| From 4a4ac4eba1010ef9a804569058ab29e3450c0315 Mon Sep 17 00:00:00 2001 |
| From: Maxim Patlasov <MPatlasov@parallels.com> |
| Date: Mon, 12 Aug 2013 20:39:30 +0400 |
| Subject: fuse: postpone end_page_writeback() in fuse_writepage_locked() |
| |
| From: Maxim Patlasov <MPatlasov@parallels.com> |
| |
| commit 4a4ac4eba1010ef9a804569058ab29e3450c0315 upstream. |
| |
| The patch fixes a race between ftruncate(2), mmap-ed write and write(2): |
| |
| 1) An user makes a page dirty via mmap-ed write. |
| 2) The user performs shrinking truncate(2) intended to purge the page. |
| 3) Before fuse_do_setattr calls truncate_pagecache, the page goes to |
| writeback. fuse_writepage_locked fills FUSE_WRITE request and releases |
| the original page by end_page_writeback. |
| 4) fuse_do_setattr() completes and successfully returns. Since now, i_mutex |
| is free. |
| 5) Ordinary write(2) extends i_size back to cover the page. Note that |
| fuse_send_write_pages do wait for fuse writeback, but for another |
| page->index. |
| 6) fuse_writepage_locked proceeds by queueing FUSE_WRITE request. |
| fuse_send_writepage is supposed to crop inarg->size of the request, |
| but it doesn't because i_size has already been extended back. |
| |
| Moving end_page_writeback to the end of fuse_writepage_locked fixes the |
| race because now the fact that truncate_pagecache is successfully returned |
| infers that fuse_writepage_locked has already called end_page_writeback. |
| And this, in turn, infers that fuse_flush_writepages has already called |
| fuse_send_writepage, and the latter used valid (shrunk) i_size. write(2) |
| could not extend it because of i_mutex held by ftruncate(2). |
| |
| Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com> |
| Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/fuse/file.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| --- a/fs/fuse/file.c |
| +++ b/fs/fuse/file.c |
| @@ -1530,7 +1530,6 @@ static int fuse_writepage_locked(struct |
| |
| inc_bdi_stat(mapping->backing_dev_info, BDI_WRITEBACK); |
| inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP); |
| - end_page_writeback(page); |
| |
| spin_lock(&fc->lock); |
| list_add(&req->writepages_entry, &fi->writepages); |
| @@ -1538,6 +1537,8 @@ static int fuse_writepage_locked(struct |
| fuse_flush_writepages(inode); |
| spin_unlock(&fc->lock); |
| |
| + end_page_writeback(page); |
| + |
| return 0; |
| |
| err_free: |
