linux-ext4 - Re: [PATCH 1/2] fs: ext4: use BUG_ON if writepage call comes from direct reclaim

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Message-ID: <20180703103948.GB27426@thunk.org>
Date:   Tue, 3 Jul 2018 06:39:48 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Yang Shi <yang.shi@...ux.alibaba.com>
Cc:     mgorman@...hsingularity.net, 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 1/2] fs: ext4: use BUG_ON if writepage call comes from
 direct reclaim

On Tue, Jul 03, 2018 at 12:11:18PM +0800, Yang Shi wrote:
> direct reclaim doesn't write out filesystem page, only kswapd could do
> it. So, if the call comes from direct reclaim, it is definitely a bug.
> 
> And, Mel Gormane also mentioned "Ultimately, this will be a BUG_ON." In
> commit 94054fa3fca1fd78db02cb3d68d5627120f0a1d4 ("xfs: warn if direct
> reclaim tries to writeback pages").
> 
> Although it is for xfs, ext4 has the similar behavior, so elevate
> WARN_ON to BUG_ON.
> 
> And, correct the comment accordingly.
> 
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: "Theodore Ts'o" <tytso@....edu>
> Cc: Andreas Dilger <adilger.kernel@...ger.ca>
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>

What's the upside of crashing the kernel if the file sytsem can handle it?

       	   	     	      	  	    - Ted