linux-kernel - Re: [PATCH] locking/qrwlock: queued_write_lock

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Message-ID: <YJERtJD012uGlp4C@hirez.programming.kicks-ass.net>
Date:   Tue, 4 May 2021 11:19:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Will Deacon <will@...nel.org>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Ali Saidi <alisaidi@...zon.com>,
        Steve Capper <steve.capper@....com>
Subject: Re: [PATCH] locking/qrwlock: queued_write_lock_slowpath() cleanup

On Tue, Apr 27, 2021 at 08:56:59AM +0100, Will Deacon wrote:
> On Mon, Apr 26, 2021 at 02:50:17PM -0400, Waiman Long wrote:
> > Make the code more readable by replacing the atomic_cmpxchg_acquire()
> > by an equivalent atomic_try_cmpxchg_acquire() and change atomic_add()
> > to atomic_or().
> > 
> > For architectures that use qrwlock, I do not find one that has an
> > atomic_add() defined but not an atomic_or().  I guess it should be fine
> > by changing atomic_add() to atomic_or().
> > 
> > Note that the previous use of atomic_add() isn't wrong as only one
> > writer that is the wait_lock owner can set the waiting flag and the
> > flag will be cleared later on when acquiring the write lock.
> 
> Right, there's no functional change here.
> 
> > Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> > Signed-off-by: Waiman Long <longman@...hat.com>

> Acked-by: Will Deacon <will@...nel.org>

Thanks!