[PATCH] ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY kernels

[Guilherme G. Piccoli]

The function match_records() may take a while due to a large
number of string comparisons, so when in PREEMPT_VOLUNTARY
kernels we could face RCU stalls due to that.

Add a cond_resched() to prevent that.

Link: https://lkml.kernel.org/r/20221115204847.593616-1-gpiccoli@xxxxxxxxxx

Cc: Mark Rutland <mark.rutland@xxxxxxx>
Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx> # from RCU CPU stall warning perspective
Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx>
Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/ftrace.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index d04552c0c275..b8e374a372e5 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -4204,6 +4204,7 @@ match_records(struct ftrace_hash *hash, char *func, int len, char *mod)
 			}
 			found = 1;
 		}
+		cond_resched();
 	} while_for_each_ftrace_rec();
  out_unlock:
 	mutex_unlock(&ftrace_lock);
-- 
2.35.1