diff options
| -rw-r--r-- | kernel/printk/printk.c | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 9644f6e5bf15..7aa9dbee12e8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3043,10 +3043,28 @@ EXPORT_SYMBOL(console_conditional_schedule); void console_unblank(void) { + bool found_unblank = false; struct console *c; int cookie; /* + * First check if there are any consoles implementing the unblank() + * callback. If not, there is no reason to continue and take the + * console lock, which in particular can be dangerous if + * @oops_in_progress is set. + */ + cookie = console_srcu_read_lock(); + for_each_console_srcu(c) { + if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) { + found_unblank = true; + break; + } + } + console_srcu_read_unlock(cookie); + if (!found_unblank) + return; + + /* * Stop console printing because the unblank() callback may * assume the console is not within its write() callback. * @@ -3054,6 +3072,16 @@ void console_unblank(void) * In that case, attempt a trylock as best-effort. */ if (oops_in_progress) { + /* Semaphores are not NMI-safe. */ + if (in_nmi()) + return; + + /* + * Attempting to trylock the console lock can deadlock + * if another CPU was stopped while modifying the + * semaphore. "Hope and pray" that this is not the + * current situation. + */ if (down_trylock_console_sem() != 0) return; } else |