[PATCH] cpuset oom lock fix
The problem, reported in:
http://bugzilla.kernel.org/show_bug.cgi?id=5859
and by various other email messages and lkml posts is that the cpuset hook
in the oom (out of memory) code can try to take a cpuset semaphore while
holding the tasklist_lock (a spinlock).
One must not sleep while holding a spinlock.
The fix seems easy enough - move the cpuset semaphore region outside the
tasklist_lock region.
This required a few lines of mechanism to implement. The oom code where
the locking needs to be changed does not have access to the cpuset locks,
which are internal to kernel/cpuset.c only. So I provided a couple more
cpuset interface routines, available to the rest of the kernel, which
simple take and drop the lock needed here (cpusets callback_sem).
Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 4748b90..14bd4ec 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -274,6 +274,7 @@
show_mem();
}
+ cpuset_lock();
read_lock(&tasklist_lock);
retry:
p = select_bad_process();
@@ -284,6 +285,7 @@
/* Found nothing?!?! Either we hang forever, or we panic. */
if (!p) {
read_unlock(&tasklist_lock);
+ cpuset_unlock();
panic("Out of memory and no killable processes...\n");
}
@@ -293,6 +295,7 @@
out:
read_unlock(&tasklist_lock);
+ cpuset_unlock();
if (mm)
mmput(mm);