Messages in this thread | | | Date | Thu, 24 Aug 2017 13:29:27 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] rwsem: fix missed wakeup due to reordering of load |
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WTH did you not Cc the people that commented on your patch last time?
On Wed, Aug 23, 2017 at 04:58:55PM +0530, Prateek Sood wrote: > If a spinner is present, there is a chance that the load of > rwsem_has_spinner() in rwsem_wake() can be reordered with > respect to decrement of rwsem count in __up_write() leading > to wakeup being missed.
> spinning writer up_write caller > --------------- ----------------------- > [S] osq_unlock() [L] osq > spin_lock(wait_lock) > sem->count=0xFFFFFFFF00000001 > +0xFFFFFFFF00000000 > count=sem->count > MB > sem->count=0xFFFFFFFE00000001 > -0xFFFFFFFF00000001 > RMB
This doesn't make sense, it appears to order a STORE against something else.
> spin_trylock(wait_lock) > return > rwsem_try_write_lock(count) > spin_unlock(wait_lock) > schedule()
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