linux-kernel - Re: [PATCH] make lock_super recursive to simulate BKL

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Date:	Tue, 19 Aug 2008 21:14:24 -0400
From:	Bart Trojanowski <bart@...ie.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Cc:	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] make lock_super recursive to simulate BKL

* Linus Torvalds <torvalds@...ux-foundation.org> [080819 18:23]:
> 
> 
> On Tue, 19 Aug 2008, Bart Trojanowski wrote:
> >
> > This fixes a regression introduced when BKL was removed from the
> > vfat driver in commit 8f5934278d1d86590244c2791b28f77d67466007.
> 
> I agree that it's going to almost certainly fix the regression, but could 
> you test the following patch instead as an alternative? I'd rather remove 
> the broken recursive lockign than introduce it as an acceptable concept.

Looks good.  I ran 10 parallel processes creating 1M files truncating
them, writing to them again and then deleting them.  This patch fixes
the issue I ran into.

Signed-off-by: Bart Trojanowski <bart@...ie.net>

> ---
>  fs/fat/inode.c |   10 +++-------
>  1 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 6d266d7..80ff338 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -562,26 +562,23 @@ static int fat_write_inode(struct inode *inode, int wait)
>  	struct buffer_head *bh;
>  	struct msdos_dir_entry *raw_entry;
>  	loff_t i_pos;
> -	int err = 0;
> +	int err;
>  
>  retry:
>  	i_pos = MSDOS_I(inode)->i_pos;
>  	if (inode->i_ino == MSDOS_ROOT_INO || !i_pos)
>  		return 0;
>  
> -	lock_super(sb);
>  	bh = sb_bread(sb, i_pos >> sbi->dir_per_block_bits);
>  	if (!bh) {
>  		printk(KERN_ERR "FAT: unable to read inode block "
>  		       "for updating (i_pos %lld)\n", i_pos);
> -		err = -EIO;
> -		goto out;
> +		return -EIO;
>  	}
>  	spin_lock(&sbi->inode_hash_lock);
>  	if (i_pos != MSDOS_I(inode)->i_pos) {
>  		spin_unlock(&sbi->inode_hash_lock);
>  		brelse(bh);
> -		unlock_super(sb);
>  		goto retry;
>  	}
>  
> @@ -607,11 +604,10 @@ retry:
>  	}
>  	spin_unlock(&sbi->inode_hash_lock);
>  	mark_buffer_dirty(bh);
> +	err = 0;
>  	if (wait)
>  		err = sync_dirty_buffer(bh);
>  	brelse(bh);
> -out:
> -	unlock_super(sb);
>  	return err;
>  }
>  
> --
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