cpu_stop_queue_work() checks stopper->enabled before it queues the
work, but ->enabled == T can only guarantee cpu_stop_signal_done()
if we race with cpu_down().
This is not enough for stop_two_cpus() or stop_machine(), they will
deadlock if multi_cpu_stop() won't be called by one of the target
CPU's. stop_machine/stop_cpus are fine, they rely on stop_cpus_mutex.
But stop_two_cpus() has to check cpu_active() to avoid the same race
with hotplug, and this check is very unobvious and probably not even
correct if we race with cpu_up().
Change cpu_down() pass to clear ->enabled before cpu_stopper_thread()
flushes the pending ->works and returns with KTHREAD_SHOULD_PARK set.
Note also that smpboot_thread_call() calls cpu_stop_unpark() which
sets enabled == T at CPU_ONLINE stage, so this CPU can't go away until
cpu_stopper_thread() is called at least once. This all means that if
cpu_stop_queue_work() succeeds, we know that work->fn() will be called.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: heiko.carstens@de.ibm.com
Link: http://lkml.kernel.org/r/20151008145131.GA18139@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Jiri reported a machine stuck in multi_cpu_stop() with
migrate_swap_stop() as function and with the following src,dst cpu
pairs: {11, 4} {13, 11} { 4, 13}
4 11 13
cpuM: queue(4 ,13)
*Ma
cpuN: queue(13,11)
*N Na
*M Mb
cpuO: queue(11, 4)
*O Oa
*Nb
*Ob
Where *X denotes the cpu running the queueing of cpu-X and X[ab] denotes
the first/second queued work.
You'll observe the top of the workqueue for each cpu: 4,11,13 to be work
from cpus: M, O, N resp. IOW. deadlock.
Do away with the queueing trickery and introduce lg_double_lock() to
lock both CPUs and fully serialize the stop_two_cpus() callers instead
of the partial (and buggy) serialization we have now.
Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150605153023.GH19282@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
There is a race between stop_two_cpus, and the global stop_cpus.
It is possible for two CPUs to get their stopper functions queued
"backwards" from one another, resulting in the stopper threads
getting stuck, and the system hanging. This can happen because
queuing up stoppers is not synchronized.
This patch adds synchronization between stop_cpus (a rare operation),
and stop_two_cpus.
Reported-and-Tested-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/r/20131101104146.03d1e043@annuminas.surriel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Remove get_online_cpus() usage from the scheduler; there's 4 sites that
use it:
- sched_init_smp(); where its completely superfluous since we're in
'early' boot and there simply cannot be any hotplugging.
- sched_getaffinity(); we already take a raw spinlock to protect the
task cpus_allowed mask, this disables preemption and therefore
also stabilizes cpu_online_mask as that's modified using
stop_machine. However switch to active mask for symmetry with
sched_setaffinity()/set_cpus_allowed_ptr(). We guarantee active
mask stability by inserting sync_rcu/sched() into _cpu_down.
- sched_setaffinity(); we don't appear to need get_online_cpus()
either, there's two sites where hotplug appears relevant:
* cpuset_cpus_allowed(); for the !cpuset case we use possible_mask,
for the cpuset case we hold task_lock, which is a spinlock and
thus for mainline disables preemption (might cause pain on RT).
* set_cpus_allowed_ptr(); Holds all scheduler locks and thus has
preemption properly disabled; also it already deals with hotplug
races explicitly where it releases them.
- migrate_swap(); we can make stop_two_cpus() do the heavy lifting for
us with a little trickery. By adding a sync_sched/rcu() after the
CPU_DOWN_PREPARE notifier we can provide preempt/rcu guarantees for
cpu_active_mask. Use these to validate that both our cpus are active
when queueing the stop work before we queue the stop_machine works
for take_cpu_down().
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Link: http://lkml.kernel.org/r/20131011123820.GV3081@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Introduce stop_two_cpus() in order to allow controlled swapping of two
tasks. It repurposes the stop_machine() state machine but only stops
the two cpus which we can do with on-stack structures and avoid
machine wide synchronization issues.
The ordering of CPUs is important to avoid deadlocks. If unordered then
two cpus calling stop_two_cpus on each other simultaneously would attempt
to queue in the opposite order on each CPU causing an AB-BA style deadlock.
By always having the lowest number CPU doing the queueing of works, we can
guarantee that works are always queued in the same order, and deadlocks
are avoided.
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
[ Implemented deadlock avoidance. ]
Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/r/1381141781-10992-38-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
commit 14e568e78 (stop_machine: Use smpboot threads) introduced the
following regression:
Before this commit the stopper enabled bit was set in the online
notifier.
CPU0 CPU1
cpu_up
cpu online
hotplug_notifier(ONLINE)
stopper(CPU1)->enabled = true;
...
stop_machine()
The conversion to smpboot threads moved the enablement to the wakeup
path of the parked thread. The majority of users seem to have the
following working order:
CPU0 CPU1
cpu_up
cpu online
unpark_threads()
wakeup(stopper[CPU1])
....
stopper thread runs
stopper(CPU1)->enabled = true;
stop_machine()
But Konrad and Sander have observed:
CPU0 CPU1
cpu_up
cpu online
unpark_threads()
wakeup(stopper[CPU1])
....
stop_machine()
stopper thread runs
stopper(CPU1)->enabled = true;
Now the stop machinery kicks CPU0 into the stop loop, where it gets
stuck forever because the queue code saw stopper(CPU1)->enabled ==
false, so CPU0 waits for CPU1 to enter stomp_machine, but the CPU1
stopper work got discarded due to enabled == false.
Add a pre_unpark function to the smpboot thread descriptor and call it
before waking the thread.
This fixes the problem at hand, but the stop_machine code should be
more robust. The stopper->enabled flag smells fishy at best.
Thanks to Konrad for going through a loop of debug patches and
providing the information to decode this issue.
Reported-and-tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reported-and-tested-by: Sander Eikelenboom <linux@eikelenboom.it>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1302261843240.22263@ionos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
* 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux: (230 commits)
Revert "tracing: Include module.h in define_trace.h"
irq: don't put module.h into irq.h for tracking irqgen modules.
bluetooth: macroize two small inlines to avoid module.h
ip_vs.h: fix implicit use of module_get/module_put from module.h
nf_conntrack.h: fix up fallout from implicit moduleparam.h presence
include: replace linux/module.h with "struct module" wherever possible
include: convert various register fcns to macros to avoid include chaining
crypto.h: remove unused crypto_tfm_alg_modname() inline
uwb.h: fix implicit use of asm/page.h for PAGE_SIZE
pm_runtime.h: explicitly requires notifier.h
linux/dmaengine.h: fix implicit use of bitmap.h and asm/page.h
miscdevice.h: fix up implicit use of lists and types
stop_machine.h: fix implicit use of smp.h for smp_processor_id
of: fix implicit use of errno.h in include/linux/of.h
of_platform.h: delete needless include <linux/module.h>
acpi: remove module.h include from platform/aclinux.h
miscdevice.h: delete unnecessary inclusion of module.h
device_cgroup.h: delete needless include <linux/module.h>
net: sch_generic remove redundant use of <linux/module.h>
net: inet_timewait_sock doesnt need <linux/module.h>
...
Fix up trivial conflicts (other header files, and removal of the ab3550 mfd driver) in
- drivers/media/dvb/frontends/dibx000_common.c
- drivers/media/video/{mt9m111.c,ov6650.c}
- drivers/mfd/ab3550-core.c
- include/linux/dmaengine.h
The changed files were only including linux/module.h for the
EXPORT_SYMBOL infrastructure, and nothing else. Revector them
onto the isolated export header for faster compile times.
Nothing to see here but a whole lot of instances of:
-#include <linux/module.h>
+#include <linux/export.h>
This commit is only changing the kernel dir; next targets
will probably be mm, fs, the arch dirs, etc.
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
