linux-kernel - Re: [PATCH] ext4: handle the rest of ext4_mb_load

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Date:   Sat, 20 May 2017 22:45:44 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] ext4: handle the rest of ext4_mb_load_buddy() ENOMEM
 errors

On Fri, May 19, 2017 at 10:09:54AM +0300, Konstantin Khlebnikov wrote:
> I've got another report about breaking ext4 by ENOMEM error returned from
> ext4_mb_load_buddy() caused by memory shortage in memory cgroup.
> This time inside ext4_discard_preallocations().
> 
> This patch replaces ext4_error() with ext4_warning() where errors returned
> from ext4_mb_load_buddy() are not fatal and handled by caller:
> * ext4_mb_discard_group_preallocations() - called before generating ENOSPC,
>   we'll try to discard other group or return ENOSPC into user-space.
> * ext4_trim_all_free() - just stop trimming and return ENOMEM from ioctl.
> 
> Some callers cannot handle errors, thus __GFP_NOFAIL is used for them:
> * ext4_discard_preallocations()
> * ext4_mb_discard_lg_preallocations()
> 
> The only unclear case is ext4_group_add_blocks(), probably ext4_std_error()
> should handle ENOMEM as warning and don't break filesystem.
> 
> Fixes: adb7ef600cc9 ("ext4: use __GFP_NOFAIL in ext4_free_blocks()")
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Thanks, applied.

					- Ted