linux-kernel - Re: __link_block_group uses GFP

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Date:   Fri, 24 Mar 2017 19:13:40 -0400
From:   Jeff Mahoney <jeffm@...e.com>
To:     Denis Kirjanov <dkirjanov@...udlinux.com>,
        linux-btrfs@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, chris.mason@...ionio.com
Subject: Re: __link_block_group uses GFP_KERNEL

On 3/24/17 5:02 AM, Denis Kirjanov wrote:
> Hi guys,
> 
> Looks like that current code does GFP_KERNEL allocation inside
> __link_block_group.
> the function invokes kobject_add and internally creates sysfs files
> with the GFP_KERNEL flag set.

Yep, that's a bug.

> But since do_chunk_alloc executes insides the btrfs transaction it's
> not allowed to sleep.

It's allowed to sleep but isn't allowed to do reclaim that involves file
system writeback.  Michal Hocko's allocation context idea would fix
this, but it's not there yet, so we'll need to defer the kobject_add
until we can use GFP_KERNEL.

-Jeff

-- 
Jeff Mahoney
SUSE Labs



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