linux-kernel - [PATCH AUTOSEL 4.14 12/20] printk: use atomic updates for klogd work

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Message-Id: <20220330115336.1672930-12-sashal@kernel.org>
Date:   Wed, 30 Mar 2022 07:53:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     John Ogness <john.ogness@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sasha Levin <sashal@...nel.org>, senozhatsky@...omium.org,
        gregkh@...uxfoundation.org, linux@...ck-us.net,
        stephen.s.brennan@...cle.com
Subject: [PATCH AUTOSEL 4.14 12/20] printk: use atomic updates for klogd work

From: John Ogness <john.ogness@...utronix.de>

[ Upstream commit 2ba3673d70178bf07fb75ff25c54bc478add4021 ]

The per-cpu @printk_pending variable can be updated from
sleepable contexts, such as:

  get_random_bytes()
    warn_unseeded_randomness()
      printk_deferred()
        defer_console_output()

and can be updated from interrupt contexts, such as:

  handle_irq_event_percpu()
    __irq_wake_thread()
      wake_up_process()
        try_to_wake_up()
          select_task_rq()
            select_fallback_rq()
              printk_deferred()
                defer_console_output()

and can be updated from NMI contexts, such as:

  vprintk()
    if (in_nmi()) defer_console_output()

Therefore the atomic variant of the updating functions must be used.

Replace __this_cpu_xchg() with this_cpu_xchg().
Replace __this_cpu_or() with this_cpu_or().

Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: Petr Mladek <pmladek@...e.com>
Link: https://lore.kernel.org/r/87iltld4ue.fsf@jogness.linutronix.de
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/printk/printk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1d7325f09004..8ec99b643a5a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2874,7 +2874,7 @@ static DEFINE_PER_CPU(int, printk_pending);
 
 static void wake_up_klogd_work_func(struct irq_work *irq_work)
 {
-	int pending = __this_cpu_xchg(printk_pending, 0);
+	int pending = this_cpu_xchg(printk_pending, 0);
 
 	if (pending & PRINTK_PENDING_OUTPUT) {
 		/* If trylock fails, someone else is doing the printing */
@@ -2904,7 +2904,7 @@ void wake_up_klogd(void)
 void defer_console_output(void)
 {
 	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();
 }
-- 
2.34.1