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authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>2012-10-08 16:28:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-10-09 16:22:15 +0900
commit075663d19885eb3738fd2d7dbdb8947e12563b68 (patch)
tree99454962711f19b24b5b4642b6a95a6551731228 /kernel/cpu.c
parent7ac57a89de958fbb5271dc504d0c25e34dbeec32 (diff)
downloadlwn-075663d19885eb3738fd2d7dbdb8947e12563b68.tar.gz
lwn-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.c4
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);