From: Ingo Molnar Improve the debuggability of kernel lockups by enhancing the debug output of the softlockup detector: print the task that causes the lockup and try to print a more intelligent backtrace. The old format was: BUG: soft lockup detected on CPU#1! [] show_trace_log_lvl+0x19/0x2e [] show_trace+0x12/0x14 [] dump_stack+0x14/0x16 [] softlockup_tick+0xbe/0xd0 [] run_local_timers+0x12/0x14 [] update_process_times+0x3e/0x63 [] tick_sched_timer+0x7c/0xc0 [] hrtimer_interrupt+0x135/0x1ba [] smp_apic_timer_interrupt+0x6e/0x80 [] apic_timer_interrupt+0x33/0x38 [] syscall_call+0x7/0xb ======================= The new format is: BUG: soft lockup detected on CPU#1! [prctl:2363] Pid: 2363, comm: prctl EIP: 0060:[] CPU: 1 EIP is at sys_prctl+0x24/0x18c EFLAGS: 00000213 Not tainted (2.6.22-cfs-v20 #26) EAX: 00000001 EBX: 000003e7 ECX: 00000001 EDX: f6df0000 ESI: 000003e7 EDI: 000003e7 EBP: f6df0fb0 DS: 007b ES: 007b FS: 00d8 CR0: 8005003b CR2: 4d8c3340 CR3: 3731d000 CR4: 000006d0 [] show_trace_log_lvl+0x19/0x2e [] show_trace+0x12/0x14 [] show_regs+0x1ab/0x1b3 [] softlockup_tick+0xef/0x108 [] run_local_timers+0x12/0x14 [] update_process_times+0x3e/0x63 [] tick_sched_timer+0x7c/0xc0 [] hrtimer_interrupt+0x135/0x1ba [] smp_apic_timer_interrupt+0x6e/0x80 [] apic_timer_interrupt+0x33/0x38 [] syscall_call+0x7/0xb ======================= Note that in the old format we only knew that some system call locked up, we didnt know _which_. With the new format we know that it's at a specific place in sys_prctl(). [which was where i created an artificial kernel lockup to test the new format.] This is also useful if the lockup happens in user-space - the user-space EIP (and other registers) will be printed too. (such a lockup would either suggest that the task was running at SCHED_FIFO:99 and looping for more than 10 seconds, or that the softlockup detector has a false-positive.) The task name is printed too first, just in case we dont manage to print a useful backtrace. Signed-off-by: Ingo Molnar Signed-off-by: Andrew Morton --- kernel/softlockup.c | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) diff -puN kernel/softlockup.c~softlockup-improve-debug-output kernel/softlockup.c --- a/kernel/softlockup.c~softlockup-improve-debug-output +++ a/kernel/softlockup.c @@ -16,6 +16,8 @@ #include #include +#include + static DEFINE_SPINLOCK(print_lock); static DEFINE_PER_CPU(unsigned long, touch_timestamp); @@ -77,6 +79,7 @@ void softlockup_tick(void) int this_cpu = smp_processor_id(); unsigned long touch_timestamp = per_cpu(touch_timestamp, this_cpu); unsigned long print_timestamp; + struct pt_regs *regs; unsigned long now; if (touch_timestamp == 0) { @@ -106,19 +109,22 @@ void softlockup_tick(void) wake_up_process(per_cpu(watchdog_task, this_cpu)); /* Warn about unreasonable 10+ seconds delays: */ - if (now > (touch_timestamp + 10)) { + if (now <= (touch_timestamp + 10)) + return; #ifdef CONFIG_KGDB - if (unlikely(kgdb_softlock_skip[this_cpu])) - return; + if (unlikely(kgdb_softlock_skip[this_cpu])) + return; #endif - per_cpu(print_timestamp, this_cpu) = touch_timestamp; + per_cpu(print_timestamp, this_cpu) = touch_timestamp; - spin_lock(&print_lock); - printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n", - this_cpu); + spin_lock(&print_lock); + printk(KERN_ERR "BUG: soft lockup detected on CPU#%d! [%s:%d]\n", + this_cpu, current->comm, current->pid); + if (regs) + show_regs(regs); + else dump_stack(); - spin_unlock(&print_lock); - } + spin_unlock(&print_lock); } /* _