The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 54a16ff6f2e50775145b210bcd94d62c3c2af117 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> Date: Wed, 5 Feb 2020 09:20:32 -0500 Subject: [PATCH] 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@xxxxxxxxxxxxxxx Fixes: b9b0c831bed26 ("ftrace: Convert graph filter to use hash tables") Reported-by: "Paul E. McKenney" <paulmck@xxxxxxxxxx> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> 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); } diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index 8c52f5de9384..3c75d29bd861 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -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());
