From: Will Deacon <will@kernel.org>
To: Xogium <contact@xogium.me>
Cc: linux-arm-kernel@lists.infradead.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, gregkh@linuxfoundation.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
linux@armlinux.org.uk
Subject: Re: [breakage] panic() does not halt arm64 systems under certain conditions
Date: Tue, 17 Sep 2019 11:45:19 +0100 [thread overview]
Message-ID: <20190917104518.ovg6ivadyst7h76o@willie-the-truck> (raw)
In-Reply-To: <BX1W47JXPMR8.58IYW53H6M5N@dragonstone>
Hi,
[Expanding CC list; original message is here:
https://lore.kernel.org/linux-arm-kernel/BX1W47JXPMR8.58IYW53H6M5N@dragonstone/]
On Mon, Sep 16, 2019 at 09:35:36PM -0400, Xogium wrote:
> On arm64 in some situations userspace will continue running even after a
> panic. This means any userspace watchdog daemon will continue pinging,
> that service managers will keep running and displaying messages in certain
> cases, and that it is possible to enter via ssh in the now unstable system
> and to do almost anything except reboot/power off and etc. If
> CONFIG_PREEMPT=n is set in the kernel's configuration, the issue is fixed.
> I have reproduced the very same behavior with linux 4.19, 5.2 and 5.3. On
> x86/x86_64 the issue does not seem to be present at all.
I've managed to reproduce this under both 32-bit and 64-bit ARM kernels.
The issue is that the infinite loop at the end of panic() can run with
preemption enabled (particularly when invoking by echoing 'c' to
/proc/sysrq-trigger), so we end up rescheduling user tasks. On x86, this
doesn't happen because smp_send_stop() disables the local APIC in
native_stop_other_cpus() and so interrupts are effectively masked while
spinning.
A straightforward fix is to disable preemption explicitly on the panic()
path (diff below), but I've expanded the cc list to see both what others
think, but also in case smp_send_stop() is supposed to have the side-effect
of disabling interrupt delivery for the local CPU.
Will
--->8
diff --git a/kernel/panic.c b/kernel/panic.c
index 057540b6eee9..02d0de31c42d 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -179,6 +179,7 @@ void panic(const char *fmt, ...)
* after setting panic_cpu) from invoking panic() again.
*/
local_irq_disable();
+ preempt_disable_notrace();
/*
* It's possible to come here directly from a panic-assertion and
next parent reply other threads:[~2019-09-17 10:45 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <BX1W47JXPMR8.58IYW53H6M5N@dragonstone>
2019-09-17 10:45 ` Will Deacon [this message]
2019-09-17 10:51 ` [breakage] panic() does not halt arm64 systems under certain conditions Russell King - ARM Linux admin
2019-09-17 11:05 ` Will Deacon
2019-09-20 4:25 ` Jookia
2019-09-30 13:53 ` Will Deacon
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