From 10dd3ebe213c31bff14b4dae3c5d32a76b1fad7c Mon Sep 17 00:00:00 2001 From: KOSAKI Motohiro Date: Fri, 6 Mar 2009 15:29:04 +0900 Subject: [PATCH] tracing: fix deadlock when setting set_ftrace_pid Impact: fix deadlock while using set_ftrace_pid Reproducer: # cd /sys/kernel/debug/tracing # echo $$ > set_ftrace_pid then, console becomes hung. Details: when writing set_ftracepid, kernel callstack is following ftrace_pid_write() mutex_lock(&ftrace_lock); ftrace_update_pid_func() mutex_lock(&ftrace_lock); mutex_unlock(&ftrace_lock); mutex_unlock(&ftrace_lock); then, system always deadlocks when ftrace_pid_write() is called. In past days, ftrace_pid_write() used ftrace_start_lock, but commit e6ea44e9b4c12325337cd1c06103cd515a1c02b2 consolidated ftrace_start_lock to ftrace_lock. Signed-off-by: KOSAKI Motohiro Reviewed-by: Lai Jiangshan Cc: Steven Rostedt LKML-Reference: <20090306151155.0778.A69D9226@jp.fujitsu.com> Signed-off-by: Ingo Molnar --- kernel/trace/ftrace.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index d7a06a0d9447..d33d306bdcf4 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -218,10 +218,8 @@ static void ftrace_update_pid_func(void) { ftrace_func_t func; - mutex_lock(&ftrace_lock); - if (ftrace_trace_function == ftrace_stub) - goto out; + return; func = ftrace_trace_function; @@ -238,9 +236,6 @@ static void ftrace_update_pid_func(void) #else __ftrace_trace_function = func; #endif - - out: - mutex_unlock(&ftrace_lock); } /* set when tracing only a pid */