linux-ext4 - Re: Segfaults--they're back!

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Date:	Thu, 10 Jul 2008 10:51:50 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Gary Hawco <ghawco@....net>
Cc:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Theodore Tso <tytso@....edu>, Mingming <cmm@...ibm.com>
Subject: Re: Segfaults--they're back!

On Wed, Jul 09, 2008 at 03:00:04PM +0000, Gary Hawco wrote:
> Segfaults have returned with snapshots compiled after 070908--0010hrs GMT.
> 
> That one worked fine.
> 
> The next one I tried (070908/0025hrs GMT) caused segfaults in both Gentoo &
> Slackware (a first for Slackware) when trying to untar
> linux-2.6.26-rc9.tar.bz2 tarball)
> 
> I then rolled back two snapshots to 070908/0012hrs GMT) and it segfaulted
> in both operating systems doing same untarring function.
> 
> So, apparently, since 0010snapshot
> (ext4-patch-queue-bfb23cf4cd345552c774142cb10ac1225caf35f5.tar.gz) works fine
> 
> and 0012snapshot
> (ext4-patch-queue-be66b0c5c3f4293176301c0ddcb8db95b0576cb4.tar.gz)
> segfaults, the 
> Add ext4-fix-mb_find_next_bit-return.patch must be the culprit.

Is your file system full when this happens ? Which user space call cause
the segfault ? An strace should be able to help you find that. We
actually have modified ext4 to give SIGBUS when we hit ENOSPC during
mmap write. For ex:

root:/ext4# /root/mmaptest ./test4  0 100
mmaping 0 to 100
Bus error (core dumped)
root:/ext4# 

-aneesh
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