relay-fix-timer-madness.patch

From 4037318bf258cd420ed2b0932b4bdefb107aaefd 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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 kernel/relay.c |   14 +++++---------
 1 files changed, 5 insertions(+), 9 deletions(-)

diff --git a/kernel/relay.c b/kernel/relay.c
index 3d97f28..fd0e0e7 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;
-- 
1.7.0.4