Messages in this thread | | | Date | Tue, 14 Apr 2009 09:48:39 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] atomic: Only take lock when the counter drops to zero on UP as well |
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On Tue, Apr 14, 2009 at 08:52:39AM +0200, Nick Piggin wrote: > On Fri, Apr 10, 2009 at 06:13:57PM +0200, Jan Blunck wrote: > > I think it is wrong to unconditionally take the lock before calling > > atomic_dec_and_test() in _atomic_dec_and_lock(). This will deadlock in > > situation where it is known that the counter will not reach zero (e.g. holding > > another reference to the same object) but the lock is already taken. > > > > Signed-off-by: Jan Blunck <jblunck@suse.de> > > Paul's worry about callers aside, I think it is probably a good idea > to reduce ifdefs and share more code.
I am also OK with this patch.
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> So for this patch, > > Acked-by: Nick Piggin <npiggin@suse.de> > > > --- > > 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)) > > -- > > 1.6.0.2
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