[PATCH 4.14 40/74] tracing: Fix lock inversion in trace_event_enable_tgid_record()

Greg Kroah-Hartman
2020-01-07T21:13:56Z

From: Prateek Sood <prsood@codeaurora.org>

commit 3a53acf1d9bea11b57c1f6205e3fe73f9d8a3688 upstream.

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: d914ba37d7145 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/trace/trace.c | 8 ++++++++
kernel/trace/trace_events.c | 8 ++++----
2 files changed, 12 insertions(+), 4 deletions(-)

--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4368,6 +4368,10 @@ int trace_keep_overwrite(struct tracer *

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;
@@ -4433,6 +4437,7 @@ static int trace_set_options(struct trac
cmp += 2;
}

+ mutex_lock(&event_mutex);
mutex_lock(&trace_types_lock);

for (i = 0; trace_options[i]; i++) {
@@ -4447,6 +4452,7 @@ static int trace_set_options(struct trac
ret = set_tracer_option(tr, cmp, neg);

mutex_unlock(&trace_types_lock);
+ mutex_unlock(&event_mutex);

/*
* If the first trailing whitespace is replaced with '\0' by strstrip,
@@ -7373,9 +7379,11 @@ trace_options_core_write(struct file *fi
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;
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -326,7 +326,8 @@ void trace_event_enable_cmd_record(bool
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))
@@ -340,7 +341,6 @@ void trace_event_enable_cmd_record(bool
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)
@@ -348,7 +348,8 @@ void trace_event_enable_tgid_record(bool
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;
@@ -362,7 +363,6 @@ void trace_event_enable_tgid_record(bool
&file->flags);
}
} while_for_each_event_file();
- mutex_unlock(&event_mutex);
}

static int __ftrace_event_enable_disable(struct trace_event_file *file,