[PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[Hoeun Ryu]

 Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
version in panic path) introduced crash_smp_send_stop() which is a weak
function and can be overriden by architecture codes to fix the side effect
caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
notifiers" option).

 ARM64 architecture uses the weak version function and the problem is that
the weak function simply calls smp_send_stop() which makes other CPUs
offline and takes away the chance to save crash information for nonpanic
CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
option is enabled.

 Calling smp_send_crash_stop() in the function is useless because all
nonpanic CPUs are already offline by smp_send_stop() in this case and
smp_send_crash_stop() only works against online CPUs.

 The result is that /proc/vmcore is not available with the error messages;
"Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".

 crash_smp_send_stop() is implemented for ARM64 architecture to fix this
problem and the function (strong symbol version) saves crash information
for nonpanic CPUs using smp_send_crash_stop() and machine_crash_shutdown()
tries to save crash information for nonpanic CPUs only when
crash_kexec_post_notifiers kernel option is disabled.

Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
---
 arch/arm64/kernel/machine_kexec.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index 481f54a..ec55cd8 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -213,6 +213,23 @@ void machine_kexec(struct kimage *kimage)
 	BUG(); /* Should never get here. */
 }
 
+void crash_smp_send_stop(void)
+{
+	static int cpus_stopped;
+
+	/*
+	 * This function can be called twice in panic path, but obviously
+	 * we execute this only once.
+	 */
+	if (cpus_stopped)
+		return;
+
+	/* shutdown non-crashing cpus */
+	smp_send_crash_stop();
+
+	cpus_stopped = 1;
+}
+
 static void machine_kexec_mask_interrupts(void)
 {
 	unsigned int i;
@@ -252,7 +269,7 @@ void machine_crash_shutdown(struct pt_regs *regs)
 	local_irq_disable();
 
 	/* shutdown non-crashing cpus */
-	smp_send_crash_stop();
+	crash_smp_send_stop();
 
 	/* for crashing cpu */
 	crash_save_cpu(regs, smp_processor_id());
-- 
2.7.4

[PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[James Morse]

Hi Hoeun,

On 04/08/17 08:02, Hoeun Ryu wrote:
>  Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
> version in panic path) introduced crash_smp_send_stop() which is a weak
> function and can be overriden by architecture codes to fix the side effect
> caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
> notifiers" option).

If I've understood correctly: if we boot with this option core code doesn't use
our machine_crash_shutdown(), and instead calls crash_smp_send_stop(), which we
don't have, so it uses the default smp_send_stop(), which doesn't save the regs.

Thanks for catching this!


Could we rename smp_send_crash_stop() crash_smp_send_stop() and add the
called-twice logic there? They are similar enough that I'm getting them muddled
already!


Thanks,

James


>  ARM64 architecture uses the weak version function and the problem is that
> the weak function simply calls smp_send_stop() which makes other CPUs
> offline and takes away the chance to save crash information for nonpanic
> CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
> option is enabled.
> 
>  Calling smp_send_crash_stop() in the function is useless because all
> nonpanic CPUs are already offline by smp_send_stop() in this case and
> smp_send_crash_stop() only works against online CPUs.
> 
>  The result is that /proc/vmcore is not available with the error messages;
> "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".
> 
>  crash_smp_send_stop() is implemented for ARM64 architecture to fix this
> problem and the function (strong symbol version) saves crash information
> for nonpanic CPUs using smp_send_crash_stop() and machine_crash_shutdown()
> tries to save crash information for nonpanic CPUs only when
> crash_kexec_post_notifiers kernel option is disabled.

[PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[AKASHI Takahiro]

On Fri, Aug 04, 2017 at 11:38:16AM +0100, James Morse wrote:
> Hi Hoeun,
> 
> On 04/08/17 08:02, Hoeun Ryu wrote:
> >  Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
> > version in panic path) introduced crash_smp_send_stop() which is a weak
> > function and can be overriden by architecture codes to fix the side effect
> > caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
> > notifiers" option).
> 
> If I've understood correctly: if we boot with this option core code doesn't use
> our machine_crash_shutdown(), and instead calls crash_smp_send_stop(), which we

No. Machine_crash_shutdown() is always called, but at that time,
all the cpus other than the crashing cpu have already died in this case.

> don't have, so it uses the default smp_send_stop(), which doesn't save the regs.
> 
> Thanks for catching this!
> 
> 
> Could we rename smp_send_crash_stop() crash_smp_send_stop() and add the
> called-twice logic there? They are similar enough that I'm getting them muddled
> already!
> 

Nice.

-Takahiro AKASHI

> 
> Thanks,
> 
> James
> 
> 
> >  ARM64 architecture uses the weak version function and the problem is that
> > the weak function simply calls smp_send_stop() which makes other CPUs
> > offline and takes away the chance to save crash information for nonpanic
> > CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
> > option is enabled.
> > 
> >  Calling smp_send_crash_stop() in the function is useless because all
> > nonpanic CPUs are already offline by smp_send_stop() in this case and
> > smp_send_crash_stop() only works against online CPUs.
> > 
> >  The result is that /proc/vmcore is not available with the error messages;
> > "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".
> > 
> >  crash_smp_send_stop() is implemented for ARM64 architecture to fix this
> > problem and the function (strong symbol version) saves crash information
> > for nonpanic CPUs using smp_send_crash_stop() and machine_crash_shutdown()
> > tries to save crash information for nonpanic CPUs only when
> > crash_kexec_post_notifiers kernel option is disabled.
> 
> 

[PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[Hoeun Ryu]

> On 4 Aug 2017, at 8:43 PM, AKASHI Takahiro <takahiro.akashi@linaro.org> wrote:
> 
>> On Fri, Aug 04, 2017 at 11:38:16AM +0100, James Morse wrote:
>> Hi Hoeun,
>> 
>>> On 04/08/17 08:02, Hoeun Ryu wrote:
>>> Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
>>> version in panic path) introduced crash_smp_send_stop() which is a weak
>>> function and can be overriden by architecture codes to fix the side effect
>>> caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
>>> notifiers" option).
>> 
>> If I've understood correctly: if we boot with this option core code doesn't use
>> our machine_crash_shutdown(), and instead calls crash_smp_send_stop(), which we
> 
> No. Machine_crash_shutdown() is always called, but at that time,
> all the cpus other than the crashing cpu have already died in this case.
> 

You're right.

>> don't have, so it uses the default smp_send_stop(), which doesn't save the regs.
>> 
>> Thanks for catching this!
>> 
>> 
>> Could we rename smp_send_crash_stop() crash_smp_send_stop() and add the
>> called-twice logic there? They are similar enough that I'm getting them muddled
>> already!
>> 
> 
> Nice.

I'll reflect it in v2.
Thank you for the review.

> 
> -Takahiro AKASHI
> 
>> 
>> Thanks,
>> 
>> James
>> 
>> 
>>> ARM64 architecture uses the weak version function and the problem is that
>>> the weak function simply calls smp_send_stop() which makes other CPUs
>>> offline and takes away the chance to save crash information for nonpanic
>>> CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
>>> option is enabled.
>>> 
>>> Calling smp_send_crash_stop() in the function is useless because all
>>> nonpanic CPUs are already offline by smp_send_stop() in this case and
>>> smp_send_crash_stop() only works against online CPUs.
>>> 
>>> The result is that /proc/vmcore is not available with the error messages;
>>> "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".
>>> 
>>> crash_smp_send_stop() is implemented for ARM64 architecture to fix this
>>> problem and the function (strong symbol version) saves crash information
>>> for nonpanic CPUs using smp_send_crash_stop() and machine_crash_shutdown()
>>> tries to save crash information for nonpanic CPUs only when
>>> crash_kexec_post_notifiers kernel option is disabled.
>> 
>> 

[PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[Hoeun Ryu]

> On 4 Aug 2017, at 7:38 PM, James Morse <james.morse@arm.com> wrote:
> 
> Hi Hoeun,
> 
>> On 04/08/17 08:02, Hoeun Ryu wrote:
>> Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
>> version in panic path) introduced crash_smp_send_stop() which is a weak
>> function and can be overriden by architecture codes to fix the side effect
>> caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
>> notifiers" option).
> 
> If I've understood correctly: if we boot with this option core code doesn't use
> our machine_crash_shutdown(), and instead calls crash_smp_send_stop(), which we
> don't have, so it uses the default smp_send_stop(), which doesn't save the regs.
> 
> Thanks for catching this!
> 
> 
> Could we rename smp_send_crash_stop() crash_smp_send_stop() and add the
> called-twice logic there? They are similar enough that I'm getting them muddled
> already!

I think it is possible, I will reflect it in v2.
Thank you for the review.

> 
> Thanks,
> 
> James
> 
> 
>> ARM64 architecture uses the weak version function and the problem is that
>> the weak function simply calls smp_send_stop() which makes other CPUs
>> offline and takes away the chance to save crash information for nonpanic
>> CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
>> option is enabled.
>> 
>> Calling smp_send_crash_stop() in the function is useless because all
>> nonpanic CPUs are already offline by smp_send_stop() in this case and
>> smp_send_crash_stop() only works against online CPUs.
>> 
>> The result is that /proc/vmcore is not available with the error messages;
>> "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".
>> 
>> crash_smp_send_stop() is implemented for ARM64 architecture to fix this
>> problem and the function (strong symbol version) saves crash information
>> for nonpanic CPUs using smp_send_crash_stop() and machine_crash_shutdown()
>> tries to save crash information for nonpanic CPUs only when
>> crash_kexec_post_notifiers kernel option is disabled.
> 
>