fuse: get rid of ff->readdir.lock

The same protection is provided by file->f_pos_lock.

Note, this relies on the fact that file->f_mode has FMODE_ATOMIC_POS.
This flag is cleared by stream_open(), which would prevent locking of
f_pos_lock.

Prior to commit 7de64d52 ("fuse: break up fuse_open_common()")
FOPEN_STREAM on a directory would cause stream_open() to be called.
After this commit this is not done anymore, so f_pos_lock will always
be locked.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -69,7 +69,6 @@ struct fuse_file *fuse_file_alloc(struct fuse_mount *fm, bool release)
 	}
 
 	INIT_LIST_HEAD(&ff->write_entry);
-	mutex_init(&ff->readdir.lock);
 	refcount_set(&ff->count, 1);
 	RB_CLEAR_NODE(&ff->polled_node);
 	init_waitqueue_head(&ff->poll_wait);
@@ -82,7 +81,6 @@ struct fuse_file *fuse_file_alloc(struct fuse_mount *fm, bool release)
 void fuse_file_free(struct fuse_file *ff)
 {
 	kfree(ff->args);
-	mutex_destroy(&ff->readdir.lock);
 	kfree(ff);
 }
 

fs/fuse/fuse_i.h

@@ -243,12 +243,6 @@ struct fuse_file {
 
 	/* Readdir related */
 	struct {
-		/*
-		 * Protects below fields against (crazy) parallel readdir on
-		 * same open file.  Uncontended in the normal case.
-		 */
-		struct mutex lock;
-
 		/* Dir stream position */
 		loff_t pos;
 

fs/fuse/readdir.c

@@ -592,15 +592,11 @@ int fuse_readdir(struct file *file, struct dir_context *ctx)
 	if (fuse_is_bad(inode))
 		return -EIO;
 
-	mutex_lock(&ff->readdir.lock);
-
 	err = UNCACHED;
 	if (ff->open_flags & FOPEN_CACHE_DIR)
 		err = fuse_readdir_cached(file, ctx);
 	if (err == UNCACHED)
 		err = fuse_readdir_uncached(file, ctx);
 
-	mutex_unlock(&ff->readdir.lock);
-
 	return err;
 }