Patch "fuse: postpone end_page_writeback() in fuse_writepage_locked()" has been added to the 3.0-stable tree

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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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