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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=44D8B12C.40200@sw.ru \
--to=dev@sw.ru \
--cc=akpm@osdl.org \
--cc=haveblue@us.ibm.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.