On Fri, May 29, 2020 at 4:05 PM Paul E. McKenney <[email protected]> wrote: > > On Fri, May 29, 2020 at 08:20:12AM +0200, Dmitry Vyukov wrote: > > On Thu, May 28, 2020 at 10:48 PM Paul E. McKenney <[email protected]> > > wrote: > > > > > > On Thu, May 28, 2020 at 10:19:02PM +0200, Thomas Gleixner wrote: > > > > Paul, > > > > > > > > "Paul E. McKenney" <[email protected]> writes: > > > > > On Thu, May 28, 2020 at 03:33:44PM +0200, Thomas Gleixner wrote: > > > > >> syzbot <[email protected]> > > > > >> writes: > > > > >> Weird. I have no idea how that thing is an EQS here. > > > > > > > > > > No argument on the "Weird" part! ;-) > > > > > > > > > > Is this a NO_HZ_FULL=y kernel? > > > > > > > > No, it has only NO_HZ_IDLE. > > > > > > > > https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10 > > > > > > OK, from the .config, another suggestion is to build the kernel > > > with CONFIG_RCU_EQS_DEBUG=y. This still requires that this issue be > > > reproduced, but it might catch the problem earlier. > > > > How much does it slow down execution? If we enable it on syzbot, it > > will affect all fuzzing done by syzbot always. > > It can tolerate significant slowdown and it's far from a production > > kernel (it enables KASAN, KCOV, LOCKDEP and more). But I am still > > asking because some debugging features are built without performance > > in mind at all (like let's just drop a global lock in every > > kmalloc/free, which may be too much even for a standard debug build). > > It is an extra WARN_ON_ONCE() with a simple comparison, but on almost > every kernel entry/exit path. > > So not something you want in production, but much lighter weight than > any of the tools you listed above. > > Full disclosure: It usually fires for new architectures or for new > timer hardware/drivers. Which might allow you to enable it selectively.
This sounds reasonable. I've enabled it: https://github.com/google/syzkaller/commit/3905eaae004605f4ec4dab83e6883173796118c8 syzbot will pick up within a day or so. Then crashes will have any additional checks captured. The arch/hardware is quite old: x86_64/GCE. It also booted for me in qemu without warnings. > Thanx, Paul > > > > > > If so, one possibility is that the call > > > > > to rcu_user_exit() went missing somehow. If not, then RCU should have > > > > > been watching userspace execution. > > > > > > > > > > Again, the only thing I can think of (should this prove to be > > > > > reproducible) is the rcu_dyntick trace event. > > > > > > > > :) > > > > > > > > Thanks, > > > > > > > > tglx > > > > > > Thanx, Paul > > > > > > -- > > > You received this message because you are subscribed to the Google Groups > > > "syzkaller-bugs" group. > > > To unsubscribe from this group and stop receiving emails from it, send an > > > email to [email protected]. > > > To view this discussion on the web visit > > > https://groups.google.com/d/msgid/syzkaller-bugs/20200528204839.GR2869%40paulmck-ThinkPad-P72. > > -- > You received this message because you are subscribed to the Google Groups > "syzkaller-bugs" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/syzkaller-bugs/20200529140521.GA2869%40paulmck-ThinkPad-P72.
