On 5/9/18 4:31 AM, Jan Kara wrote: > On Thu 03-05-18 18:26:26, Jan Kara wrote: >> Syzbot has reported that it can hit a NULL pointer dereference in >> wb_workfn() due to wb->bdi->dev being NULL. This indicates that >> wb_workfn() was called for an already unregistered bdi which should not >> happen as wb_shutdown() called from bdi_unregister() should make sure >> all pending writeback works are completed before bdi is unregistered. >> Except that wb_workfn() itself can requeue the work with: >> >> mod_delayed_work(bdi_wq, &wb->dwork, 0); >> >> and if this happens while wb_shutdown() is waiting in: >> >> flush_delayed_work(&wb->dwork); >> >> the dwork can get executed after wb_shutdown() has finished and >> bdi_unregister() has cleared wb->bdi->dev. >> >> Make wb_workfn() use wakeup_wb() for requeueing the work which takes all >> the necessary precautions against racing with bdi unregistration. >> >> CC: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> >> CC: Tejun Heo <tj@xxxxxxxxxx> >> Fixes: 839a8e8660b6777e7fe4e80af1a048aebe2b5977 >> Reported-by: syzbot <syzbot+9873874c735f2892e7e9@xxxxxxxxxxxxxxxxxxxxxxxxx> >> Signed-off-by: Jan Kara <jack@xxxxxxx> >> --- >> fs/fs-writeback.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) > > Jens, can you please pick up this patch? Probably for the next merge window > (I don't see a reason to rush this at this point in release cycle). Thanks! Looks like I never replied that back, but I did pick it up, and it did in fact go out last week for this series. So we should be all good. I didn't see a need to postpone it, it's obviously correct and fixes a real issue. -- Jens Axboe
