linux-kernel - Re: [PATCH 7/9] jbd2: make the whole kjournald2 kthread NOFS safe

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Date:   Fri, 16 Dec 2016 09:40:57 +0100
From:   Jan Kara <jack@...e.cz>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Theodore Ts'o <tytso@....edu>, Chris Mason <clm@...com>,
        David Sterba <dsterba@...e.cz>, Jan Kara <jack@...e.cz>,
        ceph-devel@...r.kernel.org, cluster-devel@...hat.com,
        linux-nfs@...r.kernel.org, logfs@...fs.org,
        linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-mtd@...ts.infradead.org,
        reiserfs-devel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-afs@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 7/9] jbd2: make the whole kjournald2 kthread NOFS safe

On Thu 15-12-16 15:07:13, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> kjournald2 is central to the transaction commit processing. As such any
> potential allocation from this kernel thread has to be GFP_NOFS. Make
> sure to mark the whole kernel thread GFP_NOFS by the memalloc_nofs_save.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Michal Hocko <mhocko@...e.com>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/jbd2/journal.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 8ed971eeab44..6dad8c5d6ddf 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -206,6 +206,13 @@ static int kjournald2(void *arg)
>  	wake_up(&journal->j_wait_done_commit);
>  
>  	/*
> +	 * Make sure that no allocations from this kernel thread will ever recurse
> +	 * to the fs layer because we are responsible for the transaction commit
> +	 * and any fs involvement might get stuck waiting for the trasn. commit.
> +	 */
> +	memalloc_nofs_save();
> +
> +	/*
>  	 * And now, wait forever for commit wakeup events.
>  	 */
>  	write_lock(&journal->j_state_lock);
> -- 
> 2.10.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR