smb: During unmount, ensure all cached dir instances drop their dentry

The unmount process (cifs_kill_sb() calling close_all_cached_dirs()) can
race with various cached directory operations, which ultimately results
in dentries not being dropped and these kernel BUGs:

BUG: Dentry ffff88814f37e358{i=1000000000080,n=/}  still in use (2) [unmount of cifs cifs]
VFS: Busy inodes after unmount of cifs (cifs)
------------[ cut here ]------------
kernel BUG at fs/super.c:661!

This happens when a cfid is in the process of being cleaned up when, and
has been removed from the cfids->entries list, including:

- Receiving a lease break from the server
- Server reconnection triggers invalidate_all_cached_dirs(), which
  removes all the cfids from the list
- The laundromat thread decides to expire an old cfid.

To solve these problems, dropping the dentry is done in queued work done
in a newly-added cfid_put_wq workqueue, and close_all_cached_dirs()
flushes that workqueue after it drops all the dentries of which it's
aware. This is a global workqueue (rather than scoped to a mount), but
the queued work is minimal.

The final cleanup work for cleaning up a cfid is performed via work
queued in the serverclose_wq workqueue; this is done separate from
dropping the dentries so that close_all_cached_dirs() doesn't block on
any server operations.

Both of these queued works expect to invoked with a cfid reference and
a tcon reference to avoid those objects from being freed while the work
is ongoing.

While we're here, add proper locking to close_all_cached_dirs(), and
locking around the freeing of cfid->dentry.

Fixes: ebe98f1447 ("cifs: enable caching of directories for which a lease is held")
Cc: stable@vger.kernel.org
Signed-off-by: Paul Aurich <paul@darkrain42.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/cached_dir.c

@@ -17,6 +17,11 @@ static void free_cached_dir(struct cached_fid *cfid);
 static void smb2_close_cached_fid(struct kref *ref);
 static void cfids_laundromat_worker(struct work_struct *work);
 
+struct cached_dir_dentry {
+	struct list_head entry;
+	struct dentry *dentry;
+};
+
 static struct cached_fid *find_or_create_cached_dir(struct cached_fids *cfids,
 						    const char *path,
 						    bool lookup_only,
@@ -472,7 +477,10 @@ void close_all_cached_dirs(struct cifs_sb_info *cifs_sb)
 	struct cifs_tcon *tcon;
 	struct tcon_link *tlink;
 	struct cached_fids *cfids;
+	struct cached_dir_dentry *tmp_list, *q;
+	LIST_HEAD(entry);
 
+	spin_lock(&cifs_sb->tlink_tree_lock);
 	for (node = rb_first(root); node; node = rb_next(node)) {
 		tlink = rb_entry(node, struct tcon_link, tl_rbnode);
 		tcon = tlink_tcon(tlink);
@@ -481,11 +489,30 @@ void close_all_cached_dirs(struct cifs_sb_info *cifs_sb)
 		cfids = tcon->cfids;
 		if (cfids == NULL)
 			continue;
+		spin_lock(&cfids->cfid_list_lock);
 		list_for_each_entry(cfid, &cfids->entries, entry) {
-			dput(cfid->dentry);
+			tmp_list = kmalloc(sizeof(*tmp_list), GFP_ATOMIC);
+			if (tmp_list == NULL)
+				break;
+			spin_lock(&cfid->fid_lock);
+			tmp_list->dentry = cfid->dentry;
 			cfid->dentry = NULL;
+			spin_unlock(&cfid->fid_lock);
+
+			list_add_tail(&tmp_list->entry, &entry);
 		}
+		spin_unlock(&cfids->cfid_list_lock);
 	}
+	spin_unlock(&cifs_sb->tlink_tree_lock);
+
+	list_for_each_entry_safe(tmp_list, q, &entry, entry) {
+		list_del(&tmp_list->entry);
+		dput(tmp_list->dentry);
+		kfree(tmp_list);
+	}
+
+	/* Flush any pending work that will drop dentries */
+	flush_workqueue(cfid_put_wq);
 }
 
 /*
@@ -496,14 +523,18 @@ void invalidate_all_cached_dirs(struct cifs_tcon *tcon)
 {
 	struct cached_fids *cfids = tcon->cfids;
 	struct cached_fid *cfid, *q;
-	LIST_HEAD(entry);
 
 	if (cfids == NULL)
 		return;
 
+	/*
+	 * Mark all the cfids as closed, and move them to the cfids->dying list.
+	 * They'll be cleaned up later by cfids_invalidation_worker. Take
+	 * a reference to each cfid during this process.
+	 */
 	spin_lock(&cfids->cfid_list_lock);
 	list_for_each_entry_safe(cfid, q, &cfids->entries, entry) {
-		list_move(&cfid->entry, &entry);
+		list_move(&cfid->entry, &cfids->dying);
 		cfids->num_entries--;
 		cfid->is_open = false;
 		cfid->on_list = false;
@@ -516,26 +547,47 @@ void invalidate_all_cached_dirs(struct cifs_tcon *tcon)
 		} else
 			kref_get(&cfid->refcount);
 	}
+	/*
+	 * Queue dropping of the dentries once locks have been dropped
+	 */
+	if (!list_empty(&cfids->dying))
+		queue_work(cfid_put_wq, &cfids->invalidation_work);
 	spin_unlock(&cfids->cfid_list_lock);
-
-	list_for_each_entry_safe(cfid, q, &entry, entry) {
-		list_del(&cfid->entry);
-		cancel_work_sync(&cfid->lease_break);
-		/*
-		 * Drop the ref-count from above, either the lease-ref (if there
-		 * was one) or the extra one acquired.
-		 */
-		kref_put(&cfid->refcount, smb2_close_cached_fid);
-	}
 }
 
 static void
-smb2_cached_lease_break(struct work_struct *work)
+cached_dir_offload_close(struct work_struct *work)
 {
 	struct cached_fid *cfid = container_of(work,
-				struct cached_fid, lease_break);
+				struct cached_fid, close_work);
+	struct cifs_tcon *tcon = cfid->tcon;
+
+	WARN_ON(cfid->on_list);
 
 	kref_put(&cfid->refcount, smb2_close_cached_fid);
+	cifs_put_tcon(tcon, netfs_trace_tcon_ref_put_cached_close);
+}
+
+/*
+ * Release the cached directory's dentry, and then queue work to drop cached
+ * directory itself (closing on server if needed).
+ *
+ * Must be called with a reference to the cached_fid and a reference to the
+ * tcon.
+ */
+static void cached_dir_put_work(struct work_struct *work)
+{
+	struct cached_fid *cfid = container_of(work, struct cached_fid,
+					       put_work);
+	struct dentry *dentry;
+
+	spin_lock(&cfid->fid_lock);
+	dentry = cfid->dentry;
+	cfid->dentry = NULL;
+	spin_unlock(&cfid->fid_lock);
+
+	dput(dentry);
+	queue_work(serverclose_wq, &cfid->close_work);
 }
 
 int cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16])
@@ -562,8 +614,10 @@ int cached_dir_lease_break(struct cifs_tcon *tcon, __u8 lease_key[16])
 			cfid->on_list = false;
 			cfids->num_entries--;
 
-			queue_work(cifsiod_wq,
-				   &cfid->lease_break);
+			++tcon->tc_count;
+			trace_smb3_tcon_ref(tcon->debug_id, tcon->tc_count,
+					    netfs_trace_tcon_ref_get_cached_lease_break);
+			queue_work(cfid_put_wq, &cfid->put_work);
 			spin_unlock(&cfids->cfid_list_lock);
 			return true;
 		}
@@ -585,7 +639,8 @@ static struct cached_fid *init_cached_dir(const char *path)
 		return NULL;
 	}
 
-	INIT_WORK(&cfid->lease_break, smb2_cached_lease_break);
+	INIT_WORK(&cfid->close_work, cached_dir_offload_close);
+	INIT_WORK(&cfid->put_work, cached_dir_put_work);
 	INIT_LIST_HEAD(&cfid->entry);
 	INIT_LIST_HEAD(&cfid->dirents.entries);
 	mutex_init(&cfid->dirents.de_mutex);
@@ -598,6 +653,9 @@ static void free_cached_dir(struct cached_fid *cfid)
 {
 	struct cached_dirent *dirent, *q;
 
+	WARN_ON(work_pending(&cfid->close_work));
+	WARN_ON(work_pending(&cfid->put_work));
+
 	dput(cfid->dentry);
 	cfid->dentry = NULL;
 
@@ -615,10 +673,30 @@ static void free_cached_dir(struct cached_fid *cfid)
 	kfree(cfid);
 }
 
+static void cfids_invalidation_worker(struct work_struct *work)
+{
+	struct cached_fids *cfids = container_of(work, struct cached_fids,
+						 invalidation_work);
+	struct cached_fid *cfid, *q;
+	LIST_HEAD(entry);
+
+	spin_lock(&cfids->cfid_list_lock);
+	/* move cfids->dying to the local list */
+	list_cut_before(&entry, &cfids->dying, &cfids->dying);
+	spin_unlock(&cfids->cfid_list_lock);
+
+	list_for_each_entry_safe(cfid, q, &entry, entry) {
+		list_del(&cfid->entry);
+		/* Drop the ref-count acquired in invalidate_all_cached_dirs */
+		kref_put(&cfid->refcount, smb2_close_cached_fid);
+	}
+}
+
 static void cfids_laundromat_worker(struct work_struct *work)
 {
 	struct cached_fids *cfids;
 	struct cached_fid *cfid, *q;
+	struct dentry *dentry;
 	LIST_HEAD(entry);
 
 	cfids = container_of(work, struct cached_fids, laundromat_work.work);
@@ -644,18 +722,28 @@ static void cfids_laundromat_worker(struct work_struct *work)
 
 	list_for_each_entry_safe(cfid, q, &entry, entry) {
 		list_del(&cfid->entry);
-		/*
-		 * Cancel and wait for the work to finish in case we are racing
-		 * with it.
-		 */
-		cancel_work_sync(&cfid->lease_break);
-		/*
-		 * Drop the ref-count from above, either the lease-ref (if there
-		 * was one) or the extra one acquired.
-		 */
-		kref_put(&cfid->refcount, smb2_close_cached_fid);
+
+		spin_lock(&cfid->fid_lock);
+		dentry = cfid->dentry;
+		cfid->dentry = NULL;
+		spin_unlock(&cfid->fid_lock);
+
+		dput(dentry);
+		if (cfid->is_open) {
+			spin_lock(&cifs_tcp_ses_lock);
+			++cfid->tcon->tc_count;
+			trace_smb3_tcon_ref(cfid->tcon->debug_id, cfid->tcon->tc_count,
+					    netfs_trace_tcon_ref_get_cached_laundromat);
+			spin_unlock(&cifs_tcp_ses_lock);
+			queue_work(serverclose_wq, &cfid->close_work);
+		} else
+			/*
+			 * Drop the ref-count from above, either the lease-ref (if there
+			 * was one) or the extra one acquired.
+			 */
+			kref_put(&cfid->refcount, smb2_close_cached_fid);
 	}
-	queue_delayed_work(cifsiod_wq, &cfids->laundromat_work,
+	queue_delayed_work(cfid_put_wq, &cfids->laundromat_work,
 			   dir_cache_timeout * HZ);
 }
 
@@ -668,9 +756,11 @@ struct cached_fids *init_cached_dirs(void)
 		return NULL;
 	spin_lock_init(&cfids->cfid_list_lock);
 	INIT_LIST_HEAD(&cfids->entries);
+	INIT_LIST_HEAD(&cfids->dying);
 
+	INIT_WORK(&cfids->invalidation_work, cfids_invalidation_worker);
 	INIT_DELAYED_WORK(&cfids->laundromat_work, cfids_laundromat_worker);
-	queue_delayed_work(cifsiod_wq, &cfids->laundromat_work,
+	queue_delayed_work(cfid_put_wq, &cfids->laundromat_work,
 			   dir_cache_timeout * HZ);
 
 	return cfids;
@@ -689,6 +779,7 @@ void free_cached_dirs(struct cached_fids *cfids)
 		return;
 
 	cancel_delayed_work_sync(&cfids->laundromat_work);
+	cancel_work_sync(&cfids->invalidation_work);
 
 	spin_lock(&cfids->cfid_list_lock);
 	list_for_each_entry_safe(cfid, q, &cfids->entries, entry) {
@@ -696,6 +787,11 @@ void free_cached_dirs(struct cached_fids *cfids)
 		cfid->is_open = false;
 		list_move(&cfid->entry, &entry);
 	}
+	list_for_each_entry_safe(cfid, q, &cfids->dying, entry) {
+		cfid->on_list = false;
+		cfid->is_open = false;
+		list_move(&cfid->entry, &entry);
+	}
 	spin_unlock(&cfids->cfid_list_lock);
 
 	list_for_each_entry_safe(cfid, q, &entry, entry) {

fs/smb/client/cached_dir.h

@@ -44,7 +44,8 @@ struct cached_fid {
 	spinlock_t fid_lock;
 	struct cifs_tcon *tcon;
 	struct dentry *dentry;
-	struct work_struct lease_break;
+	struct work_struct put_work;
+	struct work_struct close_work;
 	struct smb2_file_all_info file_all_info;
 	struct cached_dirents dirents;
 };
@@ -53,10 +54,13 @@ struct cached_fid {
 struct cached_fids {
 	/* Must be held when:
 	 * - accessing the cfids->entries list
+	 * - accessing the cfids->dying list
 	 */
 	spinlock_t cfid_list_lock;
 	int num_entries;
 	struct list_head entries;
+	struct list_head dying;
+	struct work_struct invalidation_work;
 	struct delayed_work laundromat_work;
 };
 

fs/smb/client/cifsfs.c

@@ -157,6 +157,7 @@ struct workqueue_struct	*fileinfo_put_wq;
 struct workqueue_struct	*cifsoplockd_wq;
 struct workqueue_struct	*deferredclose_wq;
 struct workqueue_struct	*serverclose_wq;
+struct workqueue_struct	*cfid_put_wq;
 __u32 cifs_lock_secret;
 
 /*
@@ -1920,9 +1921,16 @@ init_cifs(void)
 		goto out_destroy_deferredclose_wq;
 	}
 
+	cfid_put_wq = alloc_workqueue("cfid_put_wq",
+				      WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
+	if (!cfid_put_wq) {
+		rc = -ENOMEM;
+		goto out_destroy_serverclose_wq;
+	}
+
 	rc = cifs_init_inodecache();
 	if (rc)
-		goto out_destroy_serverclose_wq;
+		goto out_destroy_cfid_put_wq;
 
 	rc = cifs_init_netfs();
 	if (rc)
@@ -1990,6 +1998,8 @@ out_destroy_netfs:
 	cifs_destroy_netfs();
 out_destroy_inodecache:
 	cifs_destroy_inodecache();
+out_destroy_cfid_put_wq:
+	destroy_workqueue(cfid_put_wq);
 out_destroy_serverclose_wq:
 	destroy_workqueue(serverclose_wq);
 out_destroy_deferredclose_wq:

fs/smb/client/cifsglob.h

@@ -1991,7 +1991,7 @@ require use of the stronger protocol */
  * cifsInodeInfo->lock_sem	cifsInodeInfo->llist		cifs_init_once
  *				->can_cache_brlcks
  * cifsInodeInfo->deferred_lock	cifsInodeInfo->deferred_closes	cifsInodeInfo_alloc
- * cached_fid->fid_mutex		cifs_tcon->crfid		tcon_info_alloc
+ * cached_fids->cfid_list_lock	cifs_tcon->cfids->entries	 init_cached_dirs
  * cifsFileInfo->fh_mutex		cifsFileInfo			cifs_new_fileinfo
  * cifsFileInfo->file_info_lock	cifsFileInfo->count		cifs_new_fileinfo
  *				->invalidHandle			initiate_cifs_search
@@ -2079,6 +2079,7 @@ extern struct workqueue_struct *fileinfo_put_wq;
 extern struct workqueue_struct *cifsoplockd_wq;
 extern struct workqueue_struct *deferredclose_wq;
 extern struct workqueue_struct *serverclose_wq;
+extern struct workqueue_struct *cfid_put_wq;
 extern __u32 cifs_lock_secret;
 
 extern mempool_t *cifs_sm_req_poolp;

fs/smb/client/inode.c

@@ -2496,13 +2496,10 @@ cifs_dentry_needs_reval(struct dentry *dentry)
 		return true;
 
 	if (!open_cached_dir_by_dentry(tcon, dentry->d_parent, &cfid)) {
-		spin_lock(&cfid->fid_lock);
 		if (cfid->time && cifs_i->time > cfid->time) {
-			spin_unlock(&cfid->fid_lock);
 			close_cached_dir(cfid);
 			return false;
 		}
-		spin_unlock(&cfid->fid_lock);
 		close_cached_dir(cfid);
 	}
 	/*

fs/smb/client/trace.h

@@ -44,6 +44,8 @@
 	EM(netfs_trace_tcon_ref_free_ipc,		"FRE Ipc   ") \
 	EM(netfs_trace_tcon_ref_free_ipc_fail,		"FRE Ipc-F ") \
 	EM(netfs_trace_tcon_ref_free_reconnect_server,	"FRE Reconn") \
+	EM(netfs_trace_tcon_ref_get_cached_laundromat,	"GET Ch-Lau") \
+	EM(netfs_trace_tcon_ref_get_cached_lease_break,	"GET Ch-Lea") \
 	EM(netfs_trace_tcon_ref_get_cancelled_close,	"GET Cn-Cls") \
 	EM(netfs_trace_tcon_ref_get_dfs_refer,		"GET DfsRef") \
 	EM(netfs_trace_tcon_ref_get_find,		"GET Find  ") \
@@ -52,6 +54,7 @@
 	EM(netfs_trace_tcon_ref_new,			"NEW       ") \
 	EM(netfs_trace_tcon_ref_new_ipc,		"NEW Ipc   ") \
 	EM(netfs_trace_tcon_ref_new_reconnect_server,	"NEW Reconn") \
+	EM(netfs_trace_tcon_ref_put_cached_close,	"PUT Ch-Cls") \
 	EM(netfs_trace_tcon_ref_put_cancelled_close,	"PUT Cn-Cls") \
 	EM(netfs_trace_tcon_ref_put_cancelled_close_fid, "PUT Cn-Fid") \
 	EM(netfs_trace_tcon_ref_put_cancelled_mid,	"PUT Cn-Mid") \