linux-kernel - [PATCH 3.19 048/101] writeback: add missing INITIAL_JIFFIES init in global_update

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Message-Id: <20150417132516.481981971@linuxfoundation.org>
Date:	Fri, 17 Apr 2015 15:28:36 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	Jan Kara <jack@...e.cz>, Wu Fengguang <fengguang.wu@...el.com>,
	Jens Axboe <axboe@...nel.dk>, Jens Axboe <axboe@...com>
Subject: [PATCH 3.19 048/101] writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()

3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tejun Heo <tj@...nel.org>

commit 7d70e15480c0450d2bfafaad338a32e884fc215e upstream.

global_update_bandwidth() uses static variable update_time as the
timestamp for the last update but forgets to initialize it to
INITIALIZE_JIFFIES.

This means that global_dirty_limit will be 5 mins into the future on
32bit and some large amount jiffies into the past on 64bit.  This
isn't critical as the only effect is that global_dirty_limit won't be
updated for the first 5 mins after booting on 32bit machines,
especially given the auxiliary nature of global_dirty_limit's role -
protecting against global dirty threshold's sudden dips; however, it
does lead to unintended suboptimal behavior.  Fix it.

Fixes: c42843f2f0bb ("writeback: introduce smoothed global dirty limit")
Signed-off-by: Tejun Heo <tj@...nel.org>
Acked-by: Jan Kara <jack@...e.cz>
Cc: Wu Fengguang <fengguang.wu@...el.com>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Jens Axboe <axboe@...com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/page-writeback.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -922,7 +922,7 @@ static void global_update_bandwidth(unsi
 				    unsigned long now)
 {
 	static DEFINE_SPINLOCK(dirty_lock);
-	static unsigned long update_time;
+	static unsigned long update_time = INITIAL_JIFFIES;
 
 	/*
 	 * check locklessly first to optimize away locking for the most time


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