From: Peter Zijlstra <peterz@infradead.org>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>,
LKMM Maintainers -- Akira Yokosawa <akiyks@gmail.com>,
Andrea Parri <andrea.parri@amarulasolutions.com>,
Boqun Feng <boqun.feng@gmail.com>,
David Howells <dhowells@redhat.com>,
Daniel Lustig <dlustig@nvidia.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Kernel development list <linux-kernel@vger.kernel.org>,
Luc Maranget <luc.maranget@inria.fr>,
Alan Stern <stern@rowland.harvard.edu>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}_atomic()
Date: Tue, 23 Apr 2019 15:40:03 +0200 [thread overview]
Message-ID: <20190423134003.GV4038@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190423133010.GK3923@linux.ibm.com>
On Tue, Apr 23, 2019 at 06:30:10AM -0700, Paul E. McKenney wrote:
> There are a great many that look like this:
>
> smp_mb__before_atomic();
> clear_bit(NFSD4_CLIENT_UPCALL_LOCK, &clp->cl_flags);
> smp_mb__after_atomic();
Ooh, marvel at the comment describing the ordering there. Oh wait :-(
So much for checkpatch.pl I suppose.
I think the first is a release order for the 'LOCK' bit and the second
is because of wake_up_bit() being a shitty interface.
So maybe that should've been:
clear_bit_unlock(NFSD4_CLIENT_UPCALL_LOCK, &clp->cl_flags);
smp_mb__after_atomic();
wake_up_bit(&clp->cl_flags, NFSD4_CLIENT_UPCALL_LOCK);
instead?
next prev parent reply other threads:[~2019-04-23 13:40 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-19 17:21 [PATCH] Documentation: atomic_t.txt: Explain ordering provided by smp_mb__{before,after}_atomic() Alan Stern
2019-04-19 17:54 ` Paul E. McKenney
2019-04-19 18:00 ` Peter Zijlstra
2019-04-19 18:26 ` Paul E. McKenney
2019-04-20 0:26 ` Nicholas Piggin
2019-04-20 8:54 ` Paul E. McKenney
2019-04-23 12:17 ` Peter Zijlstra
2019-04-23 13:21 ` Paul E. McKenney
2019-04-23 13:26 ` Peter Zijlstra
2019-04-23 20:16 ` Paul E. McKenney
2019-04-23 20:28 ` Peter Zijlstra
2019-04-24 8:29 ` Paul E. McKenney
2019-04-24 8:44 ` Peter Zijlstra
2019-04-23 12:32 ` Peter Zijlstra
2019-04-23 13:30 ` Paul E. McKenney
2019-04-23 13:40 ` Peter Zijlstra [this message]
2019-04-23 20:19 ` Paul E. McKenney
2019-04-27 8:17 ` Andrea Parri
2019-04-27 8:36 ` Paul E. McKenney
2019-04-29 9:24 ` Johan Hovold
2019-04-29 14:49 ` Paul E. McKenney
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