lkml.org 
[lkml]   [2013]   [Sep]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 60/93] fuse: postpone end_page_writeback() in fuse_writepage_locked()
Date
3.8.13.10 -stable review patch.  If anyone has any objections, please let me know.

------------------

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: Kamal Mostafa <kamal@canonical.com>
---
fs/fuse/file.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f3ab824..e9c40f3 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1299,7 +1299,6 @@ static int fuse_writepage_locked(struct page *page)

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);
@@ -1307,6 +1306,8 @@ static int fuse_writepage_locked(struct page *page)
fuse_flush_writepages(inode);
spin_unlock(&fc->lock);

+ end_page_writeback(page);
+
return 0;

err_free:
--
1.8.1.2


\
 
 \ /
  Last update: 2013-09-20 22:41    [W:0.240 / U:36.928 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site