ocfs2: Fix deadlock on umount

In commit ea455f8a, we moved the dentry lock
put process into ocfs2_wq. This causes problems during umount because ocfs2_wq
can drop references to inodes while they are being invalidated by
invalidate_inodes() causing all sorts of nasty things (invalidate_inodes()
ending in an infinite loop, "Busy inodes after umount" messages etc.).

We fix the problem by stopping ocfs2_wq from doing any further releasing of
inode references on the superblock being unmounted, wait until it finishes
the current round of releasing and finally cleaning up all the references in
dentry_lock_list from ocfs2_put_super().

The issue was tracked down by Tao Ma <tao.ma@oracle.com>.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Joel Becker <joel.becker@oracle.com>

fs/ocfs2/dcache.c

@@ -310,22 +310,19 @@ out_attach:
 	return ret;
 }
 
-static DEFINE_SPINLOCK(dentry_list_lock);
+DEFINE_SPINLOCK(dentry_list_lock);
 
 /* We limit the number of dentry locks to drop in one go. We have
  * this limit so that we don't starve other users of ocfs2_wq. */
 #define DL_INODE_DROP_COUNT 64
 
 /* Drop inode references from dentry locks */
-void ocfs2_drop_dl_inodes(struct work_struct *work)
+static void __ocfs2_drop_dl_inodes(struct ocfs2_super *osb, int drop_count)
 {
-	struct ocfs2_super *osb = container_of(work, struct ocfs2_super,
-					       dentry_lock_work);
 	struct ocfs2_dentry_lock *dl;
-	int drop_count = DL_INODE_DROP_COUNT;
 
 	spin_lock(&dentry_list_lock);
-	while (osb->dentry_lock_list && drop_count--) {
+	while (osb->dentry_lock_list && (drop_count < 0 || drop_count--)) {
 		dl = osb->dentry_lock_list;
 		osb->dentry_lock_list = dl->dl_next;
 		spin_unlock(&dentry_list_lock);
@@ -333,11 +330,32 @@ void ocfs2_drop_dl_inodes(struct work_struct *work)
 		kfree(dl);
 		spin_lock(&dentry_list_lock);
 	}
-	if (osb->dentry_lock_list)
+	spin_unlock(&dentry_list_lock);
+}
+
+void ocfs2_drop_dl_inodes(struct work_struct *work)
+{
+	struct ocfs2_super *osb = container_of(work, struct ocfs2_super,
+					       dentry_lock_work);
+
+	__ocfs2_drop_dl_inodes(osb, DL_INODE_DROP_COUNT);
+	/*
+	 * Don't queue dropping if umount is in progress. We flush the
+	 * list in ocfs2_dismount_volume
+	 */
+	spin_lock(&dentry_list_lock);
+	if (osb->dentry_lock_list &&
+	    !ocfs2_test_osb_flag(osb, OCFS2_OSB_DROP_DENTRY_LOCK_IMMED))
 		queue_work(ocfs2_wq, &osb->dentry_lock_work);
 	spin_unlock(&dentry_list_lock);
 }
 
+/* Flush the whole work queue */
+void ocfs2_drop_all_dl_inodes(struct ocfs2_super *osb)
+{
+	__ocfs2_drop_dl_inodes(osb, -1);
+}
+
 /*
  * ocfs2_dentry_iput() and friends.
  *
@@ -368,7 +386,8 @@ static void ocfs2_drop_dentry_lock(struct ocfs2_super *osb,
 	/* We leave dropping of inode reference to ocfs2_wq as that can
 	 * possibly lead to inode deletion which gets tricky */
 	spin_lock(&dentry_list_lock);
-	if (!osb->dentry_lock_list)
+	if (!osb->dentry_lock_list &&
+	    !ocfs2_test_osb_flag(osb, OCFS2_OSB_DROP_DENTRY_LOCK_IMMED))
 		queue_work(ocfs2_wq, &osb->dentry_lock_work);
 	dl->dl_next = osb->dentry_lock_list;
 	osb->dentry_lock_list = dl;

fs/ocfs2/dcache.h

@@ -49,10 +49,13 @@ struct ocfs2_dentry_lock {
 int ocfs2_dentry_attach_lock(struct dentry *dentry, struct inode *inode,
 			     u64 parent_blkno);
 
+extern spinlock_t dentry_list_lock;
+
 void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
 			   struct ocfs2_dentry_lock *dl);
 
 void ocfs2_drop_dl_inodes(struct work_struct *work);
+void ocfs2_drop_all_dl_inodes(struct ocfs2_super *osb);
 
 struct dentry *ocfs2_find_local_alias(struct inode *inode, u64 parent_blkno,
 				      int skip_unhashed);

fs/ocfs2/ocfs2.h

@@ -224,10 +224,12 @@ enum ocfs2_mount_options
 	OCFS2_MOUNT_GRPQUOTA = 1 << 10, /* We support group quotas */
 };
 
-#define OCFS2_OSB_SOFT_RO	0x0001
-#define OCFS2_OSB_HARD_RO	0x0002
-#define OCFS2_OSB_ERROR_FS	0x0004
-#define OCFS2_DEFAULT_ATIME_QUANTUM	60
+#define OCFS2_OSB_SOFT_RO			0x0001
+#define OCFS2_OSB_HARD_RO			0x0002
+#define OCFS2_OSB_ERROR_FS			0x0004
+#define OCFS2_OSB_DROP_DENTRY_LOCK_IMMED	0x0008
+
+#define OCFS2_DEFAULT_ATIME_QUANTUM		60
 
 struct ocfs2_journal;
 struct ocfs2_slot_info;
@@ -490,6 +492,18 @@ static inline void ocfs2_set_osb_flag(struct ocfs2_super *osb,
 	spin_unlock(&osb->osb_lock);
 }
 
+
+static inline unsigned long  ocfs2_test_osb_flag(struct ocfs2_super *osb,
+						 unsigned long flag)
+{
+	unsigned long ret;
+
+	spin_lock(&osb->osb_lock);
+	ret = osb->osb_flags & flag;
+	spin_unlock(&osb->osb_lock);
+	return ret;
+}
+
 static inline void ocfs2_set_ro_flag(struct ocfs2_super *osb,
 				     int hard)
 {

fs/ocfs2/super.c

@@ -1213,14 +1213,27 @@ static int ocfs2_get_sb(struct file_system_type *fs_type,
 			   mnt);
 }
 
+static void ocfs2_kill_sb(struct super_block *sb)
+{
+	struct ocfs2_super *osb = OCFS2_SB(sb);
+
+	/* Prevent further queueing of inode drop events */
+	spin_lock(&dentry_list_lock);
+	ocfs2_set_osb_flag(osb, OCFS2_OSB_DROP_DENTRY_LOCK_IMMED);
+	spin_unlock(&dentry_list_lock);
+	/* Wait for work to finish and/or remove it */
+	cancel_work_sync(&osb->dentry_lock_work);
+
+	kill_block_super(sb);
+}
+
 static struct file_system_type ocfs2_fs_type = {
 	.owner          = THIS_MODULE,
 	.name           = "ocfs2",
 	.get_sb         = ocfs2_get_sb, /* is this called when we mount
 					* the fs? */
-	.kill_sb        = kill_block_super, /* set to the generic one
-					     * right now, but do we
-					     * need to change that? */
+	.kill_sb        = ocfs2_kill_sb,
+
 	.fs_flags       = FS_REQUIRES_DEV|FS_RENAME_DOES_D_MOVE,
 	.next           = NULL
 };
@@ -1819,6 +1832,12 @@ static void ocfs2_dismount_volume(struct super_block *sb, int mnt_err)
 
 	debugfs_remove(osb->osb_ctxt);
 
+	/*
+	 * Flush inode dropping work queue so that deletes are
+	 * performed while the filesystem is still working
+	 */
+	ocfs2_drop_all_dl_inodes(osb);
+
 	/* Orphan scan should be stopped as early as possible */
 	ocfs2_orphan_scan_stop(osb);