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Date:   Tue, 4 May 2021 11:19:48 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Will Deacon <will@kernel.org>
Cc:     Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        linux-kernel@vger.kernel.org, Borislav Petkov <bp@suse.de>,
        Ali Saidi <alisaidi@amazon.com>,
        Steve Capper <steve.capper@arm.com>
Subject: Re: [PATCH] locking/qrwlock: queued_write_lock_slowpath() cleanup
Message-ID: <YJERtJD012uGlp4C@hirez.programming.kicks-ass.net>
References: <20210426185017.19815-1-longman@redhat.com>
 <20210427075659.GA6675@willie-the-truck>
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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@linux-foundation.org>
> > Signed-off-by: Waiman Long <longman@redhat.com>

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

Thanks!