printk: Keep non-panic-CPUs out of console lock

When in a panic situation, non-panic CPUs should avoid holding the
console lock so as not to contend with the panic CPU. This is already
implemented with abandon_console_lock_in_panic(), which is checked
after each printed line. However, non-panic CPUs should also avoid
trying to acquire the console lock during a panic.

Modify console_trylock() to fail and console_lock() to block() when
called from a non-panic CPU during a panic.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230717194607.145135-4-john.ogness@linutronix.de

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7aa9dbee12e87b6fb4efa194faa58118911e9b16..7219991885e6f9af945e76d33b06533fc4d8c87d 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2583,6 +2583,25 @@ static int console_cpu_notify(unsigned int cpu)
        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();
+}
+
 /**
  * console_lock - block the console subsystem from printing
  *
@@ -2595,6 +2614,10 @@ void console_lock(void)
 {
        might_sleep();
 
+       /* On panic, the console_lock must be left to the panic cpu. */
+       while (abandon_console_lock_in_panic())
+               msleep(1000);
+
        down_console_sem();
        if (console_suspended)
                return;
@@ -2613,6 +2636,9 @@ EXPORT_SYMBOL(console_lock);
  */
 int console_trylock(void)
 {
+       /* On panic, the console_lock must be left to the panic cpu. */
+       if (abandon_console_lock_in_panic())
+               return 0;
        if (down_trylock_console_sem())
                return 0;
        if (console_suspended) {
@@ -2631,25 +2657,6 @@ int is_console_locked(void)
 }
 EXPORT_SYMBOL(is_console_locked);
 
-/*
- * 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();
-}
-
 /*
  * Check if the given console is currently capable and allowed to print
  * records.