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authorFrederic Weisbecker <fweisbec@gmail.com>2008-10-31 13:08:28 +0100
committerIngo Molnar <mingo@elte.hu>2008-11-04 17:14:04 +0100
commit07695fa04e8a3384b0c855398ce1f7885bd7dc3b (patch)
tree5a70702087ea1f603b69281aaa270b117f37a63f /kernel/trace/trace_sched_switch.c
parent71566a0d161edec70361b7f90f6e54af6a6d5d05 (diff)
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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>
Diffstat (limited to 'kernel/trace/trace_sched_switch.c')
-rw-r--r--kernel/trace/trace_sched_switch.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index b8f56be..59de514 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)