relay-fix-timer-madness.patch

From 5700b1ae8c1b1969cc3739e4621699e45e94a4ab Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:44:07 -0500
Subject: [PATCH] relay: fix timer madness

commit f6a6d1e5259459b6791250d773c5a0ad9a8de45a in tip.

remove timer calls (!!!) from deep within the tracing infrastructure.
This was totally bogus code that can cause lockups and worse.  Poll
the buffer every 2 jiffies for now.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/relay.c b/kernel/relay.c
index c705a41..4da323b 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -343,6 +343,10 @@ static void wakeup_readers(unsigned long data)
 {
 	struct rchan_buf *buf = (struct rchan_buf *)data;
 	wake_up_interruptible(&buf->read_wait);
+	/*
+	 * Stupid polling for now:
+	 */
+	mod_timer(&buf->timer, jiffies + 1);
 }
 
 /**
@@ -360,6 +364,7 @@ static void __relay_reset(struct rchan_buf *buf, unsigned int init)
 		init_waitqueue_head(&buf->read_wait);
 		kref_init(&buf->kref);
 		setup_timer(&buf->timer, wakeup_readers, (unsigned long)buf);
+		mod_timer(&buf->timer, jiffies + 1);
 	} else
 		del_timer_sync(&buf->timer);
 
@@ -740,15 +745,6 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
 		else
 			buf->early_bytes += buf->chan->subbuf_size -
 					    buf->padding[old_subbuf];
-		smp_mb();
-		if (waitqueue_active(&buf->read_wait))
-			/*
-			 * Calling wake_up_interruptible() from here
-			 * will deadlock if we happen to be logging
-			 * from the scheduler (trying to re-grab
-			 * rq->lock), so defer it.
-			 */
-			mod_timer(&buf->timer, jiffies + 1);
 	}
 
 	old = buf->data;
-- 
1.7.1.1