linux-ext4 - Re: [PATCH] ext4: disable dioread_nolock whenever delayed allocation is disabled

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] [day] [month] [year] [list]

Date:   Thu, 26 Mar 2020 10:57:57 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Eric Whitney <enwlinux@...il.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: disable dioread_nolock whenever delayed allocation
 is disabled

On Thu, Mar 19, 2020 at 11:00:28AM -0400, Eric Whitney wrote:
> The patch "ext4: make dioread_nolock the default" (244adf6426ee) causes
> generic/422 to fail when run in kvm-xfstests' ext3conv test case.  This
> applies both the dioread_nolock and nodelalloc mount options, a
> combination not previously tested by kvm-xfstests.  The failure occurs
> because the dioread_nolock code path splits a previously fallocated
> multiblock extent into a series of single block extents when overwriting
> a portion of that extent.  That causes allocation of an extent tree leaf
> node and a reshuffling of extents.  Once writeback is completed, the
> individual extents are recombined into a single extent, the extent is
> moved again, and the leaf node is deleted.  The difference in block
> utilization before and after writeback due to the leaf node triggers the
> failure.
> 
> The original reason for this behavior was to avoid ENOSPC when handling
> I/O completions during writeback in the dioread_nolock code paths when
> delayed allocation is disabled.  It may no longer be necessary, because
> code was added in the past to reserve extra space to solve this problem
> when delayed allocation is enabled, and this code may also apply when
> delayed allocation is disabled.  Until this can be verified, don't use
> the dioread_nolock code paths if delayed allocation is disabled.
> 
> Signed-off-by: Eric Whitney <enwlinux@...il.com>

Applied, thanks.

						- Ted