2 files changed, 34 insertions, 17 deletions

diff --git a/include/linux/console.h b/include/linux/console.h
index 08734e660d41..d0f8a8009490 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -87,6 +87,7 @@ void give_up_console(const struct consw *sw);
 #define CON_CONSDEV     (2) /* Last on the command line */
 #define CON_ENABLED     (4)
 #define CON_BOOT        (8)
+#define CON_ANYTIME     (16) /* Safe to call when cpu is offline */
 
 struct console
 {
diff --git a/kernel/printk.c b/kernel/printk.c
index 19a955619294..6b89dd9d11b6 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -327,7 +327,9 @@ static void __call_console_drivers(unsigned long start, unsigned long end)
         struct console *con;
 
         for (con = console_drivers; con; con = con->next) {
-                if ((con->flags & CON_ENABLED) && con->write)
+                if ((con->flags & CON_ENABLED) && con->write &&
+                                (cpu_online(smp_processor_id()) ||
+                                (con->flags & CON_ANYTIME)))
                         con->write(con, &LOG_BUF(start), end - start);
         }
 }
@@ -453,6 +455,18 @@ __attribute__((weak)) unsigned long long printk_clock(void)
         return sched_clock();
 }
 
+/* Check if we have any console registered that can be called early in boot. */
+static int have_callable_console(void)
+{
+        struct console *con;
+
+        for (con = console_drivers; con; con = con->next)
+                if (con->flags & CON_ANYTIME)
+                        return 1;
+
+        return 0;
+}
+
 /**
  * printk - print a kernel message
  * @fmt: format string
@@ -566,27 +580,29 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                         log_level_unknown = 1;
         }
 
-        if (!cpu_online(smp_processor_id())) {
+        if (!down_trylock(&console_sem)) {
                 /*
-                 * Some console drivers may assume that per-cpu resources have
-                 * been allocated.  So don't allow them to be called by this
-                 * CPU until it is officially up.  We shouldn't be calling into
-                 * random console drivers on a CPU which doesn't exist yet..
+                 * We own the drivers.  We can drop the spinlock and
+                 * let release_console_sem() print the text, maybe ...
                  */
+                console_locked = 1;
                 printk_cpu = UINT_MAX;
                 spin_unlock_irqrestore(&logbuf_lock, flags);
-                goto out;
-        }
-        if (!down_trylock(&console_sem)) {
-                console_locked = 1;
+
                 /*
-                 * We own the drivers.  We can drop the spinlock and let
-                 * release_console_sem() print the text
+                 * Console drivers may assume that per-cpu resources have
+                 * been allocated. So unless they're explicitly marked as
+                 * being able to cope (CON_ANYTIME) don't call them until
+                 * this CPU is officially up.
                  */
-                printk_cpu = UINT_MAX;
-                spin_unlock_irqrestore(&logbuf_lock, flags);
-                console_may_schedule = 0;
-                release_console_sem();
+                if (cpu_online(smp_processor_id()) || have_callable_console()) {
+                        console_may_schedule = 0;
+                        release_console_sem();
+                } else {
+                        /* Release by hand to avoid flushing the buffer. */
+                        console_locked = 0;
+                        up(&console_sem);
+                }
         } else {
                 /*
                  * Someone else owns the drivers.  We drop the spinlock, which
@@ -596,7 +612,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                 printk_cpu = UINT_MAX;
                 spin_unlock_irqrestore(&logbuf_lock, flags);
         }
-out:
+
         preempt_enable();
         return printed_len;
 }