commit 838361c6cfb1319eadd59daaf9074dcdb92746e6
Author: Robert Schiele <rschiele@gmail.com>
Date:   Mon Sep 8 09:38:52 2014 +0200

    signal condition variable at end of stop_tracers
    
    stop_tracers modifies tp->is_done and thus must signal the condition
    variable tracer_wait_unblock is waiting on to monitor tp->is_done.
    Not doing so might cause the tool to deadlock if stop_tracers is
    called while a tracer thread is in tracer_wait_unblock.
    
    Signed-off-by: Robert Schiele <rschiele@gmail.com>
    Signed-off-by: Jens Axboe <axboe@fb.com>

diff --git a/blktrace.c b/blktrace.c
index 7e64c94..3c8fb4c 100644
--- a/blktrace.c
+++ b/blktrace.c
@@ -1913,6 +1913,7 @@ static void stop_tracers(void)
 		struct tracer *tp = list_entry(p, struct tracer, head);
 		tp->is_done = 1;
 	}
+	pthread_cond_broadcast(&mt_cond);
 }
 
 static void del_tracers(void)