From: "Steven Rostedt (VMware)" rostedt@goodmis.org
[ Upstream commit 54a16ff6f2e50775145b210bcd94d62c3c2af117 ]
As function_graph tracer can run when RCU is not "watching", it can not be protected by synchronize_rcu() it requires running a task on each CPU before it can be freed. Calling schedule_on_each_cpu(ftrace_sync) needs to be used.
Link: https://lore.kernel.org/r/20200205131110.GT2935@paulmck-ThinkPad-P72
Cc: stable@vger.kernel.org Fixes: b9b0c831bed26 ("ftrace: Convert graph filter to use hash tables") Reported-by: "Paul E. McKenney" paulmck@kernel.org Reviewed-by: Joel Fernandes (Google) joel@joelfernandes.org Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- kernel/trace/ftrace.c | 11 +++++++++-- kernel/trace/trace.h | 2 ++ 2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 09c69ad..5379523 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5344,8 +5344,15 @@ static int g_show(struct seq_file *m, void *v)
mutex_unlock(&graph_lock);
- /* Wait till all users are no longer using the old hash */ - synchronize_sched(); + /* + * We need to do a hard force of sched synchronization. + * This is because we use preempt_disable() to do RCU, but + * the function tracers can be called where RCU is not watching + * (like before user_exit()). We can not rely on the RCU + * infrastructure to do the synchronization, thus we must do it + * ourselves. + */ + schedule_on_each_cpu(ftrace_sync);
free_ftrace_hash(old_hash); } diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 8894ecd..1791c10 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -885,6 +885,7 @@ static inline int ftrace_graph_addr(struct ftrace_graph_ent *trace) * Have to open code "rcu_dereference_sched()" because the * function graph tracer can be called when RCU is not * "watching". + * Protected with schedule_on_each_cpu(ftrace_sync) */ hash = rcu_dereference_protected(ftrace_graph_hash, !preemptible());
@@ -937,6 +938,7 @@ static inline int ftrace_graph_notrace_addr(unsigned long addr) * Have to open code "rcu_dereference_sched()" because the * function graph tracer can be called when RCU is not * "watching". + * Protected with schedule_on_each_cpu(ftrace_sync) */ notrace_hash = rcu_dereference_protected(ftrace_graph_notrace_hash, !preemptible());