linux-kernel - Re: block: ioc->refcount accessed twice in put_io

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1302511553.29915.12.camel@t41.thuisdomein>
Date:	Mon, 11 Apr 2011 10:45:24 +0200
From:	Paul Bolle <pebolle@...cali.nl>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: block: ioc->refcount accessed twice in put_io_context()?

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/