Messages in this thread | | | Subject | Re: [PATCH 2/3] rwsem: Implement down_read_interruptible | From | Waiman Long <> | Date | Mon, 7 Dec 2020 14:02:25 -0500 |
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On 12/7/20 11:58 AM, David Laight wrote: > From: Waiman Long >> Sent: 07 December 2020 15:34 >> >> On 12/7/20 4:02 AM, Peter Zijlstra wrote: >>> On Thu, Dec 03, 2020 at 08:59:13PM -0500, Waiman Long wrote: >>>> On 12/3/20 3:11 PM, Eric W. Biederman wrote: >>>>> +static inline int __down_read_interruptible(struct rw_semaphore *sem) >>>>> +{ >>>>> + if (!rwsem_read_trylock(sem)) { >>>>> + if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE))) >>>>> + return -EINTR; >>>>> + DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem); >>>>> + } else { >>>>> + rwsem_set_reader_owned(sem); >>>>> + } >>>>> + return 0; >>>>> +} >>>>> + >>>>> static inline int __down_read_killable(struct rw_semaphore *sem) >>>>> { >>>>> if (!rwsem_read_trylock(sem)) { >>>>> @@ -1495,6 +1507,20 @@ void __sched down_read(struct rw_semaphore *sem) >>>>> } >>>>> EXPORT_SYMBOL(down_read); >>>>> +int __sched down_read_interruptible(struct rw_semaphore *sem) >>>>> +{ >>>>> + might_sleep(); >>>>> + rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_); >>>>> + >>>>> + if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) { >>>>> + rwsem_release(&sem->dep_map, _RET_IP_); >>>>> + return -EINTR; >>>>> + } >>>>> + >>>>> + return 0; >>>>> +} >>>>> +EXPORT_SYMBOL(down_read_interruptible); >>>>> + >>>>> int __sched down_read_killable(struct rw_semaphore *sem) >>>>> { >>>>> might_sleep(); >>>> Acked-by: Waiman Long <longman@redhat.com> >>> Yeah, that seems correct.. There's an unfortunate amount of copy-paste >>> there though. >>> >>> Do we want to follow that up with something like this? >> I am actually thinking about similar streamlining once the patch lands. >> >> Your suggested changes look fine to me. > How much more difficult would it be to also add a timeout option? > I looked at adding one to the mutex code - and fell into a big pile > of replicated code. > > ISTM that one the initial locked exchange (and spin) fails a few > extra instructions when heading for the sleep don't really matter > Actually, I had tried that before. See
https://lore.kernel.org/lkml/20190911150537.19527-1-longman@redhat.com/
That is for rwsem, but the same can be done for mutex. However, Peter didn't seem to like the idea of a timeout parameter. Anyway, it is certainly doable if there is a good use case for it.
Cheers, Longman
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