fuse: serialize dirops by default

Negotiate with userspace filesystems whether they support parallel readdir
and lookup.  Disable parallelism by default for fear of breaking fuse
filesystems.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 9902af79c01a ("parallel lookups: actual switch to rwsem")
Fixes: d9b3dbdcfd62 ("fuse: switch to ->iterate_shared()")

3 files changed, 31 insertions, 1 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index ccd4971cc6c1..264f07c7754e 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -341,8 +341,10 @@ static struct dentry *fuse_lookup(struct inode *dir, struct dentry *entry,
         struct dentry *newent;
         bool outarg_valid = true;
 
+        fuse_lock_inode(dir);
         err = fuse_lookup_name(dir->i_sb, get_node_id(dir), &entry->d_name,
                                &outarg, &inode);
+        fuse_unlock_inode(dir);
         if (err == -ENOENT) {
                 outarg_valid = false;
                 err = 0;
@@ -1341,7 +1343,9 @@ static int fuse_readdir(struct file *file, struct dir_context *ctx)
                 fuse_read_fill(req, file, ctx->pos, PAGE_SIZE,
                                FUSE_READDIR);
         }
+        fuse_lock_inode(inode);
         fuse_request_send(fc, req);
+        fuse_unlock_inode(inode);
         nbytes = req->out.args[0].size;
         err = req->out.h.error;
         fuse_put_request(fc, req);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index eddbe02c4028..929c383432b0 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -110,6 +110,9 @@ struct fuse_inode {
 
         /** Miscellaneous bits describing inode state */
         unsigned long state;
+
+        /** Lock for serializing lookup and readdir for back compatibility*/
+        struct mutex mutex;
 };
 
 /** FUSE inode state bits */
@@ -540,6 +543,9 @@ struct fuse_conn {
         /** write-back cache policy (default is write-through) */
         unsigned writeback_cache:1;
 
+        /** allow parallel lookups and readdir (default is serialized) */
+        unsigned parallel_dirops:1;
+
         /*
          * The following bitfields are only for optimization purposes
          * and hence races in setting them will not cause malfunction
@@ -956,4 +962,7 @@ int fuse_do_setattr(struct inode *inode, struct iattr *attr,
 
 void fuse_set_initialized(struct fuse_conn *fc);
 
+void fuse_unlock_inode(struct inode *inode);
+void fuse_lock_inode(struct inode *inode);
+
 #endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 1ce67668a8e1..9961d8432ce3 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -97,6 +97,7 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
         INIT_LIST_HEAD(&fi->queued_writes);
         INIT_LIST_HEAD(&fi->writepages);
         init_waitqueue_head(&fi->page_waitq);
+        mutex_init(&fi->mutex);
         fi->forget = fuse_alloc_forget();
         if (!fi->forget) {
                 kmem_cache_free(fuse_inode_cachep, inode);
@@ -117,6 +118,7 @@ static void fuse_destroy_inode(struct inode *inode)
         struct fuse_inode *fi = get_fuse_inode(inode);
         BUG_ON(!list_empty(&fi->write_files));
         BUG_ON(!list_empty(&fi->queued_writes));
+        mutex_destroy(&fi->mutex);
         kfree(fi->forget);
         call_rcu(&inode->i_rcu, fuse_i_callback);
 }
@@ -351,6 +353,18 @@ int fuse_reverse_inval_inode(struct super_block *sb, u64 nodeid,
         return 0;
 }
 
+void fuse_lock_inode(struct inode *inode)
+{
+        if (!get_fuse_conn(inode)->parallel_dirops)
+                mutex_lock(&get_fuse_inode(inode)->mutex);
+}
+
+void fuse_unlock_inode(struct inode *inode)
+{
+        if (!get_fuse_conn(inode)->parallel_dirops)
+                mutex_unlock(&get_fuse_inode(inode)->mutex);
+}
+
 static void fuse_umount_begin(struct super_block *sb)
 {
         fuse_abort_conn(get_fuse_conn_super(sb));
@@ -898,6 +912,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
                                 fc->async_dio = 1;
                         if (arg->flags & FUSE_WRITEBACK_CACHE)
                                 fc->writeback_cache = 1;
+                        if (arg->flags & FUSE_PARALLEL_DIROPS)
+                                fc->parallel_dirops = 1;
                         if (arg->time_gran && arg->time_gran <= 1000000000)
                                 fc->sb->s_time_gran = arg->time_gran;
                 } else {
@@ -928,7 +944,8 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
                 FUSE_SPLICE_WRITE | FUSE_SPLICE_MOVE | FUSE_SPLICE_READ |
                 FUSE_FLOCK_LOCKS | FUSE_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
                 FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO |
-                FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT;
+                FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT |
+                FUSE_PARALLEL_DIROPS;
         req->in.h.opcode = FUSE_INIT;
         req->in.numargs = 1;
         req->in.args[0].size = sizeof(*arg);