On Tue, 4 Dec 2018 11:12:43 +0000
Will Deacon [off-list ref] wrote:

quoted

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 8ef9fc226037..42e89397778b 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c

@@ -2393,11 +2393,14 @@ void __weak ftrace_replace_code(int enable)
 {
 	struct dyn_ftrace *rec;
 	struct ftrace_page *pg;
+	bool schedulable;
 	int failed;
 
 	if (unlikely(ftrace_disabled))
 		return;
 
+	schedulable = !irqs_disabled() & !preempt_count();  

Looks suspiciously like a bitwise preemptible() to me!

Ah, thanks. Yeah, that should have been &&. But what did you expect.
I didn't even compile this ;-)

quoted

+
 	do_for_each_ftrace_rec(pg, rec) {
 
 		if (rec->flags & FTRACE_FL_DISABLED)

@@ -2409,6 +2412,8 @@ void __weak ftrace_replace_code(int enable)
 			/* Stop processing */
 			return;
 		}
+		if (schedulable)
+			cond_resched();
 	} while_for_each_ftrace_rec();
 }  

If this solves the problem in core code, them I'm all for it. Otherwise, I
was thinking of rolling our own ftrace_replace_code() for arm64, but that's
going to involve a fair amount of duplication.

If it does, then I'll add it. Or take a patch for it ;-) 

My main concern is that this can be called from non schedulable context.

-- Steve

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