On Mon, Mar 22, 2021 at 6:22 PM Mark Rutland <mark.rutl...@arm.com> wrote: > > Hi Russell, > > On Fri, Mar 19, 2021 at 10:10:43AM +0000, Russell King - ARM Linux admin > wrote: > > On Fri, Mar 19, 2021 at 10:54:48AM +0100, Dmitry Vyukov wrote: > > > .On Fri, Mar 19, 2021 at 10:44 AM syzbot > > > <syzbot+f09a12b2c77bfbbf5...@syzkaller.appspotmail.com> wrote: > > > > syzbot found the following issue on: > > > > > > > > HEAD commit: 8b12a62a Merge tag 'drm-fixes-2021-03-19' of > > > > git://anongit.. > > > > git tree: upstream > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17e815aed00000 > > > > kernel config: > > > > https://syzkaller.appspot.com/x/.config?x=cfeed364fc353c32 > > > > dashboard link: > > > > https://syzkaller.appspot.com/bug?extid=f09a12b2c77bfbbf51bd > > > > userspace arch: arm > > > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the > > > > commit: > > > > Reported-by: syzbot+f09a12b2c77bfbbf5...@syzkaller.appspotmail.com > > > > > > > > > +Mark, arm > > > It did not get far with CONFIG_CONTEXT_TRACKING_FORCE (kernel doesn't > > > boot). > > > > It seems that the path: > > > > context_tracking_user_enter() > > user_enter() > > context_tracking_enter() > > __context_tracking_enter() > > vtime_user_enter() > > > > expects preemption to be disabled. It effectively is, because local > > interrupts are disabled by context_tracking_enter(). > > > > However, the requirement for preemption to be disabled is not > > documented... so shrug. Maybe someone can say what the real requirements > > are here. > > From dealing with this recently on arm64, theis is a bit messy. To > handle this robustly we need to do a few things in sequence, including > using the *_irqoff() variants of the context_tracking_user_*() > functions. > > I wrote down the constraints in commit: > > 23529049c6842382 ("arm64: entry: fix non-NMI user<->kernel transitions") > > For user->kernel transitions, the arch code needs the following sequence > before invoking arbitrary kernel C code: > > lockdep_hardirqs_off(CALLER_ADDR0); > user_exit_irqoff(); > trace_hardirqs_off_finish(); > > For kernel->user transitions, the arch code needs the following sequence > once it will no longer invoke arbitrary kernel C code, just before > returning to userspace: > > trace_hardirqs_on_prepare(); > lockdep_hardirqs_on_prepare(CALLER_ADDR0); > user_enter_irqoff(); > lockdep_hardirqs_on(CALLER_ADDR0);
Hi Russell, Does Mark's comment make sense to you? lockdep_assert_preemption_disabled() also checks "&& this_cpu_read(hardirqs_enabled)", so is it that we also need hardirq's disabled around user_enter/exit? This issue currently prevents ARM boot on syzbot.
