The locking in xfs_iget_cache_hit currently has numerous problems:
- we clear the reclaim tag without i_flags_lock which protects modifications
to it
- we call inode_init_always which can sleep with pag_ici_lock held
- we acquire and drop i_flags_lock a lot and thus provide no consistency
between the various flags we set/clear under it
This patch fixes all that with a major revamp of the locking in the function.
The new version acquires i_flags_lock early and only drops it once we need to
call into inode_init_always or before calling xfs_ilock.
This patch fixes a bug seen in the wild where we race modifying the reclaim tag.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: linux-2.6/fs/xfs/xfs_iget.c
===================================================================
--- linux-2.6.orig/fs/xfs/xfs_iget.c 2009-08-01 23:20:54.775080254 +0200
+++ linux-2.6/fs/xfs/xfs_iget.c 2009-08-01 23:20:54.807080483 +0200
@@ -133,80 +133,90 @@ xfs_iget_cache_hit(
int flags,
int lock_flags) __releases(pag->pag_ici_lock)
{
+ struct inode *inode = VFS_I(ip);
struct xfs_mount *mp = ip->i_mount;
- int error = EAGAIN;
+ int error;
+
+ spin_lock(&ip->i_flags_lock);
/*
- * If INEW is set this inode is being set up
- * If IRECLAIM is set this inode is being torn down
- * Pause and try again.
+ * This inode is being torn down, pause and try again.
*/
- if (xfs_iflags_test(ip, (XFS_INEW|XFS_IRECLAIM))) {
+ if (ip->i_flags & XFS_IRECLAIM) {
XFS_STATS_INC(xs_ig_frecycle);
+ error = EAGAIN;
goto out_error;
}
- /* If IRECLAIMABLE is set, we've torn down the vfs inode part */
- if (xfs_iflags_test(ip, XFS_IRECLAIMABLE)) {
+ /*
+ * If we are racing with another cache hit that is currently recycling
+ * this inode out of the XFS_IRECLAIMABLE state, wait for the
+ * initialisation to complete before continuing.
+ */
+ if (ip->i_flags & XFS_INEW) {
+ spin_unlock(&ip->i_flags_lock);
+ read_unlock(&pag->pag_ici_lock);
- /*
- * If lookup is racing with unlink, then we should return an
- * error immediately so we don't remove it from the reclaim
- * list and potentially leak the inode.
- */
- if ((ip->i_d.di_mode == 0) && !(flags & XFS_IGET_CREATE)) {
- error = ENOENT;
- goto out_error;
- }
+ XFS_STATS_INC(xs_ig_frecycle);
+ wait_on_inode(inode);
+ return EAGAIN;
+ }
+ /*
+ * If lookup is racing with unlink, then we should return an
+ * error immediately so we don't remove it from the reclaim
+ * list and potentially leak the inode.
+ */
+ if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
+ error = ENOENT;
+ goto out_error;
+ }
+
+ /*
+ * If IRECLAIMABLE is set, we've torn down the VFS inode already.
+ * Need to carefully get it back into useable state.
+ */
+ if (ip->i_flags & XFS_IRECLAIMABLE) {
xfs_itrace_exit_tag(ip, "xfs_iget.alloc");
/*
- * We need to re-initialise the VFS inode as it has been
- * 'freed' by the VFS. Do this here so we can deal with
- * errors cleanly, then tag it so it can be set up correctly
- * later.
+ * We need to set XFS_INEW atomically with clearing the
+ * reclaimable tag so that we do have an indicator of the
+ * inode still being initialized.
*/
- if (!inode_init_always(mp->m_super, VFS_I(ip))) {
+ ip->i_flags |= XFS_INEW;
+ __xfs_inode_clear_reclaim_tag(pag, ip);
+
+ spin_unlock(&ip->i_flags_lock);
+ read_unlock(&pag->pag_ici_lock);
+
+ if (unlikely(!inode_init_always(mp->m_super, inode))) {
+ /*
+ * Re-initializing the inode failed, and we are in deep
+ * trouble. Try to re-add it to the reclaim list.
+ */
+ read_lock(&pag->pag_ici_lock);
+ spin_lock(&ip->i_flags_lock);
+
+ ip->i_flags &= ~XFS_INEW;
+ __xfs_inode_set_reclaim_tag(pag, ip);
+
error = ENOMEM;
goto out_error;
}
-
- /*
- * We must set the XFS_INEW flag before clearing the
- * XFS_IRECLAIMABLE flag so that if a racing lookup does
- * not find the XFS_IRECLAIMABLE above but has the igrab()
- * below succeed we can safely check XFS_INEW to detect
- * that this inode is still being initialised.
- */
- xfs_iflags_set(ip, XFS_INEW);
- xfs_iflags_clear(ip, XFS_IRECLAIMABLE);
-
- /* clear the radix tree reclaim flag as well. */
- __xfs_inode_clear_reclaim_tag(mp, pag, ip);
- } else if (!igrab(VFS_I(ip))) {
+ inode->i_state = I_LOCK|I_NEW;
+ } else {
/* If the VFS inode is being torn down, pause and try again. */
- XFS_STATS_INC(xs_ig_frecycle);
- goto out_error;
- } else if (xfs_iflags_test(ip, XFS_INEW)) {
- /*
- * We are racing with another cache hit that is
- * currently recycling this inode out of the XFS_IRECLAIMABLE
- * state. Wait for the initialisation to complete before
- * continuing.
- */
- wait_on_inode(VFS_I(ip));
- }
+ if (!igrab(inode)) {
+ error = EAGAIN;
+ goto out_error;
+ }
- if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
- error = ENOENT;
- iput(VFS_I(ip));
- goto out_error;
+ /* We've got a live one. */
+ spin_unlock(&ip->i_flags_lock);
+ read_unlock(&pag->pag_ici_lock);
}
- /* We've got a live one. */
- read_unlock(&pag->pag_ici_lock);
-
if (lock_flags != 0)
xfs_ilock(ip, lock_flags);
@@ -216,6 +226,7 @@ xfs_iget_cache_hit(
return 0;
out_error:
+ spin_unlock(&ip->i_flags_lock);
read_unlock(&pag->pag_ici_lock);
return error;
}
Index: linux-2.6/fs/xfs/linux-2.6/xfs_sync.c
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_sync.c 2009-08-01 23:20:31.441330970 +0200
+++ linux-2.6/fs/xfs/linux-2.6/xfs_sync.c 2009-08-01 23:20:54.807080483 +0200
@@ -708,6 +708,17 @@ xfs_reclaim_inode(
return 0;
}
+void
+__xfs_inode_set_reclaim_tag(
+ struct xfs_perag *pag,
+ struct xfs_inode *ip)
+{
+ radix_tree_tag_set(&pag->pag_ici_root,
+ XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
+ XFS_ICI_RECLAIM_TAG);
+ ip->i_flags |= XFS_IRECLAIMABLE;
+}
+
/*
* We set the inode flag atomically with the radix tree tag.
* Once we get tag lookups on the radix tree, this inode flag
@@ -722,9 +733,7 @@ xfs_inode_set_reclaim_tag(
read_lock(&pag->pag_ici_lock);
spin_lock(&ip->i_flags_lock);
- radix_tree_tag_set(&pag->pag_ici_root,
- XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
- __xfs_iflags_set(ip, XFS_IRECLAIMABLE);
+ __xfs_inode_set_reclaim_tag(pag, ip);
spin_unlock(&ip->i_flags_lock);
read_unlock(&pag->pag_ici_lock);
xfs_put_perag(mp, pag);
@@ -732,27 +741,13 @@ xfs_inode_set_reclaim_tag(
void
__xfs_inode_clear_reclaim_tag(
- xfs_mount_t *mp,
- xfs_perag_t *pag,
- xfs_inode_t *ip)
+ struct xfs_perag *pag,
+ struct xfs_inode *ip)
{
+ ip->i_flags &= ~XFS_IRECLAIMABLE;
radix_tree_tag_clear(&pag->pag_ici_root,
- XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
-}
-
-void
-xfs_inode_clear_reclaim_tag(
- xfs_inode_t *ip)
-{
- xfs_mount_t *mp = ip->i_mount;
- xfs_perag_t *pag = xfs_get_perag(mp, ip->i_ino);
-
- read_lock(&pag->pag_ici_lock);
- spin_lock(&ip->i_flags_lock);
- __xfs_inode_clear_reclaim_tag(mp, pag, ip);
- spin_unlock(&ip->i_flags_lock);
- read_unlock(&pag->pag_ici_lock);
- xfs_put_perag(mp, pag);
+ XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
+ XFS_ICI_RECLAIM_TAG);
}
STATIC int
Index: linux-2.6/fs/xfs/linux-2.6/xfs_sync.h
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_sync.h 2009-08-01 23:20:31.449329683 +0200
+++ linux-2.6/fs/xfs/linux-2.6/xfs_sync.h 2009-08-01 23:20:54.808079772 +0200
@@ -48,9 +48,8 @@ int xfs_reclaim_inode(struct xfs_inode *
int xfs_reclaim_inodes(struct xfs_mount *mp, int mode);
void xfs_inode_set_reclaim_tag(struct xfs_inode *ip);
-void xfs_inode_clear_reclaim_tag(struct xfs_inode *ip);
-void __xfs_inode_clear_reclaim_tag(struct xfs_mount *mp, struct xfs_perag *pag,
- struct xfs_inode *ip);
+void __xfs_inode_set_reclaim_tag(struct xfs_perag *pag, struct xfs_inode *ip);
+void __xfs_inode_clear_reclaim_tag(struct xfs_perag *pag, struct xfs_inode *ip);
int xfs_sync_inode_valid(struct xfs_inode *ip, struct xfs_perag *pag);
int xfs_inode_ag_iterator(struct xfs_mount *mp,
--
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