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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@igalia.com
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Reviewed-by: Feng Tang <feng.tang@intel.com>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Guilherme G. Piccoli 2022-03-23 16:07:06 -07:00 committed by Linus Torvalds
parent a1ff1de00d
commit 8d470a45d1
3 changed files with 6 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
Documentation/admin-guide/kernel-parameters.txt
View File

@ -3726,6 +3726,7 @@
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]

1
Documentation/admin-guide/sysctl/kernel.rst
View File

@ -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::

4
kernel/panic.c
View File

@ -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();