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authorMaxim Patlasov <MPatlasov@parallels.com>2013-08-12 20:39:30 +0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-09-26 16:52:49 -0700
commitf35b12e6453f12bb65f7d492b751f05cdeb41518 (patch)
parentcd76cc4459ac83aa17226ceac9058abbfe8385c8 (diff)
fuse: postpone end_page_writeback() in fuse_writepage_locked()
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 2 insertions, 1 deletions
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 79fca8dfa3ea..2e1c10feed9a 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1298,7 +1298,6 @@ 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);
list_add(&req->writepages_entry, &fi->writepages);
@@ -1306,6 +1305,8 @@ static int fuse_writepage_locked(struct page *page)
+ end_page_writeback(page);
return 0;