From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Date: Wed, 5 Feb 2020 09:20:32 -0500
Subject: ftrace: Protect ftrace_graph_hash with ftrace_sync
Git-commit: 54a16ff6f2e50775145b210bcd94d62c3c2af117
Patch-mainline: v5.6-rc1
References: git-fixes
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>
Acked-by: Miroslav Benes <mbenes@suse.cz>
---
kernel/trace/ftrace.c | 11 +++++++++--
kernel/trace/trace.h | 2 ++
2 files changed, 11 insertions(+), 2 deletions(-)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5079,8 +5079,15 @@ ftrace_graph_release(struct inode *inode
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);
}
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -825,6 +825,7 @@ static inline int ftrace_graph_addr(unsi
* 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());
@@ -862,6 +863,7 @@ static inline int ftrace_graph_notrace_a
* 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());