linux-kernel - Re: [lkp-robot] [btrfs] beeeccca9b: WARNING:at_mm/util.c:#kvmalloc

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Date:   Wed, 31 May 2017 08:51:28 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     kernel test robot <xiaolong.ye@...el.com>
Cc:     Vinnie Magro <vmagro@...com>, David Sterba <dsterba@...e.com>,
        Omar Sandoval <osandov@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, lkp@...org
Subject: Re: [lkp-robot] [btrfs]  beeeccca9b:
 WARNING:at_mm/util.c:#kvmalloc_node

On Wed 31-05-17 14:30:33, kernel test robot wrote:
> 
> FYI, we noticed the following commit:
> 
> commit: beeeccca9bebcec386cc31c250cff8a06cf27034 ("btrfs: Use kvzalloc instead of kzalloc/vmalloc in alloc_bitmap")
> https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git master

I have intentionally skipped alloc_bitmap because it relies on GFP_NOFS.
This doesn't work properly when falling back to vmalloc and that is what
the warning reported here says. I believe the right approach is to check
whether the GFP_NOFS is _really_ needed and document why if yes.
Otherwise drop the NOFS part in one patch with the explanation and
convert it to kvmalloc in a separate patch.

-- 
Michal Hocko
SUSE Labs