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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2020-02-05 17:20:32 +0300
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2020-02-06 01:16:42 +0300
commit54a16ff6f2e50775145b210bcd94d62c3c2af117 (patch)
tree9fcea20433e1f5c27406e9a793e6bd4d090dd03c /kernel/trace/ftrace.c
parent16052dd5bdfa16dbe18d8c1d4cde2ddab9d23177 (diff)
downloadlinux-54a16ff6f2e50775145b210bcd94d62c3c2af117.tar.xz
ftrace: Protect ftrace_graph_hash with ftrace_sync
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>
Diffstat (limited to 'kernel/trace/ftrace.c')
-rw-r--r--kernel/trace/ftrace.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 481ede3eac13..3f7ee102868a 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5867,8 +5867,15 @@ ftrace_graph_release(struct inode *inode, struct file *file)
mutex_unlock(&graph_lock);
- /* Wait till all users are no longer using the old hash */
- synchronize_rcu();
+ /*
+ * 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);
}