From: Jens Axboe <axboe@kernel.dk>
To: Paul Bolle <pebolle@tiscali.nl>
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 10:53:43 +0200 [thread overview]
Message-ID: <4DA2C197.1060402@kernel.dk> (raw)
In-Reply-To: <1302511553.29915.12.camel@t41.thuisdomein>
On 2011-04-11 10:45, Paul Bolle wrote:
> 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?
It's not possible, if it was then that would be the bug - someone
releasing a reference to the ioc that they do not hold. And that is what
the BUG_ON() is there to catch, not a race between two threads.
--
Jens Axboe
prev parent reply other threads:[~2011-04-11 8:53 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-10 13:41 block: ioc->refcount accessed twice in put_io_context()? Paul Bolle
2011-04-11 1:54 ` Shaohua Li
2011-04-11 7:42 ` Jens Axboe
2011-04-11 8:45 ` Paul Bolle
2011-04-11 8:53 ` Jens Axboe [this message]
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