From: Kirill Korotaev <dev@sw.ru>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: Andrew Morton <akpm@osdl.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sys_getppid oopses on debug kernel
Date: Tue, 08 Aug 2006 19:43:40 +0400 [thread overview]
Message-ID: <44D8B12C.40200@sw.ru> (raw)
In-Reply-To: <1155050817.19249.42.camel@localhost.localdomain>
> Accessing freed memory is a bug, always, not just *only* when slab
> debugging is on, right? Doesn't this mean we could get junk, or that
> the reader could potentially run off a bad pointer?
no, read the comment in sys_getppid.
It is a valid optimization. _safe_ and alowing to bypass taking the lock.
BUT! This optimization relies on the fact that kernel memory (DMA + normal zone)
is always mapped into virtual address space.
Which is invalid for debug kernels only.
> It seems that this patch only papers over the problem in the case when
> it is observed, but doesn't really even fix the normal case.
>
> Could we use a seqlock to determine when real_parent is in flux, and
> re-read real_parent until we get a consistent one? We could use in in
> lieu of the existing for() loop.
Kirill
next prev parent reply other threads:[~2006-08-08 15:43 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-08-08 10:22 [PATCH] sys_getppid oopses on debug kernel Kirill Korotaev
2006-08-08 15:26 ` Dave Hansen
2006-08-08 15:34 ` Björn Steinbrink
2006-08-08 15:41 ` Dave Hansen
2006-08-08 15:43 ` Kirill Korotaev [this message]
2006-08-08 15:49 ` Dave Hansen
2006-08-08 15:54 ` Kirill Korotaev
2006-08-08 15:58 ` Martin Schwidefsky
2006-08-09 3:09 ` Andi Kleen
2006-08-09 3:31 ` Andrew Morton
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