From 01dda5f90b3e0fd5e65b5d25d347b05fdf08bd27 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 19 Feb 2016 00:18:25 -0500 Subject: [PATCH] ext4: fix bh->b_state corruption commit ed8ad83808f009ade97ebbf6519bc3a97fefbc0c upstream. ext4 can update bh->b_state non-atomically in _ext4_get_block() and ext4_da_get_block_prep(). Usually this is fine since bh is just a temporary storage for mapping information on stack but in some cases it can be fully living bh attached to a page. In such case non-atomic update of bh->b_state can race with an atomic update which then gets lost. Usually when we are mapping bh and thus updating bh->b_state non-atomically, nobody else touches the bh and so things work out fine but there is one case to especially worry about: ext4_finish_bio() uses BH_Uptodate_Lock on the first bh in the page to synchronize handling of PageWriteback state. So when blocksize < pagesize, we can be atomically modifying bh->b_state of a buffer that actually isn't under IO and thus can race e.g. with delalloc trying to map that buffer. The result is that we can mistakenly set / clear BH_Uptodate_Lock bit resulting in the corruption of PageWriteback state or missed unlock of BH_Uptodate_Lock. Fix the problem by always updating bh->b_state bits atomically. Reported-by: Nikolay Borisov Signed-off-by: Jan Kara Signed-off-by: Theodore Ts'o [bwh: Backported to 3.2: - s/READ_ONCE/ACCESS_ONCE/ - Adjust context] Signed-off-by: Ben Hutchings --- Reading git-format-patch failed