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FAILED: patch "[PATCH] ftrace: Protect ftrace_graph_hash with ftrace_sync" failed to apply to 4.19-stable tree

PATCH [email protected] 1 participant 1 message Feb 7, 2020

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The patch below does not apply to the 4.19-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 <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 54a16ff6f2e50775145b210bcd94d62c3c2af117 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (VMware)" <[email protected]>
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 open here
Cc [email protected]
Fixes b9b0c831bed26 ("ftrace: Convert graph filter to use hash tables")
Reported-by "Paul E. McKenney" <[email protected]>
Reviewed-by Joel Fernandes (Google) <[email protected]>
Signed-off-by Steven Rostedt (VMware) <[email protected]>
kernel/trace/ftrace.c +9 -2
index 481ede3eac13..3f7ee102868a 100644
@@ -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
index 8c52f5de9384..3c75d29bd861 100644
@@ -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());