xfs: reclaim inodes under a write lock

Make the inode tree reclaim walk exclusive to avoid races with
concurrent sync walkers and lookups. This is a version of a patch
posted by Christoph Hellwig that avoids all the code duplication.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

3 files changed, 71 insertions, 87 deletions

diff --git a/fs/xfs/linux-2.6/xfs_sync.c b/fs/xfs/linux-2.6/xfs_sync.c
index 6fed97a8cd3e..e19d25555c3f 100644
--- a/fs/xfs/linux-2.6/xfs_sync.c
+++ b/fs/xfs/linux-2.6/xfs_sync.c
@@ -65,7 +65,6 @@ xfs_inode_ag_lookup(
          * as the tree is sparse and a gang lookup walks to find
          * the number of objects requested.
          */
-        read_lock(&pag->pag_ici_lock);
         if (tag == XFS_ICI_NO_TAG) {
                 nr_found = radix_tree_gang_lookup(&pag->pag_ici_root,
                                 (void **)&ip, *first_index, 1);
@@ -74,7 +73,7 @@ xfs_inode_ag_lookup(
                                 (void **)&ip, *first_index, 1, tag);
         }
         if (!nr_found)
-                goto unlock;
+                return NULL;
 
         /*
          * Update the index for the next lookup. Catch overflows
@@ -84,13 +83,8 @@ xfs_inode_ag_lookup(
          */
         *first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
         if (*first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
-                goto unlock;
-
+                return NULL;
         return ip;
-
-unlock:
-        read_unlock(&pag->pag_ici_lock);
-        return NULL;
 }
 
 STATIC int
@@ -100,7 +94,8 @@ xfs_inode_ag_walk(
         int                     (*execute)(struct xfs_inode *ip,
                                            struct xfs_perag *pag, int flags),
         int                     flags,
-        int                     tag)
+        int                     tag,
+        int                     exclusive)
 {
         struct xfs_perag        *pag = &mp->m_perag[ag];
         uint32_t                first_index;
@@ -114,10 +109,20 @@ restart:
                 int             error = 0;
                 xfs_inode_t     *ip;
 
+                if (exclusive)
+                        write_lock(&pag->pag_ici_lock);
+                else
+                        read_lock(&pag->pag_ici_lock);
                 ip = xfs_inode_ag_lookup(mp, pag, &first_index, tag);
-                if (!ip)
+                if (!ip) {
+                        if (exclusive)
+                                write_unlock(&pag->pag_ici_lock);
+                        else
+                                read_unlock(&pag->pag_ici_lock);
                         break;
+                }
 
+                /* execute releases pag->pag_ici_lock */
                 error = execute(ip, pag, flags);
                 if (error == EAGAIN) {
                         skipped++;
@@ -125,9 +130,8 @@ restart:
                 }
                 if (error)
                         last_error = error;
-                /*
-                 * bail out if the filesystem is corrupted.
-                 */
+
+                /* bail out if the filesystem is corrupted.  */
                 if (error == EFSCORRUPTED)
                         break;
 
@@ -148,7 +152,8 @@ xfs_inode_ag_iterator(
         int                     (*execute)(struct xfs_inode *ip,
                                            struct xfs_perag *pag, int flags),
         int                     flags,
-        int                     tag)
+        int                     tag,
+        int                     exclusive)
 {
         int                     error = 0;
         int                     last_error = 0;
@@ -157,7 +162,8 @@ xfs_inode_ag_iterator(
         for (ag = 0; ag < mp->m_sb.sb_agcount; ag++) {
                 if (!mp->m_perag[ag].pag_ici_init)
                         continue;
-                error = xfs_inode_ag_walk(mp, ag, execute, flags, tag);
+                error = xfs_inode_ag_walk(mp, ag, execute, flags, tag,
+                                                exclusive);
                 if (error) {
                         last_error = error;
                         if (error == EFSCORRUPTED)
@@ -181,11 +187,7 @@ xfs_sync_inode_valid(
                 return EFSCORRUPTED;
         }
 
-        /*
-         * If we can't get a reference on the inode, it must be in reclaim.
-         * Leave it for the reclaim code to flush. Also avoid inodes that
-         * haven't been fully initialised.
-         */
+        /* If we can't get a reference on the inode, it must be in reclaim. */
         if (!igrab(inode)) {
                 read_unlock(&pag->pag_ici_lock);
                 return ENOENT;
@@ -282,7 +284,7 @@ xfs_sync_data(
         ASSERT((flags & ~(SYNC_TRYLOCK|SYNC_WAIT)) == 0);
 
         error = xfs_inode_ag_iterator(mp, xfs_sync_inode_data, flags,
-                                      XFS_ICI_NO_TAG);
+                                      XFS_ICI_NO_TAG, 0);
         if (error)
                 return XFS_ERROR(error);
 
@@ -304,7 +306,7 @@ xfs_sync_attr(
         ASSERT((flags & ~SYNC_WAIT) == 0);
 
         return xfs_inode_ag_iterator(mp, xfs_sync_inode_attr, flags,
-                                     XFS_ICI_NO_TAG);
+                                     XFS_ICI_NO_TAG, 0);
 }
 
 STATIC int
@@ -664,60 +666,6 @@ xfs_syncd_stop(
         kthread_stop(mp->m_sync_task);
 }
 
-STATIC int
-xfs_reclaim_inode(
-        xfs_inode_t     *ip,
-        int             sync_mode)
-{
-        xfs_perag_t     *pag = xfs_get_perag(ip->i_mount, ip->i_ino);
-
-        /* The hash lock here protects a thread in xfs_iget_core from
-         * racing with us on linking the inode back with a vnode.
-         * Once we have the XFS_IRECLAIM flag set it will not touch
-         * us.
-         */
-        write_lock(&pag->pag_ici_lock);
-        spin_lock(&ip->i_flags_lock);
-        if (__xfs_iflags_test(ip, XFS_IRECLAIM) ||
-            !__xfs_iflags_test(ip, XFS_IRECLAIMABLE)) {
-                spin_unlock(&ip->i_flags_lock);
-                write_unlock(&pag->pag_ici_lock);
-                return -EAGAIN;
-        }
-        __xfs_iflags_set(ip, XFS_IRECLAIM);
-        spin_unlock(&ip->i_flags_lock);
-        write_unlock(&pag->pag_ici_lock);
-        xfs_put_perag(ip->i_mount, pag);
-
-        /*
-         * If the inode is still dirty, then flush it out.  If the inode
-         * is not in the AIL, then it will be OK to flush it delwri as
-         * long as xfs_iflush() does not keep any references to the inode.
-         * We leave that decision up to xfs_iflush() since it has the
-         * knowledge of whether it's OK to simply do a delwri flush of
-         * the inode or whether we need to wait until the inode is
-         * pulled from the AIL.
-         * We get the flush lock regardless, though, just to make sure
-         * we don't free it while it is being flushed.
-         */
-        xfs_ilock(ip, XFS_ILOCK_EXCL);
-        xfs_iflock(ip);
-
-        /*
-         * In the case of a forced shutdown we rely on xfs_iflush() to
-         * wait for the inode to be unpinned before returning an error.
-         */
-        if (!is_bad_inode(VFS_I(ip)) && xfs_iflush(ip, sync_mode) == 0) {
-                /* synchronize with xfs_iflush_done */
-                xfs_iflock(ip);
-                xfs_ifunlock(ip);
-        }
-
-        xfs_iunlock(ip, XFS_ILOCK_EXCL);
-        xfs_ireclaim(ip);
-        return 0;
-}
-
 void
 __xfs_inode_set_reclaim_tag(
         struct xfs_perag        *pag,
@@ -760,19 +708,55 @@ __xfs_inode_clear_reclaim_tag(
 }
 
 STATIC int
-xfs_reclaim_inode_now(
+xfs_reclaim_inode(
         struct xfs_inode        *ip,
         struct xfs_perag        *pag,
-        int                     flags)
+        int                     sync_mode)
 {
-        /* ignore if already under reclaim */
-        if (xfs_iflags_test(ip, XFS_IRECLAIM)) {
-                read_unlock(&pag->pag_ici_lock);
+        /*
+         * The radix tree lock here protects a thread in xfs_iget from racing
+         * with us starting reclaim on the inode.  Once we have the
+         * XFS_IRECLAIM flag set it will not touch us.
+         */
+        spin_lock(&ip->i_flags_lock);
+        ASSERT_ALWAYS(__xfs_iflags_test(ip, XFS_IRECLAIMABLE));
+        if (__xfs_iflags_test(ip, XFS_IRECLAIM)) {
+                /* ignore as it is already under reclaim */
+                spin_unlock(&ip->i_flags_lock);
+                write_unlock(&pag->pag_ici_lock);
                 return 0;
         }
-        read_unlock(&pag->pag_ici_lock);
+        __xfs_iflags_set(ip, XFS_IRECLAIM);
+        spin_unlock(&ip->i_flags_lock);
+        write_unlock(&pag->pag_ici_lock);
+
+        /*
+         * If the inode is still dirty, then flush it out.  If the inode
+         * is not in the AIL, then it will be OK to flush it delwri as
+         * long as xfs_iflush() does not keep any references to the inode.
+         * We leave that decision up to xfs_iflush() since it has the
+         * knowledge of whether it's OK to simply do a delwri flush of
+         * the inode or whether we need to wait until the inode is
+         * pulled from the AIL.
+         * We get the flush lock regardless, though, just to make sure
+         * we don't free it while it is being flushed.
+         */
+        xfs_ilock(ip, XFS_ILOCK_EXCL);
+        xfs_iflock(ip);
 
-        return xfs_reclaim_inode(ip, flags);
+        /*
+         * In the case of a forced shutdown we rely on xfs_iflush() to
+         * wait for the inode to be unpinned before returning an error.
+         */
+        if (!is_bad_inode(VFS_I(ip)) && xfs_iflush(ip, sync_mode) == 0) {
+                /* synchronize with xfs_iflush_done */
+                xfs_iflock(ip);
+                xfs_ifunlock(ip);
+        }
+
+        xfs_iunlock(ip, XFS_ILOCK_EXCL);
+        xfs_ireclaim(ip);
+        return 0;
 }
 
 int
@@ -780,6 +764,6 @@ xfs_reclaim_inodes(
         xfs_mount_t     *mp,
         int             mode)
 {
-        return xfs_inode_ag_iterator(mp, xfs_reclaim_inode_now, mode,
-                                        XFS_ICI_RECLAIM_TAG);
+        return xfs_inode_ag_iterator(mp, xfs_reclaim_inode, mode,
+                                        XFS_ICI_RECLAIM_TAG, 1);
 }
diff --git a/fs/xfs/linux-2.6/xfs_sync.h b/fs/xfs/linux-2.6/xfs_sync.h
index a500b4d91835..ea932b43335d 100644
--- a/fs/xfs/linux-2.6/xfs_sync.h
+++ b/fs/xfs/linux-2.6/xfs_sync.h
@@ -54,6 +54,6 @@ void __xfs_inode_clear_reclaim_tag(struct xfs_mount *mp, struct xfs_perag *pag,
 int xfs_sync_inode_valid(struct xfs_inode *ip, struct xfs_perag *pag);
 int xfs_inode_ag_iterator(struct xfs_mount *mp,
         int (*execute)(struct xfs_inode *ip, struct xfs_perag *pag, int flags),
-        int flags, int tag);
+        int flags, int tag, int write_lock);
 
 #endif
diff --git a/fs/xfs/quota/xfs_qm_syscalls.c b/fs/xfs/quota/xfs_qm_syscalls.c
index 71af76fe8a23..873e07e29074 100644
--- a/fs/xfs/quota/xfs_qm_syscalls.c
+++ b/fs/xfs/quota/xfs_qm_syscalls.c
@@ -891,7 +891,7 @@ xfs_qm_dqrele_all_inodes(
         uint             flags)
 {
         ASSERT(mp->m_quotainfo);
-        xfs_inode_ag_iterator(mp, xfs_dqrele_inode, flags, XFS_ICI_NO_TAG);
+        xfs_inode_ag_iterator(mp, xfs_dqrele_inode, flags, XFS_ICI_NO_TAG, 0);
 }
 
 /*------------------------------------------------------------------------*/