Messages in this thread | | | Subject | Re: [PATCH v5 1/6] rwsem: check the lock before cpmxchg in down_write_trylock | From | Tim Chen <> | Date | Tue, 24 Sep 2013 16:30:19 -0700 |
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On Tue, 2013-09-24 at 16:22 -0700, Jason Low wrote: > Should we do something similar with __down_read_trylock, such as > the following? > > > Signed-off-by: Jason Low <jason.low2@hp.com> > --- > include/asm-generic/rwsem.h | 3 +++ > 1 files changed, 3 insertions(+), 0 deletions(-) > > diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h > index bb1e2cd..47990dc 100644 > --- a/include/asm-generic/rwsem.h > +++ b/include/asm-generic/rwsem.h > @@ -42,6 +42,9 @@ static inline int __down_read_trylock(struct > rw_semaphore *sem) > long tmp; > > while ((tmp = sem->count) >= 0) { > + if (sem->count != tmp) > + continue; > +
Considering that tmp has just been assigned the value of sem->count, the added if check failure is unlikely and probably not needed. We should proceed to cmpxchg below.
> if (tmp == cmpxchg(&sem->count, tmp, > tmp + RWSEM_ACTIVE_READ_BIAS)) { > return 1;
Tim
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