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SubjectRe: [for-next][PATCH 6/8] ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY kernels
On Wed, 14 Dec 2022 11:15:44 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 14 Dec 2022 12:53:04 -0300
> "Guilherme G. Piccoli" <gpiccoli@igalia.com> wrote:
>
> > On 14/12/2022 11:01, Steven Rostedt wrote:
> > > From: "gpiccoli@igalia.com" <gpiccoli@igalia.com>
> >
> > Hi Steve, would be possible to use my full name here, like: Guilherme G.
> > Piccoli <gpiccoli@igalia.com> ?
>
> Sure, I haven't pushed to the next repo yet.
>
> I found the reason it didn't go into my patchwork, and did a resend via a
> "redirect", and that must have changed the from address :-/
>

Here's the new update:

-- Steve


From d0b24b4e91fcb8408c4979888547f86be514e337 Mon Sep 17 00:00:00 2001
From: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Date: Tue, 15 Nov 2022 17:48:47 -0300
Subject: [PATCH] ftrace: Prevent RCU stall on PREEMPT_VOLUNTARY kernels

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@arm.com>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org> # from RCU CPU stall warning perspective
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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
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