linux-kernel - Re: [PATCH v2 0/2] Fix generic/390 failure due to quota release after freeze

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Message-ID: <Zz8sA7YavAg8+mqI@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date: Thu, 21 Nov 2024 18:18:03 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: linux-ext4@...r.kernel.org, Jan Kara <jack@...e.com>
Cc: Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH v2 0/2] Fix generic/390 failure due to quota release
 after freeze

On Thu, Nov 21, 2024 at 06:08:53PM +0530, Ojaswin Mujoo wrote:
> Changes since v1:

Forgot to link v1:

https://lore.kernel.org/linux-ext4/20241115183449.2058590-1-ojaswin@linux.ibm.com/T/#t

> 
>  * Patch 1: Move flush_delayed_work() to start of function
>  * Patch 2: Guard ext4_release_dquot against freeze
> 
> Regarding patch 2, as per my understanding of the journalling code,
> right now ext4_release_dquot() can only be called from the
> quota_realease_work workqueue and hence ideally should never have a
> journal open but to future-proof it we make sure the journal is not
> opened when calling sb_start_inwrite().
> 
> ** Original Cover **
> 
> Recently we noticed generic/390 failing on powerpc systems. This test
> basically does a freeze-unfreeze loop in parallel with fsstress on the
> FS to detect any races in the code paths.
> 
> We noticed that the test started failing due to kernel WARN_ONs because
> quota_release_work workqueue started executing while the FS was frozen
> which led to creating new transactions in ext4_release_quota. 
> 
> Most of the details are in the bug however I'd just like to add that
> I'm completely new to quota code so the patch, although fixing the
> issue, might be not be logically the right thing to do. So reviews and
> suggestions are welcome. 
> 
> Also, I can only replicate this race on one of my machines reliably and
> does not appear on others.  I've tested with with fstests -g quota and
> don't see any new failures.
> 
> Ojaswin Mujoo (2):
>   quota: flush quota_release_work upon quota writeback
>   ext4: protect ext4_release_dquot against freezing
> 
>  fs/ext4/super.c  | 17 +++++++++++++++++
>  fs/quota/dquot.c |  2 ++
>  2 files changed, 19 insertions(+)
> 
> -- 
> 2.43.5
>