Messages in this thread | | | Date | Mon, 15 Jun 2009 11:56:06 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] atomic: Fix _atomic_dec_and_lock() deadlock on UP |
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On Mon, Jun 15, 2009 at 02:11:13PM -0400, Valerie Aurora wrote: > From: Jan Blunck <jblunck@suse.de> > > _atomic_dec_and_lock() can deadlock on UP with spinlock debugging > enabled. Currently, on UP we unconditionally spin_lock() first, which > calls __spin_lock_debug(), which takes the lock unconditionally even > on UP. This will deadlock in situations in which we call > atomic_dec_and_lock() knowing that the counter won't go to zero > (because we hold another reference) and that we already hold the lock. > Instead, we should use the SMP code path which only takes the lock if > necessary.
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Jan Blunck <jblunck@suse.de> > Signed-off-by: Valerie Aurora (Henson) <vaurora@redhat.com> > --- > lib/dec_and_lock.c | 3 +-- > 1 files changed, 1 insertions(+), 2 deletions(-) > > diff --git a/lib/dec_and_lock.c b/lib/dec_and_lock.c > index a65c314..e73822a 100644 > --- a/lib/dec_and_lock.c > +++ b/lib/dec_and_lock.c > @@ -19,11 +19,10 @@ > */ > int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock) > { > -#ifdef CONFIG_SMP > /* Subtract 1 from counter unless that drops it to 0 (ie. it was 1) */ > if (atomic_add_unless(atomic, -1, 1)) > return 0; > -#endif > + > /* Otherwise do it the slow way */ > spin_lock(lock); > if (atomic_dec_and_test(atomic)) > -- > 1.6.0.6 >
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