From 4f48f8b7fd18c44f8478174f9925cc3c059c6ce4 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Tue, 2 Feb 2010 15:32:09 +0800 Subject: tracing: Fix circular dead lock in stack trace When we cat /tracing/stack_trace, we may cause circular lock: sys_read() t_start() arch_spin_lock(&max_stack_lock); t_show() seq_printf(), vsnprintf() .... /* they are all trace-able, when they are traced, max_stack_lock may be required again. */ The following script can trigger this circular dead lock very easy: #!/bin/bash echo 1 > /proc/sys/kernel/stack_tracer_enabled mount -t debugfs xxx /mnt > /dev/null 2>&1 ( # make check_stack() zealous to require max_stack_lock for ((; ;)) { echo 1 > /mnt/tracing/stack_max_size } ) & for ((; ;)) { cat /mnt/tracing/stack_trace > /dev/null } To fix this bug, we increase the percpu trace_active before require the lock. Reported-by: Li Zefan Signed-off-by: Lai Jiangshan LKML-Reference: <4B67D4F9.9080905@cn.fujitsu.com> Signed-off-by: Steven Rostedt --- kernel/trace/trace_stack.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c index 678a5120ee30..f4bc9b27de5f 100644 --- a/kernel/trace/trace_stack.c +++ b/kernel/trace/trace_stack.c @@ -157,6 +157,7 @@ stack_max_size_write(struct file *filp, const char __user *ubuf, unsigned long val, flags; char buf[64]; int ret; + int cpu; if (count >= sizeof(buf)) return -EINVAL; @@ -171,9 +172,20 @@ stack_max_size_write(struct file *filp, const char __user *ubuf, return ret; local_irq_save(flags); + + /* + * In case we trace inside arch_spin_lock() or after (NMI), + * we will cause circular lock, so we also need to increase + * the percpu trace_active here. + */ + cpu = smp_processor_id(); + per_cpu(trace_active, cpu)++; + arch_spin_lock(&max_stack_lock); *ptr = val; arch_spin_unlock(&max_stack_lock); + + per_cpu(trace_active, cpu)--; local_irq_restore(flags); return count; @@ -206,7 +218,13 @@ t_next(struct seq_file *m, void *v, loff_t *pos) static void *t_start(struct seq_file *m, loff_t *pos) { + int cpu; + local_irq_disable(); + + cpu = smp_processor_id(); + per_cpu(trace_active, cpu)++; + arch_spin_lock(&max_stack_lock); if (*pos == 0) @@ -217,7 +235,13 @@ static void *t_start(struct seq_file *m, loff_t *pos) static void t_stop(struct seq_file *m, void *p) { + int cpu; + arch_spin_unlock(&max_stack_lock); + + cpu = smp_processor_id(); + per_cpu(trace_active, cpu)--; + local_irq_enable(); } -- cgit v1.2.3