The patch titled
Subject: panic: add option to dump all CPUs backtraces in panic_print
has been added to the -mm tree. Its filename is
panic-add-option-to-dump-all-cpus-backtraces-in-panic_print.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/panic-add-option-to-dump-all-cpus-backtraces-in-panic_print.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/panic-add-option-to-dump-all-cpus-backtraces-in-panic_print.patch
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------------------------------------------------------
From: "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>
Subject: panic: add option to dump all CPUs backtraces in panic_print
Currently the "panic_print" parameter/sysctl allows some interesting debug
information to be printed during a panic event. This is useful for
example in cases the user cannot kdump due to resource limits, or if the
user collects panic logs in a serial output (or pstore) and prefers a fast
reboot instead of a kdump.
Happens that currently there's no way to see all CPUs backtraces in a
panic using "panic_print" on architectures that support that. We do have
"oops_all_cpu_backtrace" sysctl, but although partially overlapping in the
functionality, they are orthogonal in nature: "panic_print" is a panic
tuning (and we have panics without oopses, like direct calls to panic() or
maybe other paths that don't go through oops_enter() function), and the
original purpose of "oops_all_cpu_backtrace" is to provide more
information on oopses for cases in which the users desire to continue
running the kernel even after an oops, i.e., used in non-panic scenarios.
So, we hereby introduce an additional bit for "panic_print" to allow
dumping the CPUs backtraces during a panic event.
Link: https://lkml.kernel.org/r/20211109202848.610874-3-gpiccoli@xxxxxxxxxx
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
Reviewed-by: Feng Tang <feng.tang@xxxxxxxxx>
Cc: Iurii Zaikin <yzaikin@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Samuel Iglesias Gonsalvez <siglesias@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/kernel-parameters.txt | 1 +
Documentation/admin-guide/sysctl/kernel.rst | 1 +
kernel/panic.c | 4 ++++
3 files changed, 6 insertions(+)
--- a/Documentation/admin-guide/kernel-parameters.txt~panic-add-option-to-dump-all-cpus-backtraces-in-panic_print
+++ a/Documentation/admin-guide/kernel-parameters.txt
@@ -3704,6 +3704,7 @@
bit 3: print locks info if CONFIG_LOCKDEP is on
bit 4: print ftrace buffer
bit 5: print all printk messages in buffer
+ bit 6: print all CPUs backtrace (if available in the arch)
panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
Format: <hex>[,nousertaint]
--- a/Documentation/admin-guide/sysctl/kernel.rst~panic-add-option-to-dump-all-cpus-backtraces-in-panic_print
+++ a/Documentation/admin-guide/sysctl/kernel.rst
@@ -796,6 +796,7 @@ bit 2 print timer info
bit 3 print locks info if ``CONFIG_LOCKDEP`` is on
bit 4 print ftrace buffer
bit 5: print all printk messages in buffer
+bit 6: print all CPUs backtrace (if available in the arch)
===== ============================================
So for example to print tasks and memory info on panic, user can::
--- a/kernel/panic.c~panic-add-option-to-dump-all-cpus-backtraces-in-panic_print
+++ a/kernel/panic.c
@@ -66,6 +66,7 @@ EXPORT_SYMBOL_GPL(panic_timeout);
#define PANIC_PRINT_LOCK_INFO 0x00000008
#define PANIC_PRINT_FTRACE_INFO 0x00000010
#define PANIC_PRINT_ALL_PRINTK_MSG 0x00000020
+#define PANIC_PRINT_ALL_CPU_BT 0x00000040
unsigned long panic_print;
ATOMIC_NOTIFIER_HEAD(panic_notifier_list);
@@ -152,6 +153,9 @@ static void panic_print_sys_info(void)
if (panic_print & PANIC_PRINT_ALL_PRINTK_MSG)
console_flush_on_panic(CONSOLE_REPLAY_ALL);
+ if (panic_print & PANIC_PRINT_ALL_CPU_BT)
+ trigger_all_cpu_backtrace();
+
if (panic_print & PANIC_PRINT_TASK_INFO)
show_state();
_
Patches currently in -mm which might be from gpiccoli@xxxxxxxxxx are
docs-sysctl-kernel-add-missing-bit-to-panic_print.patch
panic-add-option-to-dump-all-cpus-backtraces-in-panic_print.patch
panic-allow-printing-extra-panic-information-on-kdump.patch
