fuse: wait for writeback in fuse_file_fallocate()

The patch fixes a race between mmap-ed write and fallocate(PUNCH_HOLE):

1) An user makes a page dirty via mmap-ed write.
2) The user performs fallocate(2) with mode == PUNCH_HOLE|KEEP_SIZE
   and <offset, size> covering the page.
3) Before truncate_pagecache_range call from fuse_file_fallocate,
   the page goes to write-back. The page is fully processed by fuse_writepage
   (including end_page_writeback on the page), but fuse_flush_writepages did
   nothing because fi->writectr < 0.
4) truncate_pagecache_range is called and fuse_file_fallocate is finishing
   by calling fuse_release_nowrite. The latter triggers processing queued
   write-back request which will write stale data to the hole soon.

Changed in v2 (thanks to Brian for suggestion):
 - Do not truncate page cache until FUSE_FALLOCATE succeeded. Otherwise,
   we can end up in returning -ENOTSUPP while user data is already punched
   from page cache. Use filemap_write_and_wait_range() instead.
Changed in v3 (thanks to Miklos for suggestion):
 - fuse_wait_on_writeback() is prone to livelocks; use fuse_set_nowrite()
   instead. So far as we need a dirty-page barrier only, fuse_sync_writes()
   should be enough.
 - rebased to for-linus branch of fuse.git

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: stable@vger.kernel.org

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index d409deafc67b2f6c94fb3fa53b96a21c60585d56..f9f07c4fa517bd457c3c52b64a92ddae86db1c71 100644 (file)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2484,8 +2484,15 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
 
        if (lock_inode) {
                mutex_lock(&inode->i_mutex);
-               if (mode & FALLOC_FL_PUNCH_HOLE)
-                       fuse_set_nowrite(inode);
+               if (mode & FALLOC_FL_PUNCH_HOLE) {
+                       loff_t endbyte = offset + length - 1;
+                       err = filemap_write_and_wait_range(inode->i_mapping,
+                                                          offset, endbyte);
+                       if (err)
+                               goto out;
+
+                       fuse_sync_writes(inode);
+               }
        }
 
        req = fuse_get_req_nopages(fc);
@@ -2520,11 +2527,8 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
        fuse_invalidate_attr(inode);
 
 out:
-       if (lock_inode) {
-               if (mode & FALLOC_FL_PUNCH_HOLE)
-                       fuse_release_nowrite(inode);
+       if (lock_inode)
                mutex_unlock(&inode->i_mutex);
-       }
 
        return err;
 }