linux-kernel - Re: [PATCH 2/2] fs: xfs: use BUG_ON if writepage call comes from direct reclaim

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Message-ID: <20180703043738.GG2234@dastard>
Date:   Tue, 3 Jul 2018 14:37:38 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     mgorman@...hsingularity.net, tytso@....edu,
        adilger.kernel@...ger.ca, darrick.wong@...cle.com,
        dchinner@...hat.com, akpm@...ux-foundation.org,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fs: xfs: use BUG_ON if writepage call comes from
 direct reclaim

On Tue, Jul 03, 2018 at 12:11:19PM +0800, Yang Shi wrote:
> direct reclaim doesn't write out filesystem page, only kswapd could do
> this. So, if it is called from direct relaim, it is definitely a bug.
> 
> And, Mel Gorman mentioned "Ultimately, this will be a BUG_ON." in commit
> 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct reclaim
> tries to writeback pages"),
> 
> It has been many years since that commit, so it should be safe to
> elevate WARN_ON to BUG_ON now.

NACK.

The existing code warns and then handles the situation gracefully -
this is the appropriate way to handle incorrect calling contexts.
There is absolutely no good reason to panic production kernels
in situations like this.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com