From 67f2de0bf9141dd9fe9189d0caaa28d7ad21a523 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Thu, 26 Nov 2009 08:29:10 +0100 Subject: [PATCH] x86: dumpstack, 64-bit: Disable preemption when walking the IRQ/exception stacks This warning: [ 847.140022] rb_producer D 0000000000000000 5928 519 2 0x00000000 [ 847.203627] BUG: using smp_processor_id() in preemptible [00000000] code: khungtaskd/517 [ 847.207360] caller is show_stack_log_lvl+0x2e/0x241 [ 847.210364] Pid: 517, comm: khungtaskd Not tainted 2.6.32-rc8-tip+ #13761 [ 847.213395] Call Trace: [ 847.215847] [] debug_smp_processor_id+0x1f0/0x20a [ 847.216809] [] show_stack_log_lvl+0x2e/0x241 [ 847.220027] [] show_stack+0x1c/0x1e [ 847.223365] [] sched_show_task+0xe4/0xe9 [ 847.226694] [] check_hung_task+0x140/0x199 [ 847.230261] [] check_hung_uninterruptible_tasks+0x1b7/0x20f [ 847.233371] [] ? watchdog+0x0/0x50 [ 847.236683] [] watchdog+0x4e/0x50 [ 847.240034] [] kthread+0x97/0x9f [ 847.243372] [] child_rip+0xa/0x20 [ 847.246690] [] ? restore_args+0x0/0x30 [ 847.250019] [] ? _spin_lock+0xe/0x10 [ 847.253351] [] ? kthread+0x0/0x9f [ 847.256833] [] ? child_rip+0x0/0x20 Happens because on preempt-RCU, khungd calls show_stack() with preemption enabled. Make sure we are not preemptible while walking the IRQ and exception stacks on 64-bit. (32-bit stack dumping is preemption safe.) Signed-off-by: Ingo Molnar --- arch/x86/kernel/dumpstack_64.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c index cfec478a4e42..8e740934bd1f 100644 --- a/arch/x86/kernel/dumpstack_64.c +++ b/arch/x86/kernel/dumpstack_64.c @@ -206,19 +206,22 @@ void show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs, unsigned long *sp, unsigned long bp, char *log_lvl) { + unsigned long *irq_stack_end; + unsigned long *irq_stack; unsigned long *stack; + int cpu; int i; - const int cpu = smp_processor_id(); - unsigned long *irq_stack_end = - (unsigned long *)(per_cpu(irq_stack_ptr, cpu)); - unsigned long *irq_stack = - (unsigned long *)(per_cpu(irq_stack_ptr, cpu) - IRQ_STACK_SIZE); + + preempt_disable(); + cpu = smp_processor_id(); + + irq_stack_end = (unsigned long *)(per_cpu(irq_stack_ptr, cpu)); + irq_stack = (unsigned long *)(per_cpu(irq_stack_ptr, cpu) - IRQ_STACK_SIZE); /* - * debugging aid: "show_stack(NULL, NULL);" prints the - * back trace for this cpu. + * Debugging aid: "show_stack(NULL, NULL);" prints the + * back trace for this cpu: */ - if (sp == NULL) { if (task) sp = (unsigned long *)task->thread.sp; @@ -242,6 +245,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs, printk(" %016lx", *stack++); touch_nmi_watchdog(); } + preempt_enable(); + printk("\n"); show_trace_log_lvl(task, regs, sp, bp, log_lvl); }