

and that code block seem to mess things up in several ways (double free, memory
leak, out-of-bound reads etc.):

L422: The iterator "chn" and bound "tot_channels" are totally wrong. Should be
      "row" and "tot_csrows" respectively. Which means either memory leak, or
      out-of-bound reads (which if does not trigger an immediate page fault
      error, will further lead to kfree() on random addresses).

L425: The inner loop is reusing the same iterator "chn" as the outer loop,
      which could lead to premature end of the outer loop, and hence memory leak.

L429: The array index 'i' in mci->csrows[i] is a temporary value used in
      previous loops, and won't change at all in the current loop. Which
      means either out-of-bound read and possibly kfree(random number), or the
      same mci->csrows[i] get freed once and again, and possibly double free
      for the kfree(csr) in L427.

L426/L427: a kfree(csr->channels) is needed in between to avoid leaking the memory.

The buggy code was introduced by commit de3910eb ("edac: change the mem
allocation scheme to make Documentation/kobject.txt happy") in the 3.6-rc1
merge window. Fix it by freeing up resources in this order:

  free csrows[i]->channels[j]
  free csrows[i]->channels
  free csrows[i]
  free csrows

CC: Mauro Carvalho Chehab <mchehab@redhat.com>
CC: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The quirk introduced with commit
00250ec9 (hwmon: fam15h_power: fix
bogus values with current BIOSes) is not only required during driver
load but also when system resumes from suspend. The BIOS might set the
previously recommended (but unsuitable) initilization value for the
running average range register during resume.
Signed-off-by: NAndreas Herrmann <andreas.herrmann3@amd.com>
Tested-by: NAndreas Hartmann <andihartmann@01019freenet.de>
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Cc: stable@vger.kernel.org # 3.0+

coretemp_init loops with for_each_online_cpu, adding platform_devices
and sysfs interfaces, then calls register_hotcpu_notifier.  There is a
race if a CPU is offlined or onlined after the loop, but before
register_hotcpu_notifier.  The race might result in the absence of a
platform_device+sysfs interface for an online CPU, or the presence of
a platform_device+sysfs interface for an offline CPU.  A similar race
occurs during coretemp_exit, after the module calls
unregister_hotcpu_notifier, but before it unregisters all devices, a
CPU might offline and a device for an offline CPU will exist for a
short while.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier
with get_online_cpus+put_online_cpus; and surrounds
unregister_hotcpu_notifier and device unregistering with
get_online_cpus+put_online_cpus.

Build tested.
Signed-off-by: NSilas Boyd-Wickizer <sbw@mit.edu>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

via_cputemp_init loops with for_each_online_cpu, adding
platform_devices, then calls register_hotcpu_notifier.  If a CPU is
offlined between the loop and register_hotcpu_notifier, then later
onlined, via_cputemp_device_add will attempt to add platform devices
with the same ID.  A similar race occurs during via_cputemp_exit,
after the module calls unregister_hotcpu_notifier, a CPU might offline
and a device will exist for a CPU that is offline.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier
with get_online_cpus+put_online_cpus; and surrounds
unregister_hotcpu_notifier and device unregistering with
get_online_cpus+put_online_cpus.

Build tested.
Signed-off-by: NSilas Boyd-Wickizer <sbw@mit.edu>
Acked-by: NHarald Welte <laforge@gnumonks.org>
Signed-off-by: NJean Delvare <khali@linux-fr.org>

Traditionally, the entire idle task served as an RCU quiescent state.
But when RCU read side critical sections started appearing within the
idle loop, this traditional strategy became untenable.  The fix was to
create new RCU APIs named rcu_idle_enter() and rcu_idle_exit(), which
must be called by each architecture's idle loop so that RCU can tell
when it is safe to ignore a given idle CPU.

Unfortunately, this fix was never applied to ia64, a shortcoming remedied
by this commit.

Reported by: Tony Luck <tony.luck@intel.com>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested by: Tony Luck <tony.luck@intel.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the xtensa's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in scores's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Chen Liqin <liqin.chen@sunplusct.com>
Cc: Lennox Wu <lennox.wu@gmail.com>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the parisc's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Parisc <linux-parisc@vger.kernel.org>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the mn10300's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the m68k's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Acked-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Cc: m68k <linux-m68k@lists.linux-m68k.org>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the m32r's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the h8300's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the Frv's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: <stable@vger.kernel.org> # 3.3+
Acked-by: NDavid Howells <dhowells@redhat.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the Cris's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Cris <linux-cris-kernel@axis.com>
Cc: <stable@vger.kernel.org> # 3.3+
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

In the old times, the whole idle task was considered
as an RCU quiescent state. But as RCU became more and
more successful overtime, some RCU read side critical
section have been added even in the code of some
architectures idle tasks, for tracing for example.

So nowadays, rcu_idle_enter() and rcu_idle_exit() must
be called by the architecture to tell RCU about the part
in the idle loop that doesn't make use of rcu read side
critical sections, typically the part that puts the CPU
in low power mode.

This is necessary for RCU to find the quiescent states in
idle in order to complete grace periods.

Add this missing pair of calls in the Alpha's idle loop.
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Tested-by: NMichael Cree <mcree@orcon.net.nz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: alpha <linux-alpha@vger.kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: <stable@vger.kernel.org> # 3.3+
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

cpu_idle() is called on the boot CPU by the init code with
preemption disabled. But the cpu_idle() function in alpha
doesn't handle this when it calls schedule() directly.

Fix it by converting it into schedule_preempt_disabled().

Also disable preemption before calling cpu_idle() from
secondary CPU entry code to stay consistent with this
state.
Signed-off-by: NFrederic Weisbecker <fweisbec@gmail.com>
Tested-by: NMichael Cree <mcree@orcon.net.nz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: alpha <linux-alpha@vger.kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

If arch/x86/kernel/cpuid.c is a module, a CPU might offline or online
between the for_each_online_cpu() loop and the call to
register_hotcpu_notifier in cpuid_init or the call to
unregister_hotcpu_notifier in cpuid_exit.  The potential races can
lead to leaks/duplicates, attempts to destroy non-existant devices, or
random pointer dereferences.

For example, in cpuid_exit if:

        for_each_online_cpu(cpu)
                cpuid_device_destroy(cpu);
        class_destroy(cpuid_class);
        __unregister_chrdev(CPUID_MAJOR, 0, NR_CPUS, "cpu/cpuid");
        <----- CPU onlines
        unregister_hotcpu_notifier(&cpuid_class_cpu_notifier);

the hotcpu notifier will attempt to create a device for the
cpuid_class, which the module already destroyed.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier or
unregister_hotcpu_notifier with get_online_cpus+put_online_cpus.

Tested on a VM.
Signed-off-by: NSilas Boyd-Wickizer <sbw@mit.edu>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

If arch/x86/kernel/msr.c is a module, a CPU might offline or online
between the for_each_online_cpu(i) loop and the call to
register_hotcpu_notifier in msr_init or the call to
unregister_hotcpu_notifier in msr_exit. The potential races can lead
to leaks/duplicates, attempts to destroy non-existant devices, or
random pointer dereferences.

For example, in msr_init if:

        for_each_online_cpu(i) {
                err = msr_device_create(i);
                if (err != 0)
                        goto out_class;
        }
        <----- CPU offlines
        register_hotcpu_notifier(&msr_class_cpu_notifier);

and the CPU never onlines before msr_exit, then the module will never
call msr_device_destroy for the associated CPU.

This fix surrounds for_each_online_cpu and register_hotcpu_notifier or
unregister_hotcpu_notifier with get_online_cpus+put_online_cpus.

Tested on a VM.
Signed-off-by: NSilas Boyd-Wickizer <sbw@mit.edu>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Rabik and Paul reported two different issues related to the same few
lines of code.

Rabik's issue is that the nr_uninterruptible migration code is wrong in
that he sees artifacts due to this (Rabik please do expand in more
detail).

Paul's issue is that this code as it stands relies on us using
stop_machine() for unplug, we all would like to remove this assumption
so that eventually we can remove this stop_machine() usage altogether.

The only reason we'd have to migrate nr_uninterruptible is so that we
could use for_each_online_cpu() loops in favour of
for_each_possible_cpu() loops, however since nr_uninterruptible() is the
only such loop and its using possible lets not bother at all.

The problem Rabik sees is (probably) caused by the fact that by
migrating nr_uninterruptible we screw rq->calc_load_active for both rqs
involved.

So don't bother with fancy migration schemes (meaning we now have to
keep using for_each_possible_cpu()) and instead fold any nr_active delta
after we migrate all tasks away to make sure we don't have any skewed
nr_active accounting.

[ paulmck: Move call to calc_load_migration to CPU_DEAD to avoid
miscounting noted by Rakib. ]
Reported-by: NRakib Mullick <rakib.mullick@gmail.com>
Reported-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>

Posting a callback after the CPU_DEAD notifier effectively leaks
that callback unless/until that CPU comes back online.  Silence is
unhelpful when attempting to track down such leaks, so this commit emits
a WARN_ON_ONCE() and unconditionally leaks the callback when an offline
CPU attempts to register a callback.  The rdp->nxttail[RCU_NEXT_TAIL] is
set to NULL in the CPU_DEAD notifier and restored in the CPU_UP_PREPARE
notifier, allowing _call_rcu() to determine exactly when posting callbacks
is illegal.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

Currently, _rcu_barrier() relies on preempt_disable() to prevent
any CPU from going offline, which in turn depends on CPU hotplug's
use of __stop_machine().

This patch therefore makes _rcu_barrier() use get_online_cpus() to
block CPU-hotplug operations.  This has the added benefit of removing
the need for _rcu_barrier() to adopt callbacks:  Because CPU-hotplug
operations are excluded, there can be no callbacks to adopt.  This
commit simplifies the code accordingly.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

The print_cpu_stall_fast_no_hz() function attempts to print -1 when
the ->idle_gp_timer is not pending, but unsigned arithmetic causes it
to instead print ULONG_MAX, which is 4294967295 on 32-bit systems and
18446744073709551615 on 64-bit systems.  Neither of these are the most
reader-friendly values, so this commit instead causes "timer not pending"
to be printed when ->idle_gp_timer is not pending.
Reported-by: NPaul Walmsley <paul@pwsan.com>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

TINY_RCU's rcu_idle_enter_common() invokes rcu_sched_qs() in order
to inform the RCU core of the quiescent state implied by idle entry.
Of course, idle is also an extended quiescent state, so that the call
to rcu_sched_qs() speeds up RCU's invoking of any callbacks that might
be queued.  This speed-up is important when entering into dyntick-idle
mode -- if there are no further scheduling-clock interrupts, the callbacks
might never be invoked, which could result in a system hang.

However, processing callbacks does event tracing, which in turn
implies RCU read-side critical sections, which are illegal in extended
quiescent states.  This patch therefore moves the call to rcu_sched_qs()
so that it precedes the point at which we inform lockdep that RCU has
entered an extended quiescent state.
Signed-off-by: NLi Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>

This patch replaces list_for_each_continue_rcu() with
list_for_each_entry_continue_rcu() to save a few lines
of code and allow removing list_for_each_continue_rcu().
Signed-off-by: NMichael Wang <wangyun@linux.vnet.ibm.com>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

The can_stop_idle_tick() function complains if a softirq vector is
raised too late in the idle-entry process, presumably in order to
prevent dangling softirq invocations from being delayed across the
full idle period, which might be indefinitely long -- and if softirq
was asserted any later than the call to this function, such a delay
might well happen.

However, RCU needs to be able to use softirq to stop idle entry in
order to be able to drain RCU callbacks from the current CPU, which in
turn enables faster entry into dyntick-idle mode, which in turn reduces
power consumption.  Because RCU takes this action at a well-defined
point in the idle-entry path, it is safe for RCU to take this approach.

This commit therefore silences the error message that is sometimes
produced when the going-idle CPU suddenly finds that it has an RCU_SOFTIRQ
to process.  The error message will continue to be issued for other
softirq vectors.
Reported-by: NSedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: NSedat Dilek <sedat.dilek@gmail.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

The use of raw_local_irq_save() is unnecessary, given that local_irq_save()
really does disable interrupts.  Also, it appears to interfere with lockdep.
Therefore, this commit moves to local_irq_save().
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: NFengguang Wu <fengguang.wu@intel.com>

The first memory barrier in __call_rcu() is supposed to order any
updates done beforehand by the caller against the actual queuing
of the callback.  However, the second memory barrier (which is intended
to order incrementing the queue lengths before queuing the callback)
is also between the caller's updates and the queuing of the callback.
The second memory barrier can therefore serve both purposes.

This commit therefore removes the first memory barrier.
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

If a given CPU avoids the idle loop but also avoids starting a new
RCU grace period for a full minute, RCU can issue spurious RCU CPU
stall warnings.  This commit fixes this issue by adding a check for
ongoing grace period to avoid these spurious stall warnings.
Reported-by: NBecky Bruce <bgillbruce@gmail.com>
Signed-off-by: NPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>