Re: [PATCH] net/skbuff: silence warnings under memory pressure

On (19/11/18 16:27), Petr Mladek wrote:

quoted

quoted

@@ -2027,8 +2027,11 @@ asmlinkage int vprintk_emit(int facility, int level,
 	pending_output = (curr_log_seq != log_next_seq);
 	logbuf_unlock_irqrestore(flags);
 
+	if (!pending_output)
+		return printed_len;
+
 	/* If called from the scheduler, we can not call up(). */
-	if (!in_sched && pending_output) {
+	if (!in_sched) {
 		/*
 		 * Disable preemption to avoid being preempted while holding
 		 * console_sem which would prevent anyone from printing to

@@ -2043,10 +2046,11 @@ asmlinkage int vprintk_emit(int facility, int level,
 		if (console_trylock_spinning())
 			console_unlock();
 		preempt_enable();
-	}
 
-	if (pending_output)
+		wake_up_interruptible(&log_wait);

I do not like this. As a result, normal printk() will always deadlock
in the scheduler code, including WARN() calls. The chance of the
deadlock is small now. It happens only when there is another
process waiting for console_sem.

Why would it *always* deadlock? If this is the case, why we don't *always*
deadlock doing the very same wake_up_process() from console_unlock()?

	-ss