linux-kernel - RE: [PREEMPT_RT][PATCH] printk: Enhance the condition check of msleep in pr

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Message-ID: <87eeb8w08q.fsf@jogness.linutronix.de>
Date:   Thu, 05 Aug 2021 14:27:25 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     "Qin\, Chao" <chao.qin@...el.com>, Joe Perches <joe@...ches.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rt-users\@vger.kernel.org" <linux-rt-users@...r.kernel.org>,
        "bigeasy\@linutronix.de" <bigeasy@...utronix.de>,
        "tglx\@linutronix.de" <tglx@...utronix.de>,
        "mgross\@linux.intel.com" <mgross@...ux.intel.com>,
        "Mei\, Paul" <paul.mei@...el.com>, "Li\, Lili" <lili.li@...el.com>,
        "Qin\, Chao" <chao.qin@...el.com>
Subject: RE: [PREEMPT_RT][PATCH] printk: Enhance the condition check of msleep in pr_flush()

Hello Steven,

Could you please cherry-pick 83e9288d9c42("printk: Enhance the condition
check of msleep in pr_flush()") from linux-rt-devel.git (branch
linux-5.14.y-rt-rebase) for the next stable v5.10-rt release?

The commit is provided below as well.

Thanks.

John Ogness

On 2021-08-05, "Qin, Chao" <chao.qin@...el.com> wrote:
> Do you have plan to backport this fix into v5.10.y-rt kernel?


>From 83e9288d9c4295d1195e9d780fcbc42c72ba4a83 Mon Sep 17 00:00:00 2001
From: Chao Qin <chao.qin@...el.com>
Date: Mon, 19 Jul 2021 10:26:50 +0800
Subject: [PATCH] printk: Enhance the condition check of msleep in pr_flush()

There is msleep in pr_flush(). If call WARN() in the early boot
stage such as in early_initcall, pr_flush() will run into msleep
when process scheduler is not ready yet. And then the system will
sleep forever.

Before the system_state is SYSTEM_RUNNING, make sure DO NOT sleep
in pr_flush().

Fixes: c0b395bd0fe3("printk: add pr_flush()")
Signed-off-by: Chao Qin <chao.qin@...el.com>
Signed-off-by: Lili Li <lili.li@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/lkml/20210719022649.3444072-1-chao.qin@intel.com
---
 kernel/printk/printk.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e4085e2cafb5..500ae4b18864 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3661,7 +3661,9 @@ bool pr_flush(int timeout_ms, bool reset_on_progress)
 	u64 diff;
 	u64 seq;
 
-	may_sleep = (preemptible() && !in_softirq());
+	may_sleep = (preemptible() &&
+		     !in_softirq() &&
+		     system_state >= SYSTEM_RUNNING);
 
 	seq = prb_next_seq(prb);
 
-- 
2.20.1