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The local_clock/cpu_clock functions were changed to prevent a double
identical test with sched_clock_cpu() when HAVE_UNSTABLE_SCHED_CLOCK
is set. That resulted in one line functions.
As these functions are in all the cases one line functions and in the
hot path, it is useful to specify them as static inline in order to
give a strong hint to the compiler.
After verification, it appears the compiler does not inline them
without this hint. Change those functions to static inline.
sched_clock_cpu() is called via the inlined local_clock()/cpu_clock()
functions from sched.h. So any module code including sched.h will
reference sched_clock_cpu(). Thus it must be exported with the
EXPORT_SYMBOL_GPL macro.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1460385514-14700-2-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In case the HAVE_UNSTABLE_SCHED_CLOCK config is set, the cpu_clock() version
checks if sched_clock_stable() is not set and calls sched_clock_cpu(),
otherwise it calls sched_clock().
sched_clock_cpu() checks also if sched_clock_stable() is set and, if true,
calls sched_clock().
sched_clock() will be called in sched_clock_cpu() if sched_clock_stable() is
true.
Remove the duplicate test by directly calling sched_clock_cpu() and let the
static key act in this function instead.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1460385514-14700-1-git-send-email-daniel.lezcano@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Instead of checking sched_clock_stable from the nohz subsystem to verify
its tick dependency, migrate it to the new mask in order to include it
to the all-in-one check.
Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
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Pull workqueue update from Tejun Heo:
"Workqueue changes for v4.5. One cleanup patch and three to improve
the debuggability.
Workqueue now has a stall detector which dumps workqueue state if any
worker pool hasn't made forward progress over a certain amount of time
(30s by default) and also triggers a warning if a workqueue which can
be used in memory reclaim path tries to wait on something which can't
be.
These should make workqueue hangs a lot easier to debug."
* 'for-4.5' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
workqueue: simplify the apply_workqueue_attrs_locked()
workqueue: implement lockup detector
watchdog: introduce touch_softlockup_watchdog_sched()
workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue
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touch_softlockup_watchdog() is used to tell watchdog that scheduler
stall is expected. One group of usage is from paths where the task
may not be able to yield for a long time such as performing slow PIO
to finicky device and coming out of suspend. The other is to account
for scheduler and timer going idle.
For scheduler softlockup detection, there's no reason to distinguish
the two cases; however, workqueue lockup detector is planned and it
can use the same signals from the former group while the latter would
spuriously prevent detection. This patch introduces a new function
touch_softlockup_watchdog_sched() and convert the latter group to call
it instead. For now, it just calls touch_softlockup_watchdog() and
there's no functional difference.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
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There were still a number of references to my old Red Hat email
address in the kernel source. Remove these while keeping the
Red Hat copyright notices intact.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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When the hypervisor pauses a virtualised kernel the kernel will observe a
jump in timebase, this can cause spurious messages from the softlockup
detector.
Whilst these messages are harmless, they are accompanied with a stack
trace which causes undue concern and more problematically the stack trace
in the guest has nothing to do with the observed problem and can only be
misleading.
Futhermore, on POWER8 this is completely avoidable with the introduction
of the Virtual Time Base (VTB) register.
This patch (of 2):
This permits the use of arch specific clocks for which virtualised kernels
can use their notion of 'running' time, not the elpased wall time which
will include host execution time.
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Andrew Jones <drjones@redhat.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: chai wen <chaiw.fnst@cn.fujitsu.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: Ben Zhang <benzh@chromium.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Convert uses of __get_cpu_var for creating a address from a percpu
offset to this_cpu_ptr.
The two cases where get_cpu_var is used to actually access a percpu
variable are changed to use this_cpu_read/raw_cpu_read.
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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To increase compiler portability there is <linux/compiler.h> which
provides convenience macros for various gcc constructs. Eg: __weak for
__attribute__((weak)). I've replaced all instances of gcc attributes
with the right macro in the kernel subsystem.
Signed-off-by: Gideon Israel Dsouza <gidisrael@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Prevent tracing of preempt_disable/enable() in sched_clock_cpu().
When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are
traced and this causes trace_clock() users (and probably others) to
go into an infinite recursion. Systems with a stable sched_clock()
are not affected.
This problem is similar to that fixed by upstream commit 95ef1e52922
("KVM guest: prevent tracing recursion with kvmclock").
Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1394083528.4524.3.camel@nexus
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The code would assume sched_clock_stable() and switch to !stable
later, this switch brings a discontinuity in time.
The discontinuity on switching from stable to unstable was always
present, but previously we would set stable/unstable before
initializing TSC and usually stick to the one we start out with.
So the static_key bits brought an extra switch where there previously
wasn't one.
Things are further complicated by the fact that we cannot use
static_key as early as we usually call set_sched_clock_stable().
Fix things by tracking the stable state in a regular variable and only
set the static_key to the right state on sched_clock_init(), which is
ran right after late_time_init->tsc_init().
Before this we would not be using the TSC anyway.
Reported-and-Tested-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: dyoung@redhat.com
Fixes: 35af99e646c7 ("sched/clock, x86: Use a static_key for sched_clock_stable")
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: hpa@zytor.com
Cc: paulmck@linux.vnet.ibm.com
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Cc: rjw@rjwysocki.net
Cc: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Cc: rui.zhang@intel.com
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140122115918.GG3694@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The below tells us the static_key conversion has a problem; since the
exact point of clearing that flag isn't too important, delay the flip
and use a workqueue to process it.
[ ] TSC synchronization [CPU#0 -> CPU#22]:
[ ] Measured 8 cycles TSC warp between CPUs, turning off TSC clock.
[ ]
[ ] ======================================================
[ ] [ INFO: possible circular locking dependency detected ]
[ ] 3.13.0-rc3-01745-g848b0d0322cb-dirty #637 Not tainted
[ ] -------------------------------------------------------
[ ] swapper/0/1 is trying to acquire lock:
[ ] (jump_label_mutex){+.+...}, at: [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]
[ ] but task is already holding lock:
[ ] (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] which lock already depends on the new lock.
[ ]
[ ]
[ ] the existing dependency chain (in reverse order) is:
[ ]
[ ] -> #1 (cpu_hotplug.lock){+.+.+.}:
[ ] [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ] [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ] [<ffffffff81093fdc>] get_online_cpus+0x3c/0x60
[ ] [<ffffffff8104cc67>] arch_jump_label_transform+0x37/0x130
[ ] [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ] [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ] [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ] [<ffffffff810c0f65>] sched_feat_set+0xf5/0x100
[ ] [<ffffffff810c5bdc>] set_numabalancing_state+0x2c/0x30
[ ] [<ffffffff81d12f3d>] numa_policy_init+0x1af/0x1b7
[ ] [<ffffffff81cebdf4>] start_kernel+0x35d/0x41f
[ ] [<ffffffff81ceb5a5>] x86_64_start_reservations+0x2a/0x2c
[ ] [<ffffffff81ceb6a2>] x86_64_start_kernel+0xfb/0xfe
[ ]
[ ] -> #0 (jump_label_mutex){+.+...}:
[ ] [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ] [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ] [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ] [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ] [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ] [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ] [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ] [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ] [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ] [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ] [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ] [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ] [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ] [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ] [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]
[ ] other info that might help us debug this:
[ ]
[ ] Possible unsafe locking scenario:
[ ]
[ ] CPU0 CPU1
[ ] ---- ----
[ ] lock(cpu_hotplug.lock);
[ ] lock(jump_label_mutex);
[ ] lock(cpu_hotplug.lock);
[ ] lock(jump_label_mutex);
[ ]
[ ] *** DEADLOCK ***
[ ]
[ ] 2 locks held by swapper/0/1:
[ ] #0: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff81094037>] cpu_maps_update_begin+0x17/0x20
[ ] #1: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] stack backtrace:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ] ffffffff82c9c270 ffff880236843bb8 ffffffff8165c5f5 ffffffff82c9c270
[ ] ffff880236843bf8 ffffffff81658c02 ffff880236843c80 ffff8802368586a0
[ ] ffff880236858678 0000000000000001 0000000000000002 ffff880236858000
[ ] Call Trace:
[ ] [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ] [<ffffffff81658c02>] print_circular_bug+0x1f9/0x207
[ ] [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ] [<ffffffff816680ff>] ? __atomic_notifier_call_chain+0x8f/0xb0
[ ] [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ] [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ] [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ] [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ] [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ] [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ] [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ] [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ] [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ] [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ] [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ] [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ] [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ] [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ] [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ] [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ------------[ cut here ]------------
[ ] WARNING: CPU: 0 PID: 1 at /usr/src/linux-2.6/kernel/smp.c:374 smp_call_function_many+0xad/0x300()
[ ] Modules linked in:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ] 0000000000000009 ffff880236843be0 ffffffff8165c5f5 0000000000000000
[ ] ffff880236843c18 ffffffff81093d8c 0000000000000000 0000000000000000
[ ] ffffffff81ccd1a0 ffffffff810ca951 0000000000000000 ffff880236843c28
[ ] Call Trace:
[ ] [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ] [<ffffffff81093d8c>] warn_slowpath_common+0x8c/0xc0
[ ] [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ] [<ffffffff81093dda>] warn_slowpath_null+0x1a/0x20
[ ] [<ffffffff8110b72d>] smp_call_function_many+0xad/0x300
[ ] [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ] [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ] [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ] [<ffffffff8110ba96>] smp_call_function+0x46/0x80
[ ] [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ] [<ffffffff8110bb3c>] on_each_cpu+0x3c/0xa0
[ ] [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ] [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ] [<ffffffff8104f964>] text_poke_bp+0x64/0xd0
[ ] [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ] [<ffffffff8104ccde>] arch_jump_label_transform+0xae/0x130
[ ] [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ] [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ] [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ] [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ] [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ] [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ] [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ] [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ] [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ] [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ] [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ] [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ---[ end trace 6ff1df5620c49d26 ]---
[ ] tsc: Marking TSC unstable due to check_tsc_sync_source failed
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-v55fgqj3nnyqnngmvuu8ep6h@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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In order to avoid the runtime condition and variable load turn
sched_clock_stable into a static_key.
Also provide a shorter implementation of local_clock() and
cpu_clock(int) when sched_clock_stable==1.
MAINLINE PRE POST
sched_clock_stable: 1 1 1
(cold) sched_clock: 329841 221876 215295
(cold) local_clock: 301773 234692 220773
(warm) sched_clock: 38375 25602 25659
(warm) local_clock: 100371 33265 27242
(warm) rdtsc: 27340 24214 24208
sched_clock_stable: 0 0 0
(cold) sched_clock: 382634 235941 237019
(cold) local_clock: 396890 297017 294819
(warm) sched_clock: 38194 25233 25609
(warm) local_clock: 143452 71234 71232
(warm) rdtsc: 27345 24245 24243
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-eummbdechzz37mwmpags1gjr@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Now that x86 no longer requires IRQs disabled for sched_clock() and
ia64 never had this requirement (it doesn't seem to do cpufreq at
all), we can remove the requirement of disabling IRQs.
MAINLINE PRE POST
sched_clock_stable: 1 1 1
(cold) sched_clock: 329841 257223 221876
(cold) local_clock: 301773 309889 234692
(warm) sched_clock: 38375 25280 25602
(warm) local_clock: 100371 85268 33265
(warm) rdtsc: 27340 24247 24214
sched_clock_stable: 0 0 0
(cold) sched_clock: 382634 301224 235941
(cold) local_clock: 396890 399870 297017
(warm) sched_clock: 38194 25630 25233
(warm) local_clock: 143452 129629 71234
(warm) rdtsc: 27345 24307 24245
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/n/tip-36e5kohiasnr106d077mgubp@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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The sched_clock_remote() implementation has the following inatomicity
problem on 32bit systems when accessing the remote scd->clock, which
is a 64bit value.
CPU0 CPU1
sched_clock_local() sched_clock_remote(CPU0)
...
remote_clock = scd[CPU0]->clock
read_low32bit(scd[CPU0]->clock)
cmpxchg64(scd->clock,...)
read_high32bit(scd[CPU0]->clock)
While the update of scd->clock is using an atomic64 mechanism, the
readout on the remote cpu is not, which can cause completely bogus
readouts.
It is a quite rare problem, because it requires the update to hit the
narrow race window between the low/high readout and the update must go
across the 32bit boundary.
The resulting misbehaviour is, that CPU1 will see the sched_clock on
CPU1 ~4 seconds ahead of it's own and update CPU1s sched_clock value
to this bogus timestamp. This stays that way due to the clamping
implementation for about 4 seconds until the synchronization with
CLOCK_MONOTONIC undoes the problem.
The issue is hard to observe, because it might only result in a less
accurate SCHED_OTHER timeslicing behaviour. To create observable
damage on realtime scheduling classes, it is necessary that the bogus
update of CPU1 sched_clock happens in the context of an realtime
thread, which then gets charged 4 seconds of RT runtime, which results
in the RT throttler mechanism to trigger and prevent scheduling of RT
tasks for a little less than 4 seconds. So this is quite unlikely as
well.
The issue was quite hard to decode as the reproduction time is between
2 days and 3 weeks and intrusive tracing makes it less likely, but the
following trace recorded with trace_clock=global, which uses
sched_clock_local(), gave the final hint:
<idle>-0 0d..30 400269.477150: hrtimer_cancel: hrtimer=0xf7061e80
<idle>-0 0d..30 400269.477151: hrtimer_start: hrtimer=0xf7061e80 ...
irq/20-S-587 1d..32 400273.772118: sched_wakeup: comm= ... target_cpu=0
<idle>-0 0dN.30 400273.772118: hrtimer_cancel: hrtimer=0xf7061e80
What happens is that CPU0 goes idle and invokes
sched_clock_idle_sleep_event() which invokes sched_clock_local() and
CPU1 runs a remote wakeup for CPU0 at the same time, which invokes
sched_remote_clock(). The time jump gets propagated to CPU0 via
sched_remote_clock() and stays stale on both cores for ~4 seconds.
There are only two other possibilities, which could cause a stale
sched clock:
1) ktime_get() which reads out CLOCK_MONOTONIC returns a sporadic
wrong value.
2) sched_clock() which reads the TSC returns a sporadic wrong value.
#1 can be excluded because sched_clock would continue to increase for
one jiffy and then go stale.
#2 can be excluded because it would not make the clock jump
forward. It would just result in a stale sched_clock for one jiffy.
After quite some brain twisting and finding the same pattern on other
traces, sched_clock_remote() remained the only place which could cause
such a problem and as explained above it's indeed racy on 32bit
systems.
So while on 64bit systems the readout is atomic, we need to verify the
remote readout on 32bit machines. We need to protect the local->clock
readout in sched_clock_remote() on 32bit as well because an NMI could
hit between the low and the high readout, call sched_clock_local() and
modify local->clock.
Thanks to Siegfried Wulsch for bearing with my debug requests and
going through the tedious tasks of running a bunch of reproducer
systems to generate the debug information which let me decode the
issue.
Reported-by: Siegfried Wulsch <Siegfried.Wulsch@rovema.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1304051544160.21884@ionos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
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There's too many sched*.[ch] files in kernel/, give them their own
directory.
(No code changed, other than Makefile glue added.)
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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