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author | Tony Breeds <tony@bakeyournoodle.com> | 2010-05-19 15:46:36 +1000 |
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committer | Ingo Molnar <mingo@elte.hu> | 2010-05-19 08:18:44 +0200 |
commit | fd6be105b883244127a734ac9f14ae94a022dcc0 (patch) | |
tree | 9fc86c2827813379274522bdc92dd71538d207e5 /kernel/mutex.c | |
parent | 537b60d17894b7c19a6060feae40299d7109d6e7 (diff) | |
download | linux-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.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/mutex.c b/kernel/mutex.c index 632f04c57d82..4c0b7b3e6d2e 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. */ |