[PATCH 075/104] fuse: postpone end_page_writeback() in fuse_writepage_locked()
luis.henriques at canonical.com
Mon Sep 30 10:10:52 UTC 2013
220.127.116.11 -stable review patch. If anyone has any objections, please let me know.
From: Maxim Patlasov <MPatlasov at 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
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
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 at parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi at suse.cz>
Signed-off-by: Luis Henriques <luis.henriques at 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 514f12a..e7785e4 100644
@@ -1296,7 +1296,6 @@ static int fuse_writepage_locked(struct page *page)
@@ -1304,6 +1303,8 @@ static int fuse_writepage_locked(struct page *page)
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