linux-kernel - Re: [PATCH 3/4] move rwsem_release() from sb_wait_write() to freeze

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Date:	Tue, 21 Jul 2015 10:40:47 +0200
From:	Jan Kara <jack@...e.cz>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] move rwsem_release() from sb_wait_write() to
 freeze_super()

On Mon 20-07-15 19:01:06, Oleg Nesterov wrote:
> Move the "fool the lockdep" code from sb_wait_write() into the new
> simple helper, sb_lockdep_release(), called once before return from
> freeze_super().
> 
> This is preparation, but imo this makes sense in any case. This way
> we do not hide from lockdep the "write" locks we hold when we call
> s_op->freeze_fs(sb).
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Good. You can add:

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

								Honza

> ---
>  fs/super.c |   16 ++++++++++------
>  1 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index d0fdd49..e7ea9f1 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -1236,16 +1236,10 @@ static void sb_wait_write(struct super_block *sb, int level)
>  {
>  	s64 writers;
>  
> -	/*
> -	 * We just cycle-through lockdep here so that it does not complain
> -	 * about returning with lock to userspace
> -	 */
>  	rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
> -	rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
>  
>  	do {
>  		DEFINE_WAIT(wait);
> -
>  		/*
>  		 * We use a barrier in prepare_to_wait() to separate setting
>  		 * of frozen and checking of the counter
> @@ -1261,6 +1255,14 @@ static void sb_wait_write(struct super_block *sb, int level)
>  	} while (writers);
>  }
>  
> +static void sb_freeze_release(struct super_block *sb)
> +{
> +	int level;
> +	/* Avoid the warning from lockdep_sys_exit() */
> +	for (level = 0; level < SB_FREEZE_LEVELS; ++level)
> +		rwsem_release(sb->s_writers.lock_map + level, 1, _THIS_IP_);
> +}
> +
>  /**
>   * freeze_super - lock the filesystem and force it into a consistent state
>   * @sb: the super to lock
> @@ -1349,6 +1351,7 @@ int freeze_super(struct super_block *sb)
>  			sb->s_writers.frozen = SB_UNFROZEN;
>  			smp_wmb();
>  			wake_up(&sb->s_writers.wait_unfrozen);
> +			sb_freeze_release(sb);
>  			deactivate_locked_super(sb);
>  			return ret;
>  		}
> @@ -1358,6 +1361,7 @@ int freeze_super(struct super_block *sb)
>  	 * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
>  	 */
>  	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
> +	sb_freeze_release(sb);
>  	up_write(&sb->s_umount);
>  	return 0;
>  }
> -- 
> 1.5.5.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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