On Tue, Oct 16, 2018 at 01:36:54PM +0200, Jan Kara wrote: > On Wed 10-10-18 14:28:09, Jan Kara wrote: > > On Wed 10-10-18 13:42:27, Johannes Thumshirn wrote: > > > On Wed, Oct 10, 2018 at 07:19:00PM +0900, Tetsuo Handa wrote: > > > > On 2018/10/10 19:04, Jan Kara wrote: > > > > > Hi, > > > > > > > > > > this patch series fixes oops and possible deadlocks as reported by > > > > > syzbot [1] > > > > > [2]. The second patch in the series (from Tetsuo) fixes the oops, the > > > > > remaining > > > > > patches are cleaning up the locking in the loop driver so that we can > > > > > in the > > > > > end reasonably easily switch to rereading partitions without holding > > > > > mutex > > > > > protecting the loop device. > > > > > > > > > > I have lightly tested the patches by creating, deleting, and > > > > > modifying loop > > > > > devices but if there's some more comprehensive loopback device > > > > > testsuite, I > > > > > can try running it. Review is welcome! > > > > > > > > Testing on linux-next by syzbot will be the most comprehensive. ;-) > > > > > > Apart from that blktests has a loop category and I think it could also be > > > worthwhile to add the C reproducer from syzkaller to blktests. > > > > Yeah, I did run loop tests now and they ran fine. I can try converting the > > syzbot reproducers into something legible but it will take a while. > > So I took a stab at this. But I hit two issues: > > 1) For the reproducer triggering the lockdep warning, you need a 32-bit > binary (so that it uses compat_ioctl). I don't think we want to introduce > 32-bit devel environment dependency to blktests. With 64-bits, the problem > is also there but someone noticed and silenced lockdep (with a reason that > I consider is incorrect)... I think the test is still worth it though as > I'll remove the lockdep-fooling code in my patches and thus new breakage > will be noticed.
Agreed, even if it doesn't trigger lockdep now, it's a good regression test. > 2) For the oops (use-after-free) issue I was not able to reproduce that in > my test KVM in couple hours. The race window is rather narrow and syzbot > with KASAN and everything hit it only 11 times. So I'm not sure how useful > that test is. Any opinions? I'd say we should add it anyways. If anything, it's a smoke test for changing fds on a loop device. You could add a note that the race it's testing for is very narrow.
