From: John Ogness john.ogness@linutronix.de
[ Upstream commit 5341b93dea8c39d7612f7a227015d4b1d5cf30db ]
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: 03fc7f9c99c1 ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/printk/printk.c | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8964b1db2745..4f344e7b2878 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -743,7 +743,7 @@ 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, @@ -1521,7 +1521,7 @@ 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) */ @@ -3267,7 +3267,7 @@ 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; @@ -3284,22 +3284,26 @@ 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 defer_console_output(void) +void wake_up_klogd(void) { - if (!printk_percpu_data_ready()) - return; + __wake_up_klogd(PRINTK_PENDING_WAKEUP); +}
- preempt_disable(); - this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT); - irq_work_queue(this_cpu_ptr(&wake_up_klogd_work)); - preempt_enable(); +void defer_console_output(void) +{ + /* + * 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)