linux-kernel - Re: kdump: crash_kexec()-smp_send

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: <m1ipneifqv.fsf@fess.ebiederm.org>
Date:	Mon, 24 Oct 2011 08:14:16 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	holzheu@...ux.vnet.ibm.com
Cc:	Vivek Goyal <vgoyal@...hat.com>, akpm@...ux-foundation.org,
	schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: kdump: crash_kexec()-smp_send_stop() race in panic

Michael Holzheu <holzheu@...ux.vnet.ibm.com> writes:

> Hello Vivek,
>
> In our tests we ran into the following scenario:
>
> Two CPUs have called panic at the same time. The first CPU called
> crash_kexec() and the second CPU called smp_send_stop() in panic()
> before crash_kexec() finished on the first CPU. So the second CPU
> stopped the first CPU and therefore kdump failed.
>
> 1st CPU:
> panic()->crash_kexec()->mutex_trylock(&kexec_mutex)-> do kdump
>
> 2nd CPU:
> panic()->crash_kexec()->kexec_mutex already held by 1st CPU
>        ->smp_send_stop()-> stop CPU 1 (stop kdump)
>
> How should we fix this problem? One possibility could be to do
> smp_send_stop() before we call crash_kexec().
>
> What do you think?

smp_send_stop is insufficiently reliable to be used before crash_kexec.

My first reaction would be to test oops_in_progress and wait until
oops_in_progress == 1 before calling smp_send_stop.

Eric
--
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/