tracing: Fix lock inversion in trace_event_enable_tgid_record()

       Task T2                             Task T3
trace_options_core_write()            subsystem_open()

 mutex_lock(trace_types_lock)           mutex_lock(event_mutex)

 set_tracer_flag()

   trace_event_enable_tgid_record()       mutex_lock(trace_types_lock)

    mutex_lock(event_mutex)

This gives a circular dependency deadlock between trace_types_lock and
event_mutex. To fix this invert the usage of trace_types_lock and
event_mutex in trace_options_core_write(). This keeps the sequence of
lock usage consistent.

Link: http://lkml.kernel.org/r/0101016eef175e38-8ca71caf-a4eb-480d-a1e6-6f0bbc015495-000000@us-west-2.amazonses.com
Cc: stable@vger.kernel.org
Fixes: a6c900751f23f ("tracing: Add support for recording tgid of tasks")
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6c75410f96988fa887d10a2bbb933890211fcde5..ddb7e7f5fe8d8316b73f1c163bd7a3c894735e5a 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4685,6 +4685,10 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)
 
 int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
 {
+       if ((mask == TRACE_ITER_RECORD_TGID) ||
+           (mask == TRACE_ITER_RECORD_CMD))
+               lockdep_assert_held(&event_mutex);
+
        /* do nothing if flag is already set */
        if (!!(tr->trace_flags & mask) == !!enabled)
                return 0;
@@ -4752,6 +4756,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
 
        cmp += len;
 
+       mutex_lock(&event_mutex);
        mutex_lock(&trace_types_lock);
 
        ret = match_string(trace_options, -1, cmp);
@@ -4762,6 +4767,7 @@ static int trace_set_options(struct trace_array *tr, char *option)
                ret = set_tracer_flag(tr, 1 << ret, !neg);
 
        mutex_unlock(&trace_types_lock);
+       mutex_unlock(&event_mutex);
 
        /*
         * If the first trailing whitespace is replaced with '\0' by strstrip,
@@ -8076,9 +8082,11 @@ trace_options_core_write(struct file *filp, const char __user *ubuf, size_t cnt,
        if (val != 0 && val != 1)
                return -EINVAL;
 
+       mutex_lock(&event_mutex);
        mutex_lock(&trace_types_lock);
        ret = set_tracer_flag(tr, 1 << index, val);
        mutex_unlock(&trace_types_lock);
+       mutex_unlock(&event_mutex);
 
        if (ret < 0)
                return ret;

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index c6de3cebc127fe83842887a300cae6d44dcd8c98..a5b614cc3887953946922742a0883819602a9e12 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -320,7 +320,8 @@ void trace_event_enable_cmd_record(bool enable)
        struct trace_event_file *file;
        struct trace_array *tr;
 
-       mutex_lock(&event_mutex);
+       lockdep_assert_held(&event_mutex);
+
        do_for_each_event_file(tr, file) {
 
                if (!(file->flags & EVENT_FILE_FL_ENABLED))
@@ -334,7 +335,6 @@ void trace_event_enable_cmd_record(bool enable)
                        clear_bit(EVENT_FILE_FL_RECORDED_CMD_BIT, &file->flags);
                }
        } while_for_each_event_file();
-       mutex_unlock(&event_mutex);
 }
 
 void trace_event_enable_tgid_record(bool enable)
@@ -342,7 +342,8 @@ void trace_event_enable_tgid_record(bool enable)
        struct trace_event_file *file;
        struct trace_array *tr;
 
-       mutex_lock(&event_mutex);
+       lockdep_assert_held(&event_mutex);
+
        do_for_each_event_file(tr, file) {
                if (!(file->flags & EVENT_FILE_FL_ENABLED))
                        continue;
@@ -356,7 +357,6 @@ void trace_event_enable_tgid_record(bool enable)
                                  &file->flags);
                }
        } while_for_each_event_file();
-       mutex_unlock(&event_mutex);
 }
 
 static int __ftrace_event_enable_disable(struct trace_event_file *file,