linux-kernel - [PATCH] async: fix __lowest_in

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Message-ID: <20090112101601.7cec05d5@infradead.org>
Date:	Mon, 12 Jan 2009 10:16:01 +0000
From:	Arjan van de Ven <arjan@...radead.org>
To:	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] async: fix __lowest_in_progress()

>From 24bafdeb8a42e2e43a1928ca72159e6ff90cfe85 Mon Sep 17 00:00:00 2001
From: Arjan van de Ven <arjan@...ux.intel.com>
Date: Sun, 11 Jan 2009 15:35:01 +0000
Subject: [PATCH] async: fix __lowest_in_progress()

At 37000 feet somewhere near Greenland I woke up from a half-sleep with the 
realisation that __lowest_in_progress() is buggy. After landing I checked 
and there were indeed 2 problems with it; this patch fixes both:
* The order of the list checks was wrong
* The locking was not correct.

Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
---
 kernel/async.c |   21 ++++++++++++++++-----
 1 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel/async.c b/kernel/async.c
index f286e9f..608b32b 100644
--- a/kernel/async.c
+++ b/kernel/async.c
@@ -90,12 +90,12 @@ extern int initcall_debug;
 static async_cookie_t  __lowest_in_progress(struct list_head *running)
 {
 	struct async_entry *entry;
-	if (!list_empty(&async_pending)) {
-		entry = list_first_entry(&async_pending,
+	if (!list_empty(running)) {
+		entry = list_first_entry(running,
 			struct async_entry, list);
 		return entry->cookie;
-	} else if (!list_empty(running)) {
-		entry = list_first_entry(running,
+	} else if (!list_empty(&async_pending)) {
+		entry = list_first_entry(&async_pending,
 			struct async_entry, list);
 		return entry->cookie;
 	} else {
@@ -104,6 +104,17 @@ static async_cookie_t  __lowest_in_progress(struct list_head *running)
 	}
 
 }
+
+static async_cookie_t  lowest_in_progress(struct list_head *running)
+{
+	unsigned long flags;
+	async_cookie_t ret;
+
+	spin_lock_irqsave(&async_lock, flags);
+	ret = __lowest_in_progress(running);
+	spin_unlock_irqrestore(&async_lock, flags);
+	return ret;
+}
 /*
  * pick the first pending entry and run it
  */
@@ -229,7 +240,7 @@ void async_synchronize_cookie_special(async_cookie_t cookie, struct list_head *r
 		starttime = ktime_get();
 	}
 
-	wait_event(async_done, __lowest_in_progress(running) >= cookie);
+	wait_event(async_done, lowest_in_progress(running) >= cookie);
 
 	if (initcall_debug && system_state == SYSTEM_BOOTING) {
 		endtime = ktime_get();
-- 
1.6.0.6



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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