Re: [PATCH v3 1/2] locking/rwsem: Add a new RWSEM_ANONYMOUSLY_OWNED flag
From: Waiman Long
Date: Tue May 15 2018 - 13:56:42 EST
On 05/15/2018 01:55 PM, Peter Zijlstra wrote:
> On Tue, May 15, 2018 at 01:52:06PM -0400, Waiman Long wrote:
>> On 05/15/2018 01:48 PM, Peter Zijlstra wrote:
>>> On Tue, May 15, 2018 at 01:38:03PM -0400, Waiman Long wrote:
>>>> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
>>>> index 30465a2..b7208e1 100644
>>>> --- a/kernel/locking/rwsem.c
>>>> +++ b/kernel/locking/rwsem.c
>>>> @@ -130,7 +130,8 @@ void up_read(struct rw_semaphore *sem)
>>>> void up_write(struct rw_semaphore *sem)
>>>> rwsem_release(&sem->dep_map, 1, _RET_IP_);
>>>> - DEBUG_RWSEMS_WARN_ON(sem->owner != current);
>>>> + DEBUG_RWSEMS_WARN_ON((sem->owner != current) &&
>>>> + !rwsem_has_anonymous_owner(sem->owner));
>>> Why? Don't we always do percpu_rwsem_acquire() before up?
>> This is to allow an unlock to happen in the unknown owner state. Yes, it
>> is not necessary to fix the percpu-rwsem problem. It is there just in
>> case a rwsem will be released in that state in the future.
> Let's not allow that until there's a very good reason for it.
Sure. I can remove that.