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authorTony Breeds <tony@bakeyournoodle.com>2010-05-19 15:46:36 +1000
committerIngo Molnar <mingo@elte.hu>2010-05-19 08:18:44 +0200
commitfd6be105b883244127a734ac9f14ae94a022dcc0 (patch)
tree9fc86c2827813379274522bdc92dd71538d207e5 /kernel/mutex.c
parent537b60d17894b7c19a6060feae40299d7109d6e7 (diff)
downloadlinaro-lsk-fd6be105b883244127a734ac9f14ae94a022dcc0.tar.gz
mutex: Fix optimistic spinning vs. BKL
Currently, we can hit a nasty case with optimistic spinning on mutexes: CPU A tries to take a mutex, while holding the BKL CPU B tried to take the BLK while holding the mutex This looks like a AB-BA scenario but in practice, is allowed and happens due to the auto-release on schedule() nature of the BKL. In that case, the optimistic spinning code can get us into a situation where instead of going to sleep, A will spin waiting for B who is spinning waiting for A, and the only way out of that loop is the need_resched() test in mutex_spin_on_owner(). This patch fixes it by completely disabling spinning if we own the BKL. This adds one more detail to the extensive list of reasons why it's a bad idea for kernel code to be holding the BKL. Signed-off-by: Tony Breeds <tony@bakeyournoodle.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: <stable@kernel.org> LKML-Reference: <20100519054636.GC12389@ozlabs.org> [ added an unlikely() attribute to the branch ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/mutex.c')
-rw-r--r--kernel/mutex.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 632f04c57d8..4c0b7b3e6d2 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -172,6 +172,13 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
struct thread_info *owner;
/*
+ * If we own the BKL, then don't spin. The owner of
+ * the mutex might be waiting on us to release the BKL.
+ */
+ if (unlikely(current->lock_depth >= 0))
+ break;
+
+ /*
* If there's an owner, wait for it to either
* release the lock or go to sleep.
*/