linux/fs/fuse
Maxim Patlasov 4a4ac4eba1 fuse: postpone end_page_writeback() in fuse_writepage_locked()
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>
Cc: stable@vger.kernel.org
2013-09-03 13:41:57 +02:00
..
control.c fs: Limit sys_mount to only request filesystem modules. 2013-03-03 19:36:31 -08:00
cuse.c Merge branch 'akpm' (incoming from Andrew) 2013-05-07 20:49:51 -07:00
dev.c Merge branch 'akpm' (incoming from Andrew) 2013-05-07 20:49:51 -07:00
dir.c fuse: readdirplus: cleanup 2013-07-17 14:53:54 +02:00
file.c fuse: postpone end_page_writeback() in fuse_writepage_locked() 2013-09-03 13:41:57 +02:00
fuse_i.h fuse: add flag to turn on async direct IO 2013-05-01 14:37:21 +02:00
inode.c mm: use totalram_pages instead of num_physpages at runtime 2013-07-03 16:07:35 -07:00
Kconfig fuse: Move CUSE Kconfig entry from fs/Kconfig into fs/fuse/Kconfig 2013-01-17 13:08:45 +01:00
Makefile CUSE: implement CUSE - Character device in Userspace 2009-06-09 11:24:11 +02:00