Commit 54a16ff6 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

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: b9b0c831 ("ftrace: Convert graph filter to use hash tables")
Reported-by: default avatar"Paul E. McKenney" <paulmck@kernel.org>
Reviewed-by: default avatarJoel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 16052dd5

kernel/trace/ftrace.c

+9 −2
Original line number Diff line number Diff line
@@ -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);

	}

kernel/trace/trace.h

+2 −0
Original line number Diff line number Diff line
@@ -979,6 +979,7 @@ 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());
@@ -1031,6 +1032,7 @@ 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());

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