Messages in this thread | | | Date | Sat, 11 Apr 2009 10:49:05 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] atomic: Only take lock when the counter drops to zero on UP as well |
| |
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.
The thought of calling _atomic_dec_and_lock() when you already hold the lock really really scares me.
Could you please give an example where you need to do this?
Thanx, Paul
> Signed-off-by: Jan Blunck <jblunck@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 >
| |