[syzbot] upstream boot error: WARNING in __context_tracking_enter

[Russell King - ARM Linux admin]

On Fri, Mar 19, 2021 at 10:54:48AM +0100, Dmitry Vyukov wrote:
> .On Fri, Mar 19, 2021 at 10:44 AM syzbot
> <syzbot+f09a12b2c77bfbbf51bd at 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+f09a12b2c77bfbbf51bd at 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.

-- 
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