On Thu, Feb 18, 2016 at 05:09:48PM +0100, Jan Kara wrote: > On Thu 07-01-16 17:55:21, Jan Kara wrote: > > From: Jan Kara <jack@xxxxxxxx> > > > > 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. > > > > CC: stable@xxxxxxxxxxxxxxx > > Reported-by: Nikolay Borisov <kernel@xxxxxxxx> > > Signed-off-by: Jan Kara <jack@xxxxxxx> > > Ping Ted? This seems to have fallen through the cracks? Oops, sorry. Thanks, applied. - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
