3.10.102-> 3.10.103

1 files changed, 34 insertions, 1 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index b30c61814..95cfcfd30 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -2161,7 +2161,7 @@ void console_unlock(void)
 	static u64 seen_seq;
 	unsigned long flags;
 	bool wake_klogd = false;
-	bool retry;
+	bool do_cond_resched, retry;
 #ifdef LOG_TOO_MUCH_WARNING
     unsigned long total_log_size = 0;
     unsigned long long t1 = 0, t2 = 0;
@@ -2174,6 +2174,18 @@ void console_unlock(void)
 		return;
 	}
 
+	/*
+	 * Console drivers are called under logbuf_lock, so
+	 * @console_may_schedule should be cleared before; however, we may
+	 * end up dumping a lot of lines, for example, if called from
+	 * console registration path, and should invoke cond_resched()
+	 * between lines if allowable.  Not doing so can cause a very long
+	 * scheduling stall on a slow console leading to RCU stall and
+	 * softlockup warnings which exacerbate the issue with more
+	 * messages practically incapacitating the system.
+	 */
+	do_cond_resched = console_may_schedule;
+
 	console_may_schedule = 0;
 
 	/* flush buffered message fragment immediately to console */
@@ -2269,6 +2281,8 @@ skip:
         call_console_drivers(level, text, len);
 #endif
 		local_irq_restore(flags);
+		if (do_cond_resched)
+			cond_resched();
 	}
 	console_locked = 0;
 	mutex_release(&console_lock_dep_map, 1, _RET_IP_);
@@ -2337,6 +2351,25 @@ void console_unblank(void)
 	console_unlock();
 }
 
+/**
+ * console_flush_on_panic - flush console content on panic
+ *
+ * Immediately output all pending messages no matter what.
+ */
+void console_flush_on_panic(void)
+{
+	/*
+	 * If someone else is holding the console lock, trylock will fail
+	 * and may_schedule may be set.  Ignore and proceed to unlock so
+	 * that messages are flushed out.  As this can be called from any
+	 * context and we don't want to get preempted while flushing,
+	 * ensure may_schedule is cleared.
+	 */
+	console_trylock();
+	console_may_schedule = 0;
+	console_unlock();
+}
+
 /*
  * Return the console tty driver structure and its associated index
  */