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From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 20 Apr 2022 01:52:27 +0206
Subject: [PATCH 05/18] printk: wake waiters for safe and NMI contexts
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>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20220419234637.357112-6-john.ogness@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -754,7 +754,7 @@ static ssize_t devkmsg_read(struct file
* 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
* 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(stru
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 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)
|
