1 files changed, 21 insertions, 3 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 35185392173f..37dff3429adb 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -782,7 +782,7 @@ static inline int can_use_console(unsigned int cpu)
 static int console_trylock_for_printk(unsigned int cpu)
         __releases(&logbuf_lock)
 {
-        int retval = 0;
+        int retval = 0, wake = 0;
 
         if (console_trylock()) {
                 retval = 1;
@@ -795,12 +795,14 @@ static int console_trylock_for_printk(unsigned int cpu)
                  */
                 if (!can_use_console(cpu)) {
                         console_locked = 0;
-                        up(&console_sem);
+                        wake = 1;
                         retval = 0;
                 }
         }
         printk_cpu = UINT_MAX;
         spin_unlock(&logbuf_lock);
+        if (wake)
+                up(&console_sem);
         return retval;
 }
 static const char recursion_bug_msg [] =
@@ -1242,7 +1244,7 @@ void console_unlock(void)
 {
         unsigned long flags;
         unsigned _con_start, _log_end;
-        unsigned wake_klogd = 0;
+        unsigned wake_klogd = 0, retry = 0;
 
         if (console_suspended) {
                 up(&console_sem);
@@ -1251,6 +1253,7 @@ void console_unlock(void)
 
         console_may_schedule = 0;
 
+again:
         for ( ; ; ) {
                 spin_lock_irqsave(&logbuf_lock, flags);
                 wake_klogd |= log_start - log_end;
@@ -1271,8 +1274,23 @@ void console_unlock(void)
         if (unlikely(exclusive_console))
                 exclusive_console = NULL;
 
+        spin_unlock(&logbuf_lock);
+
         up(&console_sem);
+
+        /*
+         * Someone could have filled up the buffer again, so re-check if there's
+         * something to flush. In case we cannot trylock the console_sem again,
+         * there's a new owner and the console_unlock() from them will do the
+         * flush, no worries.
+         */
+        spin_lock(&logbuf_lock);
+        if (con_start != log_end)
+                retry = 1;
         spin_unlock_irqrestore(&logbuf_lock, flags);
+        if (retry && console_trylock())
+                goto again;
+
         if (wake_klogd)
                 wake_up_klogd();
 }