linux-kernel - Re: [PATCH v5] xfs: Fix false positive lockdep warning with sb_internal & fs

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Message-ID: <20200703010720.GH5369@dread.disaster.area>
Date:   Fri, 3 Jul 2020 11:07:20 +1000
From:   Dave Chinner <david@...morbit.com>
To:     Waiman Long <longman@...hat.com>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        Qian Cai <cai@....pw>, Eric Sandeen <sandeen@...hat.com>
Subject: Re: [PATCH v5] xfs: Fix false positive lockdep warning with
 sb_internal & fs_reclaim

On Wed, Jul 01, 2020 at 08:59:23PM -0400, Waiman Long wrote:
> Suggested-by: Dave Chinner <david@...morbit.com>
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  fs/xfs/xfs_super.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 379cbff438bc..dcc97bad950a 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -913,11 +913,21 @@ xfs_fs_freeze(
>  	struct super_block	*sb)
>  {
>  	struct xfs_mount	*mp = XFS_M(sb);
> +	unsigned long		pflags;
> +	int			ret;
>  
> +	/*
> +	 * Disable fs reclaim in memory allocation for fs freeze to avoid
> +	 * causing a possible circular locking dependency lockdep splat
> +	 * relating to fs reclaim.
> +	 */

	/*
	 * The filesystem is now frozen far enough that memory reclaim
	 * cannot safely operate on the filesystem. Hence we need to
	 * set a GFP_NOFS context here to avoid recursion deadlocks.
	 */

> +	current_set_flags_nested(&pflags, PF_MEMALLOC_NOFS);

memalloc_nofs_save/restore(), please.

-Dave.
-- 
Dave Chinner
david@...morbit.com