On Wed, Feb 27, 2019 at 10:58:50AM +0100, Dmitry Vyukov wrote: > Peter, Ingo, do you have any updates on the > perf_event_open/sched_setattr stalls? This bug cause assorted hangs > throughout kernel and so is nasty. > > syzkaller tries to remove all syscalls from reproducers one-by-one. > Somehow without sched_setattr the hang did not reproduce (a bunch of > repros have perf_event_open+sched_setattr so somehow they seem to be > related) FWIW, at least for me, the repro.c with sched_setattr commented out (see the repro.c attached to a message[1] earlier in the thread) it was reproducing reliably on a 2 CPU, 2 GB memory KVM using the ext4.git tree (dev branch, 5.0-rc3 plus ext4 commits for the next merge window) using a Debian stable-based VM[2]. [1] https://groups.google.com/d/msg/syzkaller-bugs/ByPpM3WZw1s/li7SsaEyAgAJ [2] https://mirrors.edge.kernel.org/pub/linux/kernel/people/tytso/kvm-xfstests/root_fs.img.amd64 > But even with perfect repros machines still won't be > able to tell in all cases that even though the hang happened in ext4 > code, the root cause is actually another scheduler-related system > call. So thanks for looking into this. To be clear, there was *not* a scheduler-related system call in the repro.c I was playing with (see [2]); just perf_event_open(2) and sendfile(2). Cheers, - Ted
