Commit 4a4ac4eba1010ef9a804569058ab29e3450c0315
Committed by
Miklos Szeredi
1 parent
6e4664525b
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
Showing 1 changed file with 2 additions and 1 deletions Side-by-side Diff
fs/fuse/file.c
... | ... | @@ -1529,13 +1529,14 @@ |
1529 | 1529 | |
1530 | 1530 | inc_bdi_stat(mapping->backing_dev_info, BDI_WRITEBACK); |
1531 | 1531 | inc_zone_page_state(tmp_page, NR_WRITEBACK_TEMP); |
1532 | - end_page_writeback(page); | |
1533 | 1532 | |
1534 | 1533 | spin_lock(&fc->lock); |
1535 | 1534 | list_add(&req->writepages_entry, &fi->writepages); |
1536 | 1535 | list_add_tail(&req->list, &fi->queued_writes); |
1537 | 1536 | fuse_flush_writepages(inode); |
1538 | 1537 | spin_unlock(&fc->lock); |
1538 | + | |
1539 | + end_page_writeback(page); | |
1539 | 1540 | |
1540 | 1541 | return 0; |
1541 | 1542 |