linux-kernel - [PATCH 5.15-rt] printk: ignore that console preempted by irq/softirq.

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Date: Thu, 23 May 2024 23:54:01 +0800 (CST)
From: <xu.xin16@....com.cn>
To: <bigeasy@...utronix.de>, <john.ogness@...utronix.de>,
        <rostedt@...dmis.org>
Cc: <zhang.yunkai@....com.cn>, <yang.yang29@....com.cn>,
        <liu.chun2@....com.cn>, <si.hao@....com.cn>,
        <linux-kernel@...r.kernel.org>, <linux-rt-users@...r.kernel.org>,
        <rostedt@...dmis.org>
Subject:  [PATCH  5.15-rt] printk: ignore that console preempted by irq/softirq.

From: xu xin <xu.xin16@....com.cn>

When we're in the unpreemptible context on the same cpu with which the
thread of console locates on, we should ignore this console for
pr_flush, because it's a vain and always lead to timeout  until the console
thread get cpu resource.

Fixes: e65be5f4dc3ed("printk: Update John Ogness' printk series")
Signed-off-by: xu xin <xu.xin16@....com.cn>
Cc: Zhang Yunkai <zhang.yunkai@....com.cn>
---
 kernel/printk/printk.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7f27cfee283e..faab85dd4439 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3735,6 +3735,14 @@ bool pr_flush(int timeout_ms, bool reset_on_progress)
 		diff = 0;

 		for_each_console(con) {
+			/*
+			 * When we're in the unpreemptible context on the same cpu
+			 * with which the thread of console locates on, we should
+			 * ignore this console, because it's a vain.
+			 */
+			if (!preemptible() && con->thread &&
+					task_cpu(con->thread) == smp_processor_id())
+				continue;
 			if (!(con->flags & CON_ENABLED))
 				continue;
 			printk_seq = read_console_seq(con);
-- 
2.15.2