linux-kernel - [PATCH] printk: defer_console_output: do not assume interrupts disabled

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Message-Id: <20220203112915.1350753-1-john.ogness@linutronix.de>
Date:   Thu,  3 Feb 2022 12:35:15 +0106
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH] printk: defer_console_output: do not assume interrupts disabled

With commit 458df9fd4815 ("printk: remove separate printk_sched
buffers and use printk buf instead") defer_console_output() was
changed to no longer disable interrupts. However, it used the
function __this_cpu_or(), which assumes interrupts disabled. That
also should have been changed to this_cpu_or().

Although defer_console_output() is mostly used when interrupts are
disabled, this is not always the case. One example is
get_random_bytes(), which is often called with interrupts enabled.

  get_random_bytes()
    warn_unseeded_randomness()
      printk_deferred()

Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
---
 kernel/printk/printk.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82abfaf3c2aa..164ccdb9423e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3262,7 +3262,7 @@ void defer_console_output(void)
 		return;
 
 	preempt_disable();
-	__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+	this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
 	irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
 	preempt_enable();
 }

base-commit: 88808fbbead481aedb46640a5ace69c58287f56a
-- 
2.30.2