From: Rik van Riel SysRQ-P is not always useful on SMP systems, since it usually ends up showing the backtrace of a CPU that is doing just fine, instead of the backtrace of the CPU that is having problems. This patch adds SysRQ show-all-cpus(L), which shows the backtrace of every active CPU in the system. It skips idle CPUs because some SMP systems are just too large and we already know what the backtrace of the idle task looks like. Signed-off-by: Rik van Riel Randy Dunlap Cc: Cc: Ingo Molnar Signed-off-by: Andrew Morton --- Documentation/sysrq.txt | 2 + drivers/char/sysrq.c | 42 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+) diff -puN Documentation/sysrq.txt~sysrq-add-show-backtrace-on-all-cpus-function Documentation/sysrq.txt --- a/Documentation/sysrq.txt~sysrq-add-show-backtrace-on-all-cpus-function +++ a/Documentation/sysrq.txt @@ -85,6 +85,8 @@ On all - write a character to /proc/sys 'k' - Secure Access Key (SAK) Kills all programs on the current virtual console. NOTE: See important comments below in SAK section. +'l' - Shows a stack backtrace for all active CPUs. + 'm' - Will dump current memory info to your console. 'n' - Used to make RT tasks nice-able diff -puN drivers/char/sysrq.c~sysrq-add-show-backtrace-on-all-cpus-function drivers/char/sysrq.c --- a/drivers/char/sysrq.c~sysrq-add-show-backtrace-on-all-cpus-function +++ a/drivers/char/sysrq.c @@ -196,6 +196,44 @@ static struct sysrq_key_op sysrq_showloc #define sysrq_showlocks_op (*(struct sysrq_key_op *)0) #endif +#ifdef CONFIG_SMP +static DEFINE_SPINLOCK(show_lock); +static void showacpu(void *dummy) +{ + unsigned long flags; + + /* Idle CPUs have no interesting backtrace. */ + if (idle_cpu(smp_processor_id())) + return; + + spin_lock_irqsave(&show_lock, flags); + printk("CPU%d:\n", smp_processor_id()); + show_stack(NULL, NULL); + spin_unlock_irqrestore(&show_lock, flags); +} +static void sysrq_showregs_othercpus(struct work_struct *dummy) +{ + smp_call_function(showacpu, NULL, 0, 0); +} +static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus); + +static void sysrq_handle_showallcpus(int key, struct tty_struct *tty) +{ + struct pt_regs *regs = get_irq_regs(); + if (regs) { + printk("CPU%d:\n", smp_processor_id()); + show_regs(regs); + } + schedule_work(&sysrq_showallcpus); +} +static struct sysrq_key_op sysrq_showallcpus_op = { + .handler = sysrq_handle_showallcpus, + .help_msg = "aLlcpus", + .action_msg = "Show backtrace of all active CPUs", + .enable_mask = SYSRQ_ENABLE_DUMP, +}; +#endif + static void sysrq_handle_showregs(int key, struct tty_struct *tty) { struct pt_regs *regs = get_irq_regs(); @@ -340,7 +378,11 @@ static struct sysrq_key_op *sysrq_key_ta &sysrq_kill_op, /* i */ NULL, /* j */ &sysrq_SAK_op, /* k */ +#ifdef CONFIG_SMP + &sysrq_showallcpus_op, /* l */ +#else NULL, /* l */ +#endif &sysrq_showmem_op, /* m */ &sysrq_unrt_op, /* n */ /* o: This will often be registered as 'Off' at init time */ _