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Subject[PATCH] trace: circular dependency for trace_types_lock and event_mutex
Date
       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.

Change-Id: I3752a77c59555852c2241f7775ec4a1960c15c15
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
---
kernel/trace/trace.c | 6 ++++++
kernel/trace/trace_events.c | 8 ++++----
kernel/trace/trace_irqsoff.c | 4 ++++
kernel/trace/trace_sched_wakeup.c | 4 ++++
4 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 6a0ee91..2c09aa1 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4590,6 +4590,8 @@ int trace_keep_overwrite(struct tracer *tracer, u32 mask, int set)

int set_tracer_flag(struct trace_array *tr, unsigned int mask, int enabled)
{
+ lockdep_assert_held(&event_mutex);
+
/* do nothing if flag is already set */
if (!!(tr->trace_flags & mask) == !!enabled)
return 0;
@@ -4657,6 +4659,7 @@ 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);
@@ -4667,6 +4670,7 @@ 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,
@@ -7972,9 +7976,11 @@ static void get_tr_index(void *data, struct trace_array **ptr,
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 fba87d1..995061b 100644
--- 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,
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index a745b0c..887cdb5 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -560,8 +560,10 @@ static int __irqsoff_tracer_init(struct trace_array *tr)
save_flags = tr->trace_flags;

/* non overwrite screws up the latency tracers */
+ mutex_lock(&event_mutex);
set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);
+ mutex_unlock(&event_mutex);

tr->max_latency = 0;
irqsoff_trace = tr;
@@ -586,8 +588,10 @@ static void __irqsoff_tracer_reset(struct trace_array *tr)

stop_irqsoff_tracer(tr, is_graph(tr));

+ mutex_lock(&event_mutex);
set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
+ mutex_unlock(&event_mutex);
ftrace_reset_array_ops(tr);

irqsoff_busy = false;
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 5e43b96..0bc67d1 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -671,8 +671,10 @@ static int __wakeup_tracer_init(struct trace_array *tr)
save_flags = tr->trace_flags;

/* non overwrite screws up the latency tracers */
+ mutex_lock(&event_mutex);
set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);
+ mutex_unlock(&event_mutex);

tr->max_latency = 0;
wakeup_trace = tr;
@@ -722,8 +724,10 @@ static void wakeup_tracer_reset(struct trace_array *tr)
/* make sure we put back any tasks we are tracing */
wakeup_reset(tr);

+ mutex_lock(&event_mutex);
set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
+ mutex_unlock(&event_mutex);
ftrace_reset_array_ops(tr);
wakeup_busy = false;
}
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.,
is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
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