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Date:   Fri, 19 Mar 2021 10:10:43 +0000
From:   Russell King - ARM Linux admin <linux@armlinux.org.uk>
To:     Dmitry Vyukov <dvyukov@google.com>
Cc:     syzbot <syzbot+f09a12b2c77bfbbf51bd@syzkaller.appspotmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [syzbot] upstream boot error: WARNING in __context_tracking_enter
Message-ID: <20210319101043.GU1463@shell.armlinux.org.uk>
References: <0000000000004f14c105bde08f75@google.com>
 <CACT4Y+bLkFSc8manYrCukj-_nzwVsV9y6xYWXmGyYFS-PoBRPQ@mail.gmail.com>
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Sender: Russell King - ARM Linux admin <linux@armlinux.org.uk>
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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@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@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.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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