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SubjectRe: [PATCH] trace: circular dependency for trace_types_lock and event_mutex

Hi Prateek,

Thanks for the patch. Note, I think a better subject is:

tracing: Fix lock inversion caused by trace_event_enable_tgid_record()


On Tue, 3 Dec 2019 16:03:32 +0000
Prateek Sood <prsood@codeaurora.org> wrote:

> 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

What's this Change-Id? Something internal?

I'll be adding:

Link: http://lkml.kernel.org/r/0101016ecc80a1fa-27cc3e87-c16d-4cd6-b3c6-9c893010fdef-000000@us-west-2.amazonses.com

I'll test this out, and probably even add a stable tag.

-- Steve



> 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;
> }

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