From: Paul Bolle <pebolle@tiscali.nl>
To: Jens Axboe <axboe@kernel.dk>
Cc: Shaohua Li <shli@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: block: ioc->refcount accessed twice in put_io_context()?
Date: Mon, 11 Apr 2011 10:45:24 +0200 [thread overview]
Message-ID: <1302511553.29915.12.camel@t41.thuisdomein> (raw)
In-Reply-To: <4DA2B0FB.8020302@kernel.dk>
On Mon, 2011-04-11 at 09:42 +0200, Jens Axboe wrote:
> Indeed, there is nothing wrong with having the BUG_ON() there first and
> doing the decrement later.
But what makes sure then that refcount doesn't get decremented by
something else just before the atomic_long_dec_and_test() call. Eg:
Thread 1 Thread 2
======== ========
BUG_ON()
BUG_ON()
atomic_long_dec_and_test()
atomic_long_dec_and_test()
/* refcount drops to -1 here */
Or is this not possible?
> If the BUG_ON() is hit, then it's not a race
> conditon - it's a plain bug in the code.
I haven't hit that BUG_ON(), I'm just wondering why an atomic variable
is accessed twice in the same function.
Paul Bolle
next prev parent reply other threads:[~2011-04-11 8:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-10 13:41 Paul Bolle
2011-04-11 1:54 ` Shaohua Li
2011-04-11 7:42 ` Jens Axboe
2011-04-11 8:45 ` Paul Bolle [this message]
2011-04-11 8:53 ` Jens Axboe
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