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| author | Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> | 2012-10-08 16:28:20 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-10-09 16:22:15 +0900 |
| commit | 075663d19885eb3738fd2d7dbdb8947e12563b68 (patch) | |
| tree | 99454962711f19b24b5b4642b6a95a6551731228 /kernel/cpu.c | |
| parent | 7ac57a89de958fbb5271dc504d0c25e34dbeec32 (diff) | |
| download | linux-075663d19885eb3738fd2d7dbdb8947e12563b68.tar.gz linux-075663d19885eb3738fd2d7dbdb8947e12563b68.tar.bz2 linux-075663d19885eb3738fd2d7dbdb8947e12563b68.zip | |
CPU hotplug, debug: detect imbalance between get_online_cpus() and put_online_cpus()
The synchronization between CPU hotplug readers and writers is achieved
by means of refcounting, safeguarded by the cpu_hotplug.lock.
get_online_cpus() increments the refcount, whereas put_online_cpus()
decrements it. If we ever hit an imbalance between the two, we end up
compromising the guarantees of the hotplug synchronization i.e, for
example, an extra call to put_online_cpus() can end up allowing a
hotplug reader to execute concurrently with a hotplug writer.
So, add a WARN_ON() in put_online_cpus() to detect such cases where the
refcount can go negative, and also attempt to fix it up, so that we can
continue to run.
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cpu.c')
| -rw-r--r-- | kernel/cpu.c | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c index f560598807c1..42bd331ee0ab 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -80,6 +80,10 @@ void put_online_cpus(void) if (cpu_hotplug.active_writer == current) return; mutex_lock(&cpu_hotplug.lock); + + if (WARN_ON(!cpu_hotplug.refcount)) + cpu_hotplug.refcount++; /* try to fix things up */ + if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) wake_up_process(cpu_hotplug.active_writer); mutex_unlock(&cpu_hotplug.lock); |