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@xxxxxx>
> >
> > 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---
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