[XFS] Really fix use after free in xfs_iunpin.

The previous attempts to fix the linux inode use-after-free in xfs_iunpin
simply made the problem harder to hit. We actually need complete exclusion
between xfs_reclaim and xfs_iunpin, as well as ensuring that the i_flags
are consistent during both of these functions. Introduce a new spinlock
for exclusion and the i_flags, and fix up xfs_iunpin to use igrab before
marking the inode dirty.

SGI-PV: 952967
SGI-Modid: xfs-linux-melb:xfs-kern:26964a

Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

fs/xfs/linux-2.6/xfs_super.c

@@ -227,7 +227,9 @@ xfs_initialize_vnode(
 		xfs_revalidate_inode(XFS_BHVTOM(bdp), vp, ip);
 		xfs_set_inodeops(inode);
 
+		spin_lock(&ip->i_flags_lock);
 		ip->i_flags &= ~XFS_INEW;
+		spin_unlock(&ip->i_flags_lock);
 		barrier();
 
 		unlock_new_inode(inode);

fs/xfs/xfs_iget.c

@@ -243,7 +243,9 @@ again:
 
 				XFS_STATS_INC(xs_ig_found);
 
+				spin_lock(&ip->i_flags_lock);
 				ip->i_flags &= ~XFS_IRECLAIMABLE;
+				spin_unlock(&ip->i_flags_lock);
 				version = ih->ih_version;
 				read_unlock(&ih->ih_lock);
 				xfs_ihash_promote(ih, ip, version);
@@ -297,7 +299,9 @@ finish_inode:
 			if (lock_flags != 0)
 				xfs_ilock(ip, lock_flags);
 
+			spin_lock(&ip->i_flags_lock);
 			ip->i_flags &= ~XFS_ISTALE;
+			spin_unlock(&ip->i_flags_lock);
 
 			vn_trace_exit(vp, "xfs_iget.found",
 						(inst_t *)__return_address);
@@ -367,7 +371,9 @@ finish_inode:
 	ih->ih_next = ip;
 	ip->i_udquot = ip->i_gdquot = NULL;
 	ih->ih_version++;
+	spin_lock(&ip->i_flags_lock);
 	ip->i_flags |= XFS_INEW;
+	spin_unlock(&ip->i_flags_lock);
 
 	write_unlock(&ih->ih_lock);
 

fs/xfs/xfs_inode.c

@@ -867,6 +867,7 @@ xfs_iread(
 	ip = kmem_zone_zalloc(xfs_inode_zone, KM_SLEEP);
 	ip->i_ino = ino;
 	ip->i_mount = mp;
+	spin_lock_init(&ip->i_flags_lock);
 
 	/*
 	 * Get pointer's to the on-disk inode and the buffer containing it.
@@ -2214,7 +2215,9 @@ xfs_ifree_cluster(
 
 			if (ip == free_ip) {
 				if (xfs_iflock_nowait(ip)) {
+					spin_lock(&ip->i_flags_lock);
 					ip->i_flags |= XFS_ISTALE;
+					spin_unlock(&ip->i_flags_lock);
 
 					if (xfs_inode_clean(ip)) {
 						xfs_ifunlock(ip);
@@ -2228,7 +2231,9 @@ xfs_ifree_cluster(
 
 			if (xfs_ilock_nowait(ip, XFS_ILOCK_EXCL)) {
 				if (xfs_iflock_nowait(ip)) {
+					spin_lock(&ip->i_flags_lock);
 					ip->i_flags |= XFS_ISTALE;
+					spin_unlock(&ip->i_flags_lock);
 
 					if (xfs_inode_clean(ip)) {
 						xfs_ifunlock(ip);
@@ -2258,7 +2263,9 @@ xfs_ifree_cluster(
 				AIL_LOCK(mp,s);
 				iip->ili_flush_lsn = iip->ili_item.li_lsn;
 				AIL_UNLOCK(mp, s);
+				spin_lock(&iip->ili_inode->i_flags_lock);
 				iip->ili_inode->i_flags |= XFS_ISTALE;
+				spin_unlock(&iip->ili_inode->i_flags_lock);
 				pre_flushed++;
 			}
 			lip = lip->li_bio_list;
@@ -2754,19 +2761,29 @@ xfs_iunpin(
 		 * call as the inode reclaim may be blocked waiting for
 		 * the inode to become unpinned.
 		 */
+		struct inode *inode = NULL;
+
+		spin_lock(&ip->i_flags_lock);
 		if (!(ip->i_flags & (XFS_IRECLAIM|XFS_IRECLAIMABLE))) {
 			bhv_vnode_t	*vp = XFS_ITOV_NULL(ip);
 
 			/* make sync come back and flush this inode */
 			if (vp) {
-				struct inode	*inode = vn_to_inode(vp);
+				inode = vn_to_inode(vp);
 
 				if (!(inode->i_state &
-						(I_NEW|I_FREEING|I_CLEAR)))
-					mark_inode_dirty_sync(inode);
+						(I_NEW|I_FREEING|I_CLEAR))) {
+					inode = igrab(inode);
+					if (inode)
+						mark_inode_dirty_sync(inode);
+				} else
+					inode = NULL;
 			}
 		}
+		spin_unlock(&ip->i_flags_lock);
 		wake_up(&ip->i_ipin_wait);
+		if (inode)
+			iput(inode);
 	}
 }
 

fs/xfs/xfs_inode.h

@@ -267,6 +267,7 @@ typedef struct xfs_inode {
 	sema_t			i_flock;	/* inode flush lock */
 	atomic_t		i_pincount;	/* inode pin count */
 	wait_queue_head_t	i_ipin_wait;	/* inode pinning wait queue */
+	spinlock_t		i_flags_lock;	/* inode i_flags lock */
 #ifdef HAVE_REFCACHE
 	struct xfs_inode	**i_refcache;	/* ptr to entry in ref cache */
 	struct xfs_inode	*i_release;	/* inode to unref */

fs/xfs/xfs_itable.c

@@ -577,6 +577,7 @@ xfs_bulkstat(
 								      KM_SLEEP);
 						ip->i_ino = ino;
 						ip->i_mount = mp;
+						spin_lock_init(&ip->i_flags_lock);
 						if (bp)
 							xfs_buf_relse(bp);
 						error = xfs_itobp(mp, NULL, ip,

fs/xfs/xfs_vnodeops.c

@@ -3844,7 +3844,9 @@ xfs_reclaim(
 		XFS_MOUNT_ILOCK(mp);
 		vn_bhv_remove(VN_BHV_HEAD(vp), XFS_ITOBHV(ip));
 		list_add_tail(&ip->i_reclaim, &mp->m_del_inodes);
+		spin_lock(&ip->i_flags_lock);
 		ip->i_flags |= XFS_IRECLAIMABLE;
+		spin_unlock(&ip->i_flags_lock);
 		XFS_MOUNT_IUNLOCK(mp);
 	}
 	return 0;
@@ -3869,8 +3871,10 @@ xfs_finish_reclaim(
 	 * us.
 	 */
 	write_lock(&ih->ih_lock);
+	spin_lock(&ip->i_flags_lock);
 	if ((ip->i_flags & XFS_IRECLAIM) ||
 	    (!(ip->i_flags & XFS_IRECLAIMABLE) && vp == NULL)) {
+		spin_unlock(&ip->i_flags_lock);
 		write_unlock(&ih->ih_lock);
 		if (locked) {
 			xfs_ifunlock(ip);
@@ -3879,6 +3883,7 @@ xfs_finish_reclaim(
 		return 1;
 	}
 	ip->i_flags |= XFS_IRECLAIM;
+	spin_unlock(&ip->i_flags_lock);
 	write_unlock(&ih->ih_lock);
 
 	/*