Commit 2ba3673d authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: use atomic updates for klogd work 



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: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/87iltld4ue.fsf@jogness.linutronix.de
parent a2293277

kernel/printk/printk.c

+2 −2
Original line number Diff line number Diff line
@@ -3226,7 +3226,7 @@ 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 */
@@ -3260,7 +3260,7 @@ 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();

}