[PATCH v4 0/3] Introduce arch_do_panic

[PATCH v4 0/3] Introduce arch_do_panic

[Mete Durlu]

Changes in v4:
- Remove s390 specific behavior changes and limit the series with
  cosmetic clean ups and introduction of arch_do_panic()
  (Heiko Carstens)
- Include linux/panic.h on files where arch_do_panic() is implemented
  (Sashiko)
- Remove extern "stop_a_enabled" definition from sparc's arch_do_panic()
  implementation as it is already visible by included asm/setup.h
  (Sashiko)
- Include "linux/printk.h" header on sparc/setup.c explicitly for
  pr_emerg() (Sashiko)

Changes in v3:
- Use __weak functions instead of symbol override via ifdef
- Patch 2: Better explain what is fixed (Bradley Morgan)
- Add statements about print order changes (Bradley Morgan)
- Patch 2: Add a pr_warn() to notify user about on_panic and
  panic_timeout relationship if they try to assign a trigger to
  on_panic action while panic_timeout is set to a value other than 0
  (Bradley Morgan)

Changes in v2 - Address Sashiko findings;
- Patch 2: Remove unused leftover code
- Patch 2: Mention panic_timeout and shutdown_actions relationship for
  s390 in commit message
- Patch 3: Use bug.h instead of setup.h to pass around arch_do_panic
  implementation of sparc

A note before coverletter:
On earlier versions I attempted to move s390s panic handler into
arch_do_panic() but the interaction between panic handler and kernel's
panic_timeout had become implicit and suboptimal. After reading Heiko's
comments I have decided to tackle that in a separate series and keep
this one limited to a smaller set of changes.
-------

Replace architecture-specific ifdef sections in vpanic() with a clean
arch_do_panic() hook. Currently s390 and sparc embed their panic
handlers directly in vpanic() using preprocessor conditionals, making
the common code path harder to maintain.

Introduce arch_do_panic() as an architecture extension point called at
the end of vpanic(). Architectures can use this hook to implement their
specific panic handling without polluting the generic panic code.

Remove s390s ifdef block in vpanic() and move the corresponding code
block to s390s own arch_do_panic() implementation in architecture
specific code.

Move sparc panic handling from ifdef blocks to arch_do_panic(). Remove
the preprocessor conditionals from vpanic() and place the Stop-A
enablement code in architecture-specific files where it belongs.
Stop-A enablement markers are now printed after "end Kernel panic"
line.

The cleanup reduces vpanic() complexity and establishes a pattern for other
architectures needing custom panic behavior.
No functional changes.

Signed-off-by: Mete Durlu <meted@linux.ibm.com>
---
Mete Durlu (3):
      panic: Introduce arch_do_panic
      s390: Implement arch_do_panic()
      sparc: Implement arch_do_panic

 arch/s390/kernel/ipl.c    |  6 ++++++
 arch/sparc/kernel/setup.c |  9 +++++++++
 include/linux/panic.h     |  2 ++
 kernel/panic.c            | 15 +++------------
 4 files changed, 20 insertions(+), 12 deletions(-)
---
base-commit: 48a5a7ab8d6ab7090564339e039c421f315de912
change-id: 20260724-arch_do_panic-a97f699aa332

Best regards,
-- 
Mete Durlu <meted@linux.ibm.com>

[PATCH v4 1/3] panic: Introduce arch_do_panic

[Mete Durlu]

Introduce a hook for architectures to put their specific panic handlers.
s390 and sparc already has ifdef preprocessor checks to execute
architecture specific code. Pave the way for vpanic() cleanup.

Reviewed-by: Bradley Morgan <include@grrlz.net>
Suggested-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Mete Durlu <meted@linux.ibm.com>
---
 include/linux/panic.h | 2 ++
 kernel/panic.c        | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/include/linux/panic.h b/include/linux/panic.h
index f1dd417e54b2..98dd7dfd27de 100644
--- a/include/linux/panic.h
+++ b/include/linux/panic.h
@@ -110,4 +110,6 @@ extern void add_taint(unsigned flag, enum lockdep_ok);
 extern int test_taint(unsigned flag);
 extern unsigned long get_taint(void);
 
+void arch_do_panic(void);
+
 #endif	/* _LINUX_PANIC_H */
diff --git a/kernel/panic.c b/kernel/panic.c
index 213725b612aa..726a97842232 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -567,6 +567,8 @@ static void panic_other_cpus_shutdown(bool crash_kexec)
 		crash_smp_send_stop();
 }
 
+void __weak arch_do_panic(void) {}
+
 /**
  * vpanic - halt the system
  * @fmt: The text string to print
@@ -756,6 +758,7 @@ void vpanic(const char *fmt, va_list args)
 #endif
 	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
 
+	arch_do_panic();
 	/* Do not scroll important messages printed above */
 	suppress_printk = 1;
 

-- 
2.55.0

Re: [PATCH v4 1/3] panic: Introduce arch_do_panic

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The newly introduced `arch_do_panic()` hook is placed before the explicit console flushes. On architectures that halt indefinitely within this hook (e.g., s390), the final 'end Kernel panic' message and any deferred NMI logs will be lost because the required explicit flush is never executed.
--

--- Patch [1]: [PATCH v4 1/3] panic: Introduce arch_do_panic ---
commit 6fe8c46d4a07969ba51a615fab55e7ba7120f254
Author: Mete Durlu <meted@linux.ibm.com>

panic: Introduce arch_do_panic

This patch introduces a weak hook for architectures to provide their
specific panic handlers. This aims to help clean up architecture specific
ifdef checks in the panic path.

> diff --git a/kernel/panic.c b/kernel/panic.c
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
[ ... ]
> @@ -756,6 +758,7 @@ void vpanic(const char *fmt, va_list args)
>  #endif
>  	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
>  
> +	arch_do_panic();

[Severity: Medium]
If an architecture implements this hook and halts indefinitely, will this
bypass the final explicit console flushes?

The final explicit flush happens shortly after this addition:

vpanic() {
    ...
    pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
    arch_do_panic();
    suppress_printk = 1;

    console_flush_on_panic(CONSOLE_FLUSH_PENDING);
    nbcon_atomic_flush_unsafe();
    ...
}

Could this cause deferred log messages, such as NMI backtraces or the final
panic banner, to be lost because the required explicit flush is never executed?

>  	/* Do not scroll important messages printed above */
>  	suppress_printk = 1;
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260805-arch_do_panic-v4-0-af4a36f99414@linux.ibm.com?part=1

[PATCH v4 2/3] s390: Implement arch_do_panic()

[Mete Durlu]

Implement s390 specific arch_do_panic() instead of using s390 specific
ifdef sections in vpanic() code.
No functional changes.

Signed-off-by: Mete Durlu <meted@linux.ibm.com>
---
 arch/s390/kernel/ipl.c | 6 ++++++
 kernel/panic.c         | 3 ---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/s390/kernel/ipl.c b/arch/s390/kernel/ipl.c
index 3c346b02ceb9..31ff7c12c354 100644
--- a/arch/s390/kernel/ipl.c
+++ b/arch/s390/kernel/ipl.c
@@ -13,6 +13,7 @@
 #include <linux/device.h>
 #include <linux/delay.h>
 #include <linux/kstrtox.h>
+#include <linux/panic.h>
 #include <linux/panic_notifier.h>
 #include <linux/reboot.h>
 #include <linux/ctype.h>
@@ -2343,6 +2344,11 @@ static struct notifier_block on_panic_nb = {
 	.priority = INT_MIN,
 };
 
+void arch_do_panic(void)
+{
+	disabled_wait();
+}
+
 void __init setup_ipl(void)
 {
 	BUILD_BUG_ON(sizeof(struct ipl_parameter_block) != PAGE_SIZE);
diff --git a/kernel/panic.c b/kernel/panic.c
index 726a97842232..ee6e3f9e3900 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -752,9 +752,6 @@ void vpanic(const char *fmt, va_list args)
 		pr_emerg("Press Stop-A (L1-A) from sun keyboard or send break\n"
 			 "twice on console to return to the boot prom\n");
 	}
-#endif
-#if defined(CONFIG_S390)
-	disabled_wait();
 #endif
 	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
 

-- 
2.55.0

Re: [PATCH v4 2/3] s390: Implement arch_do_panic()

[sashiko-bot]

> Implement s390 specific arch_do_panic() instead of using s390 specific
> ifdef sections in vpanic() code.
> No functional changes.
> 
> Signed-off-by: Mete Durlu <meted@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260805-arch_do_panic-v4-0-af4a36f99414@linux.ibm.com?part=2

Re: [PATCH v4 2/3] s390: Implement arch_do_panic()

[Heiko Carstens]

On Wed, Aug 05, 2026 at 11:48:37AM +0200, Mete Durlu wrote:
> Implement s390 specific arch_do_panic() instead of using s390 specific
> ifdef sections in vpanic() code.
> No functional changes.
> 
> Signed-off-by: Mete Durlu <meted@linux.ibm.com>
> ---
>  arch/s390/kernel/ipl.c | 6 ++++++
>  kernel/panic.c         | 3 ---
>  2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/kernel/ipl.c b/arch/s390/kernel/ipl.c
> index 3c346b02ceb9..31ff7c12c354 100644
> --- a/arch/s390/kernel/ipl.c
> +++ b/arch/s390/kernel/ipl.c
> @@ -13,6 +13,7 @@
>  #include <linux/device.h>
>  #include <linux/delay.h>
>  #include <linux/kstrtox.h>
> +#include <linux/panic.h>
>  #include <linux/panic_notifier.h>
>  #include <linux/reboot.h>
>  #include <linux/ctype.h>
> @@ -2343,6 +2344,11 @@ static struct notifier_block on_panic_nb = {
>  	.priority = INT_MIN,
>  };
>  
> +void arch_do_panic(void)
> +{
> +	disabled_wait();
> +}
> +

Please move this to arch/s390/kernel/traps.c somewhere near
kernel_stack_invalid() and monitor_event_exception().

Re: [PATCH v4 2/3] s390: Implement arch_do_panic()

[Mete Durlu]

On 05/08/2026 12:06, Heiko Carstens wrote:
> On Wed, Aug 05, 2026 at 11:48:37AM +0200, Mete Durlu wrote:
>> Implement s390 specific arch_do_panic() instead of using s390 specific
>> ifdef sections in vpanic() code.
>> No functional changes.
>>
>> Signed-off-by: Mete Durlu <meted@linux.ibm.com>
>> ---
>>   arch/s390/kernel/ipl.c | 6 ++++++
>>   kernel/panic.c         | 3 ---
>>   2 files changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/s390/kernel/ipl.c b/arch/s390/kernel/ipl.c
>> index 3c346b02ceb9..31ff7c12c354 100644
>> --- a/arch/s390/kernel/ipl.c
>> +++ b/arch/s390/kernel/ipl.c
>> @@ -13,6 +13,7 @@
>>   #include <linux/device.h>
>>   #include <linux/delay.h>
>>   #include <linux/kstrtox.h>
>> +#include <linux/panic.h>
>>   #include <linux/panic_notifier.h>
>>   #include <linux/reboot.h>
>>   #include <linux/ctype.h>
>> @@ -2343,6 +2344,11 @@ static struct notifier_block on_panic_nb = {
>>   	.priority = INT_MIN,
>>   };
>>   
>> +void arch_do_panic(void)
>> +{
>> +	disabled_wait();
>> +}
>> +
> 
> Please move this to arch/s390/kernel/traps.c somewhere near
> kernel_stack_invalid() and monitor_event_exception().

Alright, will do in the next version.
Thank you for having a look!

[PATCH v4 3/3] sparc: Implement arch_do_panic

[Mete Durlu]

Implement sparc specific arch_do_panic() instead of using sparc specific
ifdef sections in vpanic() code.
Reorder arch specific panic handling, sparc's Stop-A messages are now
printed after "end Kernel panic" marker.

Signed-off-by: Mete Durlu <meted@linux.ibm.com>
---
 arch/sparc/kernel/setup.c | 9 +++++++++
 kernel/panic.c            | 9 ---------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/sparc/kernel/setup.c b/arch/sparc/kernel/setup.c
index 4975867d9001..5f43cef80638 100644
--- a/arch/sparc/kernel/setup.c
+++ b/arch/sparc/kernel/setup.c
@@ -2,6 +2,8 @@
 
 #include <asm/setup.h>
 #include <linux/sysctl.h>
+#include <linux/panic.h>
+#include <linux/printk.h>
 
 static const struct ctl_table sparc_sysctl_table[] = {
 	{
@@ -36,6 +38,13 @@ static const struct ctl_table sparc_sysctl_table[] = {
 #endif
 };
 
+void arch_do_panic(void)
+{
+	/* Make sure the user can actually press Stop-A (L1-A) */
+	stop_a_enabled = 1;
+	pr_emerg("Press Stop-A (L1-A) from sun keyboard or send break\n"
+		 "twice on console to return to the boot prom\n");
+}
 
 static int __init init_sparc_sysctls(void)
 {
diff --git a/kernel/panic.c b/kernel/panic.c
index ee6e3f9e3900..7dda841c16f9 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -744,15 +744,6 @@ void vpanic(const char *fmt, va_list args)
 			reboot_mode = panic_reboot_mode;
 		emergency_restart();
 	}
-#ifdef __sparc__
-	{
-		extern int stop_a_enabled;
-		/* Make sure the user can actually press Stop-A (L1-A) */
-		stop_a_enabled = 1;
-		pr_emerg("Press Stop-A (L1-A) from sun keyboard or send break\n"
-			 "twice on console to return to the boot prom\n");
-	}
-#endif
 	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
 
 	arch_do_panic();

-- 
2.55.0

Re: [PATCH v4 3/3] sparc: Implement arch_do_panic

[sashiko-bot]

> Implement sparc specific arch_do_panic() instead of using sparc specific
> ifdef sections in vpanic() code.
> Reorder arch specific panic handling, sparc's Stop-A messages are now
> printed after "end Kernel panic" marker.
> 
> Signed-off-by: Mete Durlu <meted@linux.ibm.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260805-arch_do_panic-v4-0-af4a36f99414@linux.ibm.com?part=3