diff options
| author | Frederic Weisbecker <fweisbec@gmail.com> | 2008-10-31 13:08:28 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2008-11-04 17:14:04 +0100 |
| commit | 07695fa04e8a3384b0c855398ce1f7885bd7dc3b (patch) | |
| tree | 5a70702087ea1f603b69281aaa270b117f37a63f | |
| parent | 71566a0d161edec70361b7f90f6e54af6a6d5d05 (diff) | |
tracing/ftrace: fix a race condition in sched_switch tracer
Impact: fix race condition in sched_switch tracer
This patch fixes a race condition in the sched_switch tracer. If
several tasks (IE: concurrent initcalls) are playing with
tracing_start_cmdline_record() and tracing_stop_cmdline_record(), the
following situation could happen:
_ Task A and B are using the same tracepoint probe. Task A holds it.
Task B is sleeping and doesn't hold it.
_ Task A frees the sched tracer, then sched_ref is decremented to 0.
_ Task A is preempted and hadn't yet unregistered its tracepoint
probe, then B runs.
_ B increments sched_ref, sees it's 1 and then guess it has to
register its probe. But it has not been freed by task A.
_ A lot of bad things can happen after that...
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
| -rw-r--r-- | kernel/trace/trace_sched_switch.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c index b8f56beb1a6..59de5141207 100644 --- a/kernel/trace/trace_sched_switch.c +++ b/kernel/trace/trace_sched_switch.c @@ -17,6 +17,7 @@ static struct trace_array *ctx_trace; static int __read_mostly tracer_enabled; static atomic_t sched_ref; +static DEFINE_MUTEX(tracepoint_mutex); static void probe_sched_switch(struct rq *__rq, struct task_struct *prev, @@ -125,18 +126,22 @@ static void tracing_start_sched_switch(void) { long ref; + mutex_lock(&tracepoint_mutex); ref = atomic_inc_return(&sched_ref); if (ref == 1) tracing_sched_register(); + mutex_unlock(&tracepoint_mutex); } static void tracing_stop_sched_switch(void) { long ref; + mutex_lock(&tracepoint_mutex); ref = atomic_dec_and_test(&sched_ref); if (ref) tracing_sched_unregister(); + mutex_unlock(&tracepoint_mutex); } void tracing_start_cmdline_record(void) |