Commit 0f6ce3de authored Jun 01, 2009 by Steven Rostedt Committed by Steven Rostedt Jun 01, 2009

ftrace: do not profile functions when disabled



A race was found that if one were to enable and disable the function
profiler repeatedly, then the system can panic. This was because a profiled
function may be preempted just before disabling interrupts. While
the profiler is disabled and then reenabled, the preempted function
could start again, and access the hash as it is being initialized.

This just adds a check in the irq disabled part to check if the profiler
is enabled, and if it is not then it will just exit.

When the system is disabled, the profile_enabled variable is cleared
before calling the unregistering of the function profiler. This
unregistering calls stop machine which also acts as a synchronize schedule.

[ Impact: fix panic in enabling/disabling function profiler ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

parent 112f38a7

kernel/trace/ftrace.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -599,7 +599,7 @@ function_profile_call(unsigned long ip, unsigned long parent_ip)
		local_irq_save(flags);

		stat = &__get_cpu_var(ftrace_profile_stats);
		if (!stat->hash)
		if (!stat->hash \|\| !ftrace_profile_enabled)
		goto out;

		rec = ftrace_find_profiled_func(stat, ip);
		@@ -630,7 +630,7 @@ static void profile_graph_return(struct ftrace_graph_ret *trace)

		local_irq_save(flags);
		stat = &__get_cpu_var(ftrace_profile_stats);
		if (!stat->hash)
		if (!stat->hash \|\| !ftrace_profile_enabled)
		goto out;

		calltime = trace->rettime - trace->calltime;
		@@ -724,6 +724,10 @@ ftrace_profile_write(struct file filp, const char __user ubuf,
		ftrace_profile_enabled = 1;
		} else {
		ftrace_profile_enabled = 0;
		/*
		* unregister_ftrace_profiler calls stop_machine
		* so this acts like an synchronize_sched.
		*/
		unregister_ftrace_profiler();
		}
		}

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