From: Steven Rostedt <rostedt@goodmis.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-rt-users <linux-rt-users@vger.kernel.org>,
Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: [PATCH RT] printk: Shortcut out of waiter spinning on PREEMPT_RT
Date: Tue, 15 Jan 2019 12:39:10 -0500 [thread overview]
Message-ID: <20190115123910.2b18df54@gandalf.local.home> (raw)
From: Steven Rostedt (VMware) <rostedt@goodmis.org>
As the consoles are written with preemption enabled in PREEMPT_RT, we
must not have any task spinning waiting on them. Currently, the code
that would make the task spin is #ifdef out when PREEMPT_RT is
enabled, but why go through grabbing of the locks to see if an owner is
set, when it never will be?
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a43d07d4e043..1a61132deec1 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1742,6 +1742,13 @@ static int console_trylock_spinning(void)
if (console_trylock())
return 1;
+ /*
+ * The consoles are preemptable in PREEMPT_RT, which can cause
+ * spinning to deadlock.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT_RT_FULL))
+ return 0;
+
printk_safe_enter_irqsave(flags);
raw_spin_lock(&console_owner_lock);
next reply other threads:[~2019-01-15 17:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-15 17:39 Steven Rostedt [this message]
2019-01-15 18:54 ` [PATCH RT] printk: Shortcut out of waiter spinning on PREEMPT_RT Sebastian Andrzej Siewior
2019-01-15 19:58 ` Steven Rostedt
2019-01-16 10:07 ` Petr Mladek
2019-01-16 11:43 ` Sergey Senozhatsky
2019-01-16 12:27 ` Steven Rostedt
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