linux-kernel - Re: __link_block_group uses GFP

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Message-ID: <CABxMtgdx_aC53bL0XAZaTCX=8P6=J_+Z5jyUSS1GyES_5zw_qA@mail.gmail.com>
Date:   Sat, 25 Mar 2017 09:48:28 +0300
From:   Denis Kirjanov <dkirjanov@...udlinux.com>
To:     Jeff Mahoney <jeffm@...e.com>
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        chris.mason@...ionio.com
Subject: Re: __link_block_group uses GFP_KERNEL

On 3/25/17, Jeff Mahoney <jeffm@...e.com> wrote:
> 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.

Ok, I see. Can you point out to the initial patchset?

Thanks!

>
> -Jeff
>
> --
> Jeff Mahoney
> SUSE Labs
>
>