On Tue, Nov 09, 2021 at 05:28:47PM -0300, Guilherme G. Piccoli wrote: > 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. This looks to be helpful for debugging panic. Reviewed-by: Feng Tang <feng.tang@xxxxxxxxx> Thanks, Feng > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> > --- > Documentation/admin-guide/kernel-parameters.txt | 1 + > Documentation/admin-guide/sysctl/kernel.rst | 1 + > kernel/panic.c | 4 ++++ > 3 files changed, 6 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 0905d2cdb2d5..569d035c4332 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3690,6 +3690,7 @@ > 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] > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst > index 70b7df9b081a..1666c1a9dbba 100644 > --- a/Documentation/admin-guide/sysctl/kernel.rst > +++ b/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:: > diff --git a/kernel/panic.c b/kernel/panic.c > index cefd7d82366f..5da71fa4e5f1 100644 > --- a/kernel/panic.c > +++ b/kernel/panic.c > @@ -65,6 +65,7 @@ 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); > @@ -151,6 +152,9 @@ 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(); > > -- > 2.33.1
