Merge tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Make %pK behave the same as %p for kptr_restrict == 0 also with
   no_hash_pointers parameter

 - Ignore the default console in the device tree also when console=null
   or console="" is used on the command line

 - Document console=null and console="" behavior

 - Prevent a deadlock and a livelock caused by console_lock in panic()

 - Make console_lock available for panicking CPU

 - Fast query for the next to-be-used sequence number

 - Use the expected return values in printk.devkmsg __setup handler

 - Use the correct atomic operations in wake_up_klogd() irq_work handler

 - Avoid possible unaligned access when handling %4cc printing format

* tag 'printk-for-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  printk: fix return value of printk.devkmsg __setup handler
  vsprintf: Fix %pK with kptr_restrict == 0
  printk: make suppress_panic_printk static
  printk: Set console_set_on_cmdline=1 when __add_preferred_console() is called with user_specified == true
  Docs: printk: add 'console=null|""' to admin/kernel-parameters
  printk: use atomic updates for klogd work
  printk: Drop console_sem during panic
  printk: Avoid livelock with heavy printk during panic
  printk: disable optimistic spin during panic
  printk: Add panic_in_progress helper
  vsprintf: Move space out of string literals in fourcc_string()
  vsprintf: Fix potential unaligned access
  printk: ringbuffer: Improve prb_next_seq() performance

1 files changed, 76 insertions, 9 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82abfaf3c2aa..da03c15ecc89 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -93,6 +93,12 @@ EXPORT_SYMBOL_GPL(console_drivers);
  */
 int __read_mostly suppress_printk;
 
+/*
+ * During panic, heavy printk by other CPUs can delay the
+ * panic and risk deadlock on console resources.
+ */
+static int __read_mostly suppress_panic_printk;
+
 #ifdef CONFIG_LOCKDEP
 static struct lockdep_map console_lock_dep_map = {
 	.name = "console_lock"
@@ -146,8 +152,10 @@ static int __control_devkmsg(char *str)
 
 static int __init control_devkmsg(char *str)
 {
-	if (__control_devkmsg(str) < 0)
+	if (__control_devkmsg(str) < 0) {
+		pr_warn("printk.devkmsg: bad option string '%s'\n", str);
 		return 1;
+	}
 
 	/*
 	 * Set sysctl string accordingly:
@@ -166,7 +174,7 @@ static int __init control_devkmsg(char *str)
 	 */
 	devkmsg_log |= DEVKMSG_LOG_MASK_LOCK;
 
-	return 0;
+	return 1;
 }
 __setup("printk.devkmsg=", control_devkmsg);
 
@@ -257,6 +265,11 @@ static void __up_console_sem(unsigned long ip)
 }
 #define up_console_sem() __up_console_sem(_RET_IP_)
 
+static bool panic_in_progress(void)
+{
+	return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID);
+}
+
 /*
  * This is used for debugging the mess that is the VT code by
  * keeping track if we have the console semaphore held. It's
@@ -1843,6 +1856,16 @@ static int console_trylock_spinning(void)
 	if (console_trylock())
 		return 1;
 
+	/*
+	 * It's unsafe to spin once a panic has begun. If we are the
+	 * panic CPU, we may have already halted the owner of the
+	 * console_sem. If we are not the panic CPU, then we should
+	 * avoid taking console_sem, so the panic CPU has a better
+	 * chance of cleanly acquiring it later.
+	 */
+	if (panic_in_progress())
+		return 0;
+
 	printk_safe_enter_irqsave(flags);
 
 	raw_spin_lock(&console_owner_lock);
@@ -2218,6 +2241,10 @@ asmlinkage int vprintk_emit(int facility, int level,
 	if (unlikely(suppress_printk))
 		return 0;
 
+	if (unlikely(suppress_panic_printk) &&
+	    atomic_read(&panic_cpu) != raw_smp_processor_id())
+		return 0;
+
 	if (level == LOGLEVEL_SCHED) {
 		level = LOGLEVEL_DEFAULT;
 		in_sched = true;
@@ -2324,6 +2351,20 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
 }
 #endif
 
+static void set_user_specified(struct console_cmdline *c, bool user_specified)
+{
+	if (!user_specified)
+		return;
+
+	/*
+	 * @c console was defined by the user on the command line.
+	 * Do not clear when added twice also by SPCR or the device tree.
+	 */
+	c->user_specified = true;
+	/* At least one console defined by the user on the command line. */
+	console_set_on_cmdline = 1;
+}
+
 static int __add_preferred_console(char *name, int idx, char *options,
 				   char *brl_options, bool user_specified)
 {
@@ -2340,8 +2381,7 @@ static int __add_preferred_console(char *name, int idx, char *options,
 		if (strcmp(c->name, name) == 0 && c->index == idx) {
 			if (!brl_options)
 				preferred_console = i;
-			if (user_specified)
-				c->user_specified = true;
+			set_user_specified(c, user_specified);
 			return 0;
 		}
 	}
@@ -2351,7 +2391,7 @@ static int __add_preferred_console(char *name, int idx, char *options,
 		preferred_console = i;
 	strlcpy(c->name, name, sizeof(c->name));
 	c->options = options;
-	c->user_specified = user_specified;
+	set_user_specified(c, user_specified);
 	braille_set_options(c, brl_options);
 
 	c->index = idx;
@@ -2417,7 +2457,6 @@ static int __init console_setup(char *str)
 	*s = 0;
 
 	__add_preferred_console(buf, idx, options, brl_options, true);
-	console_set_on_cmdline = 1;
 	return 1;
 }
 __setup("console=", console_setup);
@@ -2574,6 +2613,25 @@ static int have_callable_console(void)
 }
 
 /*
+ * Return true when this CPU should unlock console_sem without pushing all
+ * messages to the console. This reduces the chance that the console is
+ * locked when the panic CPU tries to use it.
+ */
+static bool abandon_console_lock_in_panic(void)
+{
+	if (!panic_in_progress())
+		return false;
+
+	/*
+	 * We can use raw_smp_processor_id() here because it is impossible for
+	 * the task to be migrated to the panic_cpu, or away from it. If
+	 * panic_cpu has already been set, and we're not currently executing on
+	 * that CPU, then we never will be.
+	 */
+	return atomic_read(&panic_cpu) != raw_smp_processor_id();
+}
+
+/*
  * Can we actually use the console at this time on this cpu?
  *
  * Console drivers may assume that per-cpu resources have been allocated. So
@@ -2603,6 +2661,7 @@ void console_unlock(void)
 {
 	static char ext_text[CONSOLE_EXT_LOG_MAX];
 	static char text[CONSOLE_LOG_MAX];
+	static int panic_console_dropped;
 	unsigned long flags;
 	bool do_cond_resched, retry;
 	struct printk_info info;
@@ -2657,6 +2716,10 @@ skip:
 		if (console_seq != r.info->seq) {
 			console_dropped += r.info->seq - console_seq;
 			console_seq = r.info->seq;
+			if (panic_in_progress() && panic_console_dropped++ > 10) {
+				suppress_panic_printk = 1;
+				pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n");
+			}
 		}
 
 		if (suppress_message_printing(r.info->level)) {
@@ -2716,6 +2779,10 @@ skip:
 		if (handover)
 			return;
 
+		/* Allow panic_cpu to take over the consoles safely */
+		if (abandon_console_lock_in_panic())
+			break;
+
 		if (do_cond_resched)
 			cond_resched();
 	}
@@ -2733,7 +2800,7 @@ skip:
 	 * flush, no worries.
 	 */
 	retry = prb_read_valid(prb, next_seq, NULL);
-	if (retry && console_trylock())
+	if (retry && !abandon_console_lock_in_panic() && console_trylock())
 		goto again;
 }
 EXPORT_SYMBOL(console_unlock);
@@ -3228,7 +3295,7 @@ static DEFINE_PER_CPU(int, printk_pending);
 
 static void wake_up_klogd_work_func(struct irq_work *irq_work)
 {
-	int pending = __this_cpu_xchg(printk_pending, 0);
+	int pending = this_cpu_xchg(printk_pending, 0);
 
 	if (pending & PRINTK_PENDING_OUTPUT) {
 		/* If trylock fails, someone else is doing the printing */
@@ -3262,7 +3329,7 @@ void defer_console_output(void)
 		return;
 
 	preempt_disable();
-	__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+	this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
 	irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
 	preempt_enable();
 }