linux-kernel - [for-next][PATCH 6/8] ftrace: Prevent RCU stall on PREEMPT

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Date:   Wed, 14 Dec 2022 09:01:39 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Subject: [for-next][PATCH 6/8] ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY kernels

From: "gpiccoli@...lia.com" <gpiccoli@...lia.com>

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@igalia.com

Cc: Mark Rutland <mark.rutland@....com>
Suggested-by: Steven Rostedt <rostedt@...dmis.org>
Acked-by: Paul E. McKenney <paulmck@...nel.org> # from RCU CPU stall warning perspective
Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 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