This is a note to let you know that I've just added the patch titled
fuse: postpone end_page_writeback() in fuse_writepage_locked()
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fuse-postpone-end_page_writeback-in-fuse_writepage_locked.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4a4ac4eba1010ef9a804569058ab29e3450c0315 Mon Sep 17 00:00:00 2001
From: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx>
Date: Mon, 12 Aug 2013 20:39:30 +0400
Subject: fuse: postpone end_page_writeback() in fuse_writepage_locked()
From: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/fuse/file.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1298,7 +1298,6 @@ 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);
@@ -1306,6 +1305,8 @@ static int fuse_writepage_locked(struct
fuse_flush_writepages(inode);
spin_unlock(&fc->lock);
+ end_page_writeback(page);
+
return 0;
err_free:
Patches currently in stable-queue which might be from MPatlasov@xxxxxxxxxxxxx are
queue-3.0/fuse-postpone-end_page_writeback-in-fuse_writepage_locked.patch
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