linux-kernel - Re: [PATCH] synchronize

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]

Date:	Fri, 19 Oct 2007 14:29:03 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] synchronize_irq needs a barrier


On Fri, 2007-10-19 at 12:20 +0800, Herbert Xu wrote:
> 
> That's why I think this patch is in fact the only one that
> solves all the races in this thread.  The case that it solves
> which the lock/unlock patch does not is the one where action
> flows downwards past the clearing of IRQ_INPROGRESS.  I missed
> this case earlier.
> 
> In fact this bug exists elsewhere too.  For example, the network
> stack does this in net/sched/sch_generic.c:
> 
>         /* Wait for outstanding qdisc_run calls. */
>         while (test_bit(__LINK_STATE_QDISC_RUNNING, &dev->state))
>                 yield();
> 
> This has the same problem as the current synchronize_irq code.

The network stack always made be nervous with it's bitops use as locks.
Any loop of test_bit() alone as a synchronisation method, without locks
or barriers is, imho, inherently buggy.

Ben.


-
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/