Merge branch 'rework/preempt-legacy-kthread' into for-linus

Author: pmladek

kernel/printk/printk.c

@@ -3134,104 +3134,147 @@ static inline void printk_kthreads_check_locked(void) { }
 
 #endif /* CONFIG_PRINTK */
 
+
 /*
- * Print out all remaining records to all consoles.
+ * Print out one record for each console.
  *
  * @do_cond_resched is set by the caller. It can be true only in schedulable
  * context.
  *
  * @next_seq is set to the sequence number after the last available record.
- * The value is valid only when this function returns true. It means that all
- * usable consoles are completely flushed.
+ * The value is valid only when all usable consoles were flushed. It is
+ * when the function returns true (can do the job) and @try_again parameter
+ * is set to false, see below.
  *
  * @handover will be set to true if a printk waiter has taken over the
  * console_lock, in which case the caller is no longer holding the
  * console_lock. Otherwise it is set to false.
  *
- * Returns true when there was at least one usable console and all messages
- * were flushed to all usable consoles. A returned false informs the caller
- * that everything was not flushed (either there were no usable consoles or
- * another context has taken over printing or it is a panic situation and this
- * is not the panic CPU). Regardless the reason, the caller should assume it
- * is not useful to immediately try again.
+ * @try_again will be set to true when it still makes sense to call this
+ * function again. The function could do the job, see the return value.
+ * And some consoles still make progress.
+ *
+ * Returns true when the function could do the job. Some consoles are usable,
+ * and there was no takeover and no panic_on_other_cpu().
  *
  * Requires the console_lock.
  */
-static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
+static bool console_flush_one_record(bool do_cond_resched, u64 *next_seq, bool *handover,
+				     bool *try_again)
 {
 	struct console_flush_type ft;
 	bool any_usable = false;
 	struct console *con;
-	bool any_progress;
 	int cookie;
 
-	*next_seq = 0;
-	*handover = false;
+	*try_again = false;
 
-	do {
-		any_progress = false;
+	printk_get_console_flush_type(&ft);
 
-		printk_get_console_flush_type(&ft);
+	cookie = console_srcu_read_lock();
+	for_each_console_srcu(con) {
+		short flags = console_srcu_read_flags(con);
+		u64 printk_seq;
+		bool progress;
 
-		cookie = console_srcu_read_lock();
-		for_each_console_srcu(con) {
-			short flags = console_srcu_read_flags(con);
-			u64 printk_seq;
-			bool progress;
+		/*
+		 * console_flush_one_record() is only responsible for
+		 * nbcon consoles when the nbcon consoles cannot print via
+		 * their atomic or threaded flushing.
+		 */
+		if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
+			continue;
 
-			/*
-			 * console_flush_all() is only responsible for nbcon
-			 * consoles when the nbcon consoles cannot print via
-			 * their atomic or threaded flushing.
-			 */
-			if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
-				continue;
+		if (!console_is_usable(con, flags, !do_cond_resched))
+			continue;
+		any_usable = true;
 
-			if (!console_is_usable(con, flags, !do_cond_resched))
-				continue;
-			any_usable = true;
+		if (flags & CON_NBCON) {
+			progress = nbcon_legacy_emit_next_record(con, handover, cookie,
+								 !do_cond_resched);
+			printk_seq = nbcon_seq_read(con);
+		} else {
+			progress = console_emit_next_record(con, handover, cookie);
+			printk_seq = con->seq;
+		}
 
-			if (flags & CON_NBCON) {
-				progress = nbcon_legacy_emit_next_record(con, handover, cookie,
-									 !do_cond_resched);
-				printk_seq = nbcon_seq_read(con);
-			} else {
-				progress = console_emit_next_record(con, handover, cookie);
-				printk_seq = con->seq;
-			}
+		/*
+		 * If a handover has occurred, the SRCU read lock
+		 * is already released.
+		 */
+		if (*handover)
+			goto fail;
 
-			/*
-			 * If a handover has occurred, the SRCU read lock
-			 * is already released.
-			 */
-			if (*handover)
-				return false;
+		/* Track the next of the highest seq flushed. */
+		if (printk_seq > *next_seq)
+			*next_seq = printk_seq;
 
-			/* Track the next of the highest seq flushed. */
-			if (printk_seq > *next_seq)
-				*next_seq = printk_seq;
+		if (!progress)
+			continue;
 
-			if (!progress)
-				continue;
-			any_progress = true;
+		/*
+		 * An usable console made a progress. There might still be
+		 * pending messages.
+		 */
+		*try_again = true;
 
-			/* Allow panic_cpu to take over the consoles safely. */
-			if (panic_on_other_cpu())
-				goto abandon;
+		/* Allow panic_cpu to take over the consoles safely. */
+		if (panic_on_other_cpu())
+			goto fail_srcu;
 
-			if (do_cond_resched)
-				cond_resched();
-		}
-		console_srcu_read_unlock(cookie);
-	} while (any_progress);
+		if (do_cond_resched)
+			cond_resched();
+	}
+	console_srcu_read_unlock(cookie);
 
 	return any_usable;
 
-abandon:
+fail_srcu:
 	console_srcu_read_unlock(cookie);
+fail:
+	*try_again = false;
 	return false;
 }
 
+/*
+ * Print out all remaining records to all consoles.
+ *
+ * @do_cond_resched is set by the caller. It can be true only in schedulable
+ * context.
+ *
+ * @next_seq is set to the sequence number after the last available record.
+ * The value is valid only when this function returns true. It means that all
+ * usable consoles are completely flushed.
+ *
+ * @handover will be set to true if a printk waiter has taken over the
+ * console_lock, in which case the caller is no longer holding the
+ * console_lock. Otherwise it is set to false.
+ *
+ * Returns true when there was at least one usable console and all messages
+ * were flushed to all usable consoles. A returned false informs the caller
+ * that everything was not flushed (either there were no usable consoles or
+ * another context has taken over printing or it is a panic situation and this
+ * is not the panic CPU). Regardless the reason, the caller should assume it
+ * is not useful to immediately try again.
+ *
+ * Requires the console_lock.
+ */
+static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
+{
+	bool try_again;
+	bool ret;
+
+	*next_seq = 0;
+	*handover = false;
+
+	do {
+		ret = console_flush_one_record(do_cond_resched, next_seq,
+					       handover, &try_again);
+	} while (try_again);
+
+	return ret;
+}
+
 static void __console_flush_and_unlock(void)
 {
 	bool do_cond_resched;
@@ -3597,17 +3640,26 @@ static bool legacy_kthread_should_wakeup(void)
 
 static int legacy_kthread_func(void *unused)
 {
-	for (;;) {
-		wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup());
+	bool try_again;
+
+wait_for_event:
+	wait_event_interruptible(legacy_wait, legacy_kthread_should_wakeup());
+
+	do {
+		bool handover = false;
+		u64 next_seq = 0;
 
 		if (kthread_should_stop())
-			break;
+			return 0;
 
 		console_lock();
-		__console_flush_and_unlock();
-	}
+		console_flush_one_record(true, &next_seq, &handover, &try_again);
+		if (!handover)
+			__console_unlock();
 
-	return 0;
+	} while (try_again);
+
+	goto wait_for_event;
 }
 
 static bool legacy_kthread_create(void)