From: Oleg Nesterov <oleg@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>,
David Howells <dhowells@redhat.com>,
David Miller <davem@davemloft.net>
Cc: Serge Hallyn <serue@us.ibm.com>,
Steve Dickson <steved@redhat.com>,
Trond Myklebust <Trond.Myklebust@netapp.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Daire Byrne <Daire.Byrne@framestore.com>,
linux-kernel@vger.kernel.org
Subject: [PATCH] slow_work_execute() needs mb() before test_bit(SLOW_WORK_PENDING)
Date: Mon, 13 Apr 2009 22:13:06 +0200 [thread overview]
Message-ID: <20090413201306.GA16653@redhat.com> (raw)
slow_work_execute:
clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
if (test_bit(SLOW_WORK_PENDING, &work->flags) {
clear_bit_unlock() implies release semantics, iow we have a one-way barrier
before clear_bit(). But we need the mb() semantics after clear_bit(), before
we test SLOW_WORK_PENDING. Otherwise we can miss SLOW_WORK_ENQ_DEFERRED if
we race slow_work_enqueue().
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
--- 6.30/kernel/slow-work.c~2_BITS_MB 2009-04-13 19:40:20.000000000 +0200
+++ 6.30/kernel/slow-work.c 2009-04-13 21:19:33.000000000 +0200
@@ -198,7 +198,8 @@ static bool slow_work_execute(void)
if (very_slow)
atomic_dec(&vslow_work_executing_count);
- clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
+ clear_bit(SLOW_WORK_EXECUTING, &work->flags);
+ smp_mb__after_clear_bit();
/* if someone tried to enqueue the item whilst we were executing it,
* then it'll be left unenqueued to avoid multiple threads trying to
next reply other threads:[~2009-04-13 20:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-13 20:13 Oleg Nesterov [this message]
2009-04-13 20:13 ` [PATCH] slow_work_execute() needs mb() before test_bit(SLOW_WORK_PENDING) Oleg Nesterov
2009-04-13 21:47 ` David Howells
2009-04-13 22:02 ` Oleg Nesterov
2009-04-16 9:43 ` David Howells
2009-04-16 14:15 ` Oleg Nesterov
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