diff options
| author | Tony Breeds <tony@bakeyournoodle.com> | 2010-05-19 15:46:36 +1000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-07-05 11:15:33 -0700 |
| commit | 59385efa61f29199c726fe474ff353000695b03b (patch) | |
| tree | 7bf9188c7ad0bc1677ae850bc3857dce61f0b79f /kernel | |
| parent | 3232ce8f86728d49deea779c45f8447fe1aef2eb (diff) | |
mutex: Fix optimistic spinning vs. BKL
commit fd6be105b883244127a734ac9f14ae94a022dcc0 upstream.
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>
LKML-Reference: <20100519054636.GC12389@ozlabs.org>
[ added an unlikely() attribute to the branch ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'kernel')
| -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. */ |