From: Peter Zijlstra <peterz@infradead.org>
To: Prateek Sood <prsood@codeaurora.org>
Cc: mingo@redhat.com, sramana@codeaurora.org,
linux-kernel@vger.kernel.org, Waiman Long <longman@redhat.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Andrea Parri <parri.andrea@gmail.com>
Subject: Re: [PATCH] rwsem: fix missed wakeup due to reordering of load
Date: Thu, 24 Aug 2017 13:29:27 +0200 [thread overview]
Message-ID: <20170824112927.tqejopswi7mcy4sq@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <1503487735-4362-1-git-send-email-prsood@codeaurora.org>
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()
next prev parent reply other threads:[~2017-08-24 11:29 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-23 11:28 [PATCH] rwsem: fix missed wakeup due to reordering of load Prateek Sood
2017-08-24 11:29 ` Peter Zijlstra [this message]
2017-08-24 12:33 ` Peter Zijlstra
2017-08-24 12:52 ` Peter Zijlstra
2017-09-07 14:08 ` Prateek Sood
-- strict thread matches above, loose matches on Subject: below --
2017-09-07 14:30 Prateek Sood
2017-09-19 14:05 ` Andrea Parri
2017-09-20 14:52 ` Davidlohr Bueso
2017-09-20 21:17 ` Andrea Parri
2017-09-27 21:20 ` Davidlohr Bueso
2017-09-26 18:37 ` Prateek Sood
2017-07-26 20:17 Prateek Sood
2017-07-27 15:48 ` Waiman Long
2017-07-27 16:59 ` Peter Zijlstra
2017-08-10 8:32 ` Andrea Parri
2017-08-10 10:41 ` Peter Zijlstra
2017-08-10 10:44 ` Peter Zijlstra
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