Re: [PATCH 2/2] kill xfs_lock_dir_and_entry

[Christoph Hellwig <hch@lst.de>]

ping^2

On Tue, May 20, 2008 at 08:36:39AM +0200, Christoph Hellwig wrote:
> ping?
> 
> On Fri, May 02, 2008 at 12:58:03PM +0200, Christoph Hellwig wrote:
> > When multiple inodes are locked in XFS it happens in order of the inode
> > number, with the everything but the first inode trylocked if any of
> > the previous inodes is in the AIL.
> > 
> > Except for the sorting of the inodes this logic is implemented in
> > xfs_lock_inodes, but also partially duplicated in xfs_lock_dir_and_entry
> > in a particularly stupid way adds a lock roundtrip if the inode ordering
> > is not optimal.
> > 
> > This patch adds a new helper xfs_lock_two_inodes that takes two inodes
> > and locks them in the most optimal way according to the above locking
> > protocol and uses it for all places that want to lock two inodes.
> > 
> > The only caller of xfs_lock_inodes is xfs_rename which might lock up to
> > four inodes.
> > 
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > 
> > Index: linux-2.6-xfs/fs/xfs/xfs_vnodeops.c
> > ===================================================================
> > --- linux-2.6-xfs.orig/fs/xfs/xfs_vnodeops.c	2008-05-02 08:30:24.000000000 +0200
> > +++ linux-2.6-xfs/fs/xfs/xfs_vnodeops.c	2008-05-02 08:30:30.000000000 +0200
> > @@ -1897,111 +1897,6 @@ std_return:
> >  }
> >  
> >  #ifdef DEBUG
> > -/*
> > - * Some counters to see if (and how often) we are hitting some deadlock
> > - * prevention code paths.
> > - */
> > -
> > -int xfs_rm_locks;
> > -int xfs_rm_lock_delays;
> > -int xfs_rm_attempts;
> > -#endif
> > -
> > -/*
> > - * The following routine will lock the inodes associated with the
> > - * directory and the named entry in the directory. The locks are
> > - * acquired in increasing inode number.
> > - *
> > - * If the entry is "..", then only the directory is locked. The
> > - * vnode ref count will still include that from the .. entry in
> > - * this case.
> > - *
> > - * There is a deadlock we need to worry about. If the locked directory is
> > - * in the AIL, it might be blocking up the log. The next inode we lock
> > - * could be already locked by another thread waiting for log space (e.g
> > - * a permanent log reservation with a long running transaction (see
> > - * xfs_itruncate_finish)). To solve this, we must check if the directory
> > - * is in the ail and use lock_nowait. If we can't lock, we need to
> > - * drop the inode lock on the directory and try again. xfs_iunlock will
> > - * potentially push the tail if we were holding up the log.
> > - */
> > -STATIC int
> > -xfs_lock_dir_and_entry(
> > -	xfs_inode_t	*dp,
> > -	xfs_inode_t	*ip)	/* inode of entry 'name' */
> > -{
> > -	int		attempts;
> > -	xfs_ino_t	e_inum;
> > -	xfs_inode_t	*ips[2];
> > -	xfs_log_item_t	*lp;
> > -
> > -#ifdef DEBUG
> > -	xfs_rm_locks++;
> > -#endif
> > -	attempts = 0;
> > -
> > -again:
> > -	xfs_ilock(dp, XFS_ILOCK_EXCL | XFS_ILOCK_PARENT);
> > -
> > -	e_inum = ip->i_ino;
> > -
> > -	xfs_itrace_ref(ip);
> > -
> > -	/*
> > -	 * We want to lock in increasing inum. Since we've already
> > -	 * acquired the lock on the directory, we may need to release
> > -	 * if if the inum of the entry turns out to be less.
> > -	 */
> > -	if (e_inum > dp->i_ino) {
> > -		/*
> > -		 * We are already in the right order, so just
> > -		 * lock on the inode of the entry.
> > -		 * We need to use nowait if dp is in the AIL.
> > -		 */
> > -
> > -		lp = (xfs_log_item_t *)dp->i_itemp;
> > -		if (lp && (lp->li_flags & XFS_LI_IN_AIL)) {
> > -			if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
> > -				attempts++;
> > -#ifdef DEBUG
> > -				xfs_rm_attempts++;
> > -#endif
> > -
> > -				/*
> > -				 * Unlock dp and try again.
> > -				 * xfs_iunlock will try to push the tail
> > -				 * if the inode is in the AIL.
> > -				 */
> > -
> > -				xfs_iunlock(dp, XFS_ILOCK_EXCL);
> > -
> > -				if ((attempts % 5) == 0) {
> > -					delay(1); /* Don't just spin the CPU */
> > -#ifdef DEBUG
> > -					xfs_rm_lock_delays++;
> > -#endif
> > -				}
> > -				goto again;
> > -			}
> > -		} else {
> > -			xfs_ilock(ip, XFS_ILOCK_EXCL);
> > -		}
> > -	} else if (e_inum < dp->i_ino) {
> > -		xfs_iunlock(dp, XFS_ILOCK_EXCL);
> > -
> > -		ips[0] = ip;
> > -		ips[1] = dp;
> > -		xfs_lock_inodes(ips, 2, XFS_ILOCK_EXCL);
> > -	}
> > -	/* else	 e_inum == dp->i_ino */
> > -	/*     This can happen if we're asked to lock /x/..
> > -	 *     the entry is "..", which is also the parent directory.
> > -	 */
> > -
> > -	return 0;
> > -}
> > -
> > -#ifdef DEBUG
> >  int xfs_locked_n;
> >  int xfs_small_retries;
> >  int xfs_middle_retries;
> > @@ -2135,6 +2030,45 @@ again:
> >  #endif
> >  }
> >  
> > +void
> > +xfs_lock_two_inodes(
> > +	xfs_inode_t		*ip0,
> > +	xfs_inode_t		*ip1,
> > +	uint			lock_mode)
> > +{
> > +	xfs_inode_t		*temp;
> > +	int			attempts = 0;
> > +	xfs_log_item_t		*lp;
> > +
> > +	ASSERT(ip0->i_ino != ip1->i_ino);
> > +
> > +	if (ip0->i_ino > ip1->i_ino) {
> > +		temp = ip0;
> > +		ip0 = ip1;
> > +		ip1 = temp;
> > +	}
> > +
> > + again:
> > +	xfs_ilock(ip0, xfs_lock_inumorder(lock_mode, 0));
> > +
> > +	/*
> > +	 * If the first lock we have locked is in the AIL, we must TRY to get
> > +	 * the second lock. If we can't get it, we must release the first one
> > +	 * and try again.
> > +	 */
> > +	lp = (xfs_log_item_t *)ip0->i_itemp;
> > +	if (lp && (lp->li_flags & XFS_LI_IN_AIL)) {
> > +		if (!xfs_ilock_nowait(ip1, xfs_lock_inumorder(lock_mode, 1))) {
> > +			xfs_iunlock(ip0, lock_mode);
> > +			if ((++attempts % 5) == 0)
> > +				delay(1); /* Don't just spin the CPU */
> > +			goto again;
> > +		}
> > +	} else {
> > +		xfs_ilock(ip1, xfs_lock_inumorder(lock_mode, 1));
> > +	}
> > +}
> > +
> >  int
> >  xfs_remove(
> >  	xfs_inode_t             *dp,
> > @@ -2210,9 +2144,7 @@ xfs_remove(
> >  		goto out_trans_cancel;
> >  	}
> >  
> > -	error = xfs_lock_dir_and_entry(dp, ip);
> > -	if (error)
> > -		goto out_trans_cancel;
> > +	xfs_lock_two_inodes(dp, ip, XFS_ILOCK_EXCL);
> >  
> >  	/*
> >  	 * At this point, we've gotten both the directory and the entry
> > @@ -2239,9 +2171,6 @@ xfs_remove(
> >  		}
> >  	}
> >  
> > -	/*
> > -	 * Entry must exist since we did a lookup in xfs_lock_dir_and_entry.
> > -	 */
> >  	XFS_BMAP_INIT(&free_list, &first_block);
> >  	error = xfs_dir_removename(tp, dp, name, ip->i_ino,
> >  					&first_block, &free_list, resblks);
> > @@ -2347,7 +2276,6 @@ xfs_link(
> >  {
> >  	xfs_mount_t		*mp = tdp->i_mount;
> >  	xfs_trans_t		*tp;
> > -	xfs_inode_t		*ips[2];
> >  	int			error;
> >  	xfs_bmap_free_t         free_list;
> >  	xfs_fsblock_t           first_block;
> > @@ -2395,15 +2323,7 @@ xfs_link(
> >  		goto error_return;
> >  	}
> >  
> > -	if (sip->i_ino < tdp->i_ino) {
> > -		ips[0] = sip;
> > -		ips[1] = tdp;
> > -	} else {
> > -		ips[0] = tdp;
> > -		ips[1] = sip;
> > -	}
> > -
> > -	xfs_lock_inodes(ips, 2, XFS_ILOCK_EXCL);
> > +	xfs_lock_two_inodes(sip, tdp, XFS_ILOCK_EXCL);
> >  
> >  	/*
> >  	 * Increment vnode ref counts since xfs_trans_commit &
> > Index: linux-2.6-xfs/fs/xfs/xfs_dfrag.c
> > ===================================================================
> > --- linux-2.6-xfs.orig/fs/xfs/xfs_dfrag.c	2008-04-26 17:43:14.000000000 +0200
> > +++ linux-2.6-xfs/fs/xfs/xfs_dfrag.c	2008-05-02 08:30:30.000000000 +0200
> > @@ -128,7 +128,6 @@ xfs_swap_extents(
> >  	xfs_swapext_t	*sxp)
> >  {
> >  	xfs_mount_t	*mp;
> > -	xfs_inode_t	*ips[2];
> >  	xfs_trans_t	*tp;
> >  	xfs_bstat_t	*sbp = &sxp->sx_stat;
> >  	bhv_vnode_t	*vp, *tvp;
> > @@ -153,16 +152,7 @@ xfs_swap_extents(
> >  	vp = XFS_ITOV(ip);
> >  	tvp = XFS_ITOV(tip);
> >  
> > -	/* Lock in i_ino order */
> > -	if (ip->i_ino < tip->i_ino) {
> > -		ips[0] = ip;
> > -		ips[1] = tip;
> > -	} else {
> > -		ips[0] = tip;
> > -		ips[1] = ip;
> > -	}
> > -
> > -	xfs_lock_inodes(ips, 2, lock_flags);
> > +	xfs_lock_two_inodes(ip, tip, lock_flags);
> >  	locked = 1;
> >  
> >  	/* Verify that both files have the same format */
> > @@ -265,7 +255,7 @@ xfs_swap_extents(
> >  		locked = 0;
> >  		goto error0;
> >  	}
> > -	xfs_lock_inodes(ips, 2, XFS_ILOCK_EXCL);
> > +	xfs_lock_two_inodes(ip, tip, XFS_ILOCK_EXCL);
> >  
> >  	/*
> >  	 * Count the number of extended attribute blocks
> > Index: linux-2.6-xfs/fs/xfs/xfs_inode.h
> > ===================================================================
> > --- linux-2.6-xfs.orig/fs/xfs/xfs_inode.h	2008-05-01 22:56:57.000000000 +0200
> > +++ linux-2.6-xfs/fs/xfs/xfs_inode.h	2008-05-02 08:30:30.000000000 +0200
> > @@ -522,6 +522,7 @@ void		xfs_iflush_all(struct xfs_mount *)
> >  void		xfs_ichgtime(xfs_inode_t *, int);
> >  xfs_fsize_t	xfs_file_last_byte(xfs_inode_t *);
> >  void		xfs_lock_inodes(xfs_inode_t **, int, uint);
> > +void		xfs_lock_two_inodes(xfs_inode_t *, xfs_inode_t *, uint);
> >  
> >  void		xfs_synchronize_atime(xfs_inode_t *);
> >  void		xfs_mark_inode_dirty_sync(xfs_inode_t *);
> ---end quoted text---
---end quoted text---