From: Andrea Arcangeli <andrea@suse.de>
To: V Ganesh <ganesh@veritas.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: beware of add_waitqueue/waitqueue_active
Date: Thu, 30 Nov 2000 22:27:25 +0100 [thread overview]
Message-ID: <20001130222725.F18804@athlon.random> (raw)
In-Reply-To: <200011301332.TAA00277@vxindia.veritas.com>
In-Reply-To: <200011301332.TAA00277@vxindia.veritas.com>; from ganesh@veritas.com on Thu, Nov 30, 2000 at 07:02:56PM +0530
On Thu, Nov 30, 2000 at 07:02:56PM +0530, V Ganesh wrote:
> 3. add_wait_queue adds this process to the waitqueue. but all the writes
> are in write-buffers and have not gone down to cache/memory yet.
> 4. PageLocked() finds that the page is locked.
Right.
> [..] speculative execution
> of PageLocked() even before add_wait_queue returns [..]
Right.
Both could happen because of the new spin_unlock implementation that doesn't
take anymore the lock on the bus:
#define spin_unlock_string \
"movb $1,%0"
With the previous `lock ; btrl' 4) couldn't happen with pending
writes on the write buffer because spin_unlock was a full barrier too...
Alpha was safe because it has to imply an mb() in spin_unlock (but
sparc64 was hurted too for example).
As you say the problematic construct is not used anymore into 2.4.0-test12-pre2
in filemap.c so such deadlock can't happen anymore but it's been useful that
you pointing out the problem, thanks.
Andrea
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prev parent reply other threads:[~2000-11-30 21:58 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2000-11-30 13:32 beware of add_waitqueue/waitqueue_active V Ganesh
2000-11-30 21:27 ` Andrea Arcangeli [this message]
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