On Wed, Mar 20, 2019 at 01:58:06PM +0100, Jan Kara wrote: > Hello, > > commit 310ca162d77 "block/loop: Use global lock for ioctl() operation." has > been pushed to multiple stable trees. This patch is a part of larger series > that overhauls the locking inside loopback device upstream and for 4.4, > 4.9, and 4.14 stable trees only this patch from the series is applied. Our > testing now has shown [1] that the patch alone makes present deadlocks > inside loopback driver more likely (the openqa test in our infrastructure > didn't hit the deadlock before whereas with the new kernel it hits it > reliably every time). So I would suggest we revert 310ca162d77 from 4.4, > 4.9, and 4.14 kernels. Ugh, ok. > Another option would be to backport other locking fixes for the loop > device but honestly I don't think that's a stable material - never heard > of real users hitting problems, only syzkaller could, and we are still > fixing up some small glitches resulting from that rework... I tried to backport a number of the loop fixes, and odds are I am the one that grabbed this. There are other loop locking fixes in the stable releases, I don't know if I can just revert this one, let me check... And yes, I did get some loop bugreports from the Android kernel team as they are using loop devices in large numbers on the new Android release for something. So I think they have already backported a number of these fixes to their trees, which made me want to push these out to more people. Also, given that syzbot has a reproducer for 310ca162d77, are we worst off if we revert it? thanks, greg k-h
