tracing: Fix circular dead lock in stack trace (4f48f8b7) · Commits · 戴 / test

When we cat <debugfs>/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 <lizf@cn.fujitsu.com> Signed-off-by:

Lai Jiangshan <laijs@cn.fujitsu.com> LKML-Reference: <4B67D4F9.9080905@cn.fujitsu.com> Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace_stack.c

+24 −0

Original line number	Diff line number	Diff line
		@@ -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();
		}

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