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printk: wake waiters for safe and NMI contexts

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When printk() is called from safe or NMI contexts, it will directly
store the record (vprintk_store()) and then defer the console output.
However, defer_console_output() only causes console printing and does
not wake any waiters of new records.

Wake waiters from defer_console_output() so that they also are aware
of the new records from safe and NMI contexts.

Fixes: 03fc7f9c99 ("printk/nmi: Prevent deadlock when accessing the main log buffer in NMI")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220421212250.565456-6-john.ogness@linutronix.de
This commit is contained in:
John Ogness 2022-04-21 23:28:40 +02:06 committed by Petr Mladek
parent 938ba4084a
commit 5341b93dea
1 changed files with 16 additions and 12 deletions
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28
kernel/printk/printk.c
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@ -754,7 +754,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
* prepare_to_wait_event() pairs with the full memory barrier
* within wq_has_sleeper().
*
* This pairs with wake_up_klogd:A.
* This pairs with __wake_up_klogd:A.
*/
ret = wait_event_interruptible(log_wait,
prb_read_valid(prb,
@ -1532,7 +1532,7 @@ static int syslog_print(char __user *buf, int size)
* prepare_to_wait_event() pairs with the full memory barrier
* within wq_has_sleeper().
*
* This pairs with wake_up_klogd:A.
* This pairs with __wake_up_klogd:A.
*/
len = wait_event_interruptible(log_wait,
prb_read_valid(prb, seq, NULL)); /* LMM(syslog_print:A) */
@ -3332,7 +3332,7 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work)
static DEFINE_PER_CPU(struct irq_work, wake_up_klogd_work) =
IRQ_WORK_INIT_LAZY(wake_up_klogd_work_func);
void wake_up_klogd(void)
static void __wake_up_klogd(int val)
{
if (!printk_percpu_data_ready())
return;
@ -3349,22 +3349,26 @@ void wake_up_klogd(void)
*
* This pairs with devkmsg_read:A and syslog_print:A.
*/
if (wq_has_sleeper(&log_wait)) { /* LMM(wake_up_klogd:A) */
this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
if (wq_has_sleeper(&log_wait) || /* LMM(__wake_up_klogd:A) */
(val & PRINTK_PENDING_OUTPUT)) {
this_cpu_or(printk_pending, val);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
}
preempt_enable();
}
void wake_up_klogd(void)
{
__wake_up_klogd(PRINTK_PENDING_WAKEUP);
}
void defer_console_output(void)
{
if (!printk_percpu_data_ready())
return;
preempt_disable();
this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
/*
* New messages may have been added directly to the ringbuffer
* using vprintk_store(), so wake any waiters as well.
*/
__wake_up_klogd(PRINTK_PENDING_WAKEUP | PRINTK_PENDING_OUTPUT);
}
void printk_trigger_flush(void)