Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk

Pull printk updates from Petr Mladek:

 - There is a situation when early console is not deregistered because
   the preferred one matches a wrong entry. It caused messages to appear
   twice.

   This is the 2nd attempt to fix it. The first one was wrong, see the
   commit c6c7d83b9c9e ('Revert "console: don't prefer first registered
   if DT specifies stdout-path"').

   The fix is coupled with some small code clean up. Well, the console
   registration code would deserve a big one. We need to think about it.

 - Do not lose information about the preemtive context when the console
   semaphore is re-taken.

 - Do not block CPU hotplug when someone else is already pushing
   messages to the console.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
  printk: fix double printing with earlycon
  printk: rename selected_console -> preferred_console
  printk: fix name/type/scope of preferred_console var
  printk: Correctly handle preemption in console_unlock()
  printk: use console_trylock() in console_cpu_notify()

1 files changed, 56 insertions, 25 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2984fb0f0257..779479ac9f57 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -269,8 +269,8 @@ static struct console *exclusive_console;
 #define MAX_CMDLINECONSOLES 8
 
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
+static int console_cmdline_cnt;
 
-static int selected_console = -1;
 static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
@@ -1906,24 +1906,38 @@ static int __add_preferred_console(char *name, int idx, char *options,
 	 *	See if this tty is not yet registered, and
 	 *	if we have a slot free.
 	 */
-	for (i = 0, c = console_cmdline;
-	     i < MAX_CMDLINECONSOLES && c->name[0];
-	     i++, c++) {
+	for (i = 0, c = console_cmdline; i < console_cmdline_cnt; i++, c++) {
 		if (strcmp(c->name, name) == 0 && c->index == idx) {
-			if (!brl_options)
-				selected_console = i;
+			if (brl_options)
+				return 0;
+
+			/*
+			 * Maintain an invariant that will help to find if
+			 * the matching console is preferred, see
+			 * register_console():
+			 *
+			 * The last non-braille console is always
+			 * the preferred one.
+			 */
+			if (i != console_cmdline_cnt - 1)
+				swap(console_cmdline[i],
+				     console_cmdline[console_cmdline_cnt - 1]);
+
+			preferred_console = console_cmdline_cnt - 1;
+
 			return 0;
 		}
 	}
 	if (i == MAX_CMDLINECONSOLES)
 		return -E2BIG;
 	if (!brl_options)
-		selected_console = i;
+		preferred_console = i;
 	strlcpy(c->name, name, sizeof(c->name));
 	c->options = options;
 	braille_set_options(c, brl_options);
 
 	c->index = idx;
+	console_cmdline_cnt++;
 	return 0;
 }
 /*
@@ -2031,15 +2045,16 @@ void resume_console(void)
  * @cpu: unused
  *
  * If printk() is called from a CPU that is not online yet, the messages
- * will be spooled but will not show up on the console.  This function is
- * called when a new CPU comes online (or fails to come up), and ensures
- * that any such output gets printed.
+ * will be printed on the console only if there are CON_ANYTIME consoles.
+ * This function is called when a new CPU comes online (or fails to come
+ * up) or goes offline.
  */
 static int console_cpu_notify(unsigned int cpu)
 {
 	if (!cpuhp_tasks_frozen) {
-		console_lock();
-		console_unlock();
+		/* If trylock fails, someone else is doing the printing */
+		if (console_trylock())
+			console_unlock();
 	}
 	return 0;
 }
@@ -2161,7 +2176,7 @@ void console_unlock(void)
 	}
 
 	/*
-	 * Console drivers are called under logbuf_lock, so
+	 * Console drivers are called with interrupts disabled, so
 	 * @console_may_schedule should be cleared before; however, we may
 	 * end up dumping a lot of lines, for example, if called from
 	 * console registration path, and should invoke cond_resched()
@@ -2169,11 +2184,15 @@ void console_unlock(void)
 	 * scheduling stall on a slow console leading to RCU stall and
 	 * softlockup warnings which exacerbate the issue with more
 	 * messages practically incapacitating the system.
+	 *
+	 * console_trylock() is not able to detect the preemptive
+	 * context reliably. Therefore the value must be stored before
+	 * and cleared after the the "again" goto label.
 	 */
 	do_cond_resched = console_may_schedule;
+again:
 	console_may_schedule = 0;
 
-again:
 	/*
 	 * We released the console_sem lock, so we need to recheck if
 	 * cpu is online and (if not) is there at least one CON_ANYTIME
@@ -2409,6 +2428,7 @@ void register_console(struct console *newcon)
 	unsigned long flags;
 	struct console *bcon = NULL;
 	struct console_cmdline *c;
+	static bool has_preferred;
 
 	if (console_drivers)
 		for_each_console(bcon)
@@ -2435,15 +2455,15 @@ void register_console(struct console *newcon)
 	if (console_drivers && console_drivers->flags & CON_BOOT)
 		bcon = console_drivers;
 
-	if (preferred_console < 0 || bcon || !console_drivers)
-		preferred_console = selected_console;
+	if (!has_preferred || bcon || !console_drivers)
+		has_preferred = preferred_console >= 0;
 
 	/*
 	 *	See if we want to use this console driver. If we
 	 *	didn't select a console we take the first one
 	 *	that registers here.
 	 */
-	if (preferred_console < 0) {
+	if (!has_preferred) {
 		if (newcon->index < 0)
 			newcon->index = 0;
 		if (newcon->setup == NULL ||
@@ -2451,18 +2471,29 @@ void register_console(struct console *newcon)
 			newcon->flags |= CON_ENABLED;
 			if (newcon->device) {
 				newcon->flags |= CON_CONSDEV;
-				preferred_console = 0;
+				has_preferred = true;
 			}
 		}
 	}
 
 	/*
-	 *	See if this console matches one we selected on
-	 *	the command line.
+	 * See if this console matches one we selected on the command line.
+	 *
+	 * There may be several entries in the console_cmdline array matching
+	 * with the same console, one with newcon->match(), another by
+	 * name/index:
+	 *
+	 *	pl011,mmio,0x87e024000000,115200 -- added from SPCR
+	 *	ttyAMA0 -- added from command line
+	 *
+	 * Traverse the console_cmdline array in reverse order to be
+	 * sure that if this console is preferred then it will be the first
+	 * matching entry.  We use the invariant that is maintained in
+	 * __add_preferred_console().
 	 */
-	for (i = 0, c = console_cmdline;
-	     i < MAX_CMDLINECONSOLES && c->name[0];
-	     i++, c++) {
+	for (i = console_cmdline_cnt - 1; i >= 0; i--) {
+		c = console_cmdline + i;
+
 		if (!newcon->match ||
 		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
 			/* default matching */
@@ -2484,9 +2515,9 @@ void register_console(struct console *newcon)
 		}
 
 		newcon->flags |= CON_ENABLED;
-		if (i == selected_console) {
+		if (i == preferred_console) {
 			newcon->flags |= CON_CONSDEV;
-			preferred_console = selected_console;
+			has_preferred = true;
 		}
 		break;
 	}