Merge branch 'for-5.18-panic-deadlocks' into for-linus (1ccd85f5) · Commits · EulixOS / Software / Kernel

kernel/printk/printk.c

+54 −1

Original line number	Diff line number	Diff line
		@@ -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"
		@@ -258,6 +264,11 @@ 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
		@@ -1844,6 +1855,16 @@ 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);
		@@ -2219,6 +2240,10 @@ 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;
		@@ -2586,6 +2611,25 @@ static int have_callable_console(void)
		return 0;
		}

		/*
		* 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?
		*
		@@ -2616,6 +2660,7 @@ 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;
		@@ -2670,6 +2715,10 @@ void console_unlock(void)
		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)) {
		@@ -2729,6 +2778,10 @@ void console_unlock(void)
		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();
		}
		@@ -2746,7 +2799,7 @@ void console_unlock(void)
		* 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);