linux-kernel - Re: [uml-devel] BUG: soft lockup for a user mode linux image

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Date:	Fri, 11 Oct 2013 16:57:01 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	Richard Weinberger <richard@....at>, Jan Kara <jack@...e.cz>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	UML devel <user-mode-linux-devel@...ts.sourceforge.net>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	hannes@...xchg.org, darrick.wong@...cle.com,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [uml-devel] BUG: soft lockup for a user mode linux image

On Fri, Oct 11, 2013 at 10:42:19AM +0200, Toralf Förster wrote:
> yeah, now the picture becomes more clear
> ...
> net.core.warnings = 0                                                                         [ ok ]
> ick: pause : -717
>                  ick : min_pause : -177
>                                    ick : max_pause : -717
>                                                      ick: pages_dirtied : 14
>                                                                             ick: task_ratelimit: 0

Great and thanks! So it's the max pause calculation went wrong.
Would help you try the below patch?

>From 5420b9bbe42dd0a366d7615e9f3d3724cee725c4 Mon Sep 17 00:00:00 2001
From: Fengguang Wu <fengguang.wu@...el.com>
Date: Fri, 11 Oct 2013 16:53:26 +0800
Subject: [PATCH] fix bdi max pause calculation

Signed-off-by: Fengguang Wu <fengguang.wu@...el.com>
---
 mm/page-writeback.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 3f0c895..241a746 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1104,11 +1104,11 @@ static unsigned long dirty_poll_interval(unsigned long dirty,
 	return 1;
 }
 
-static long bdi_max_pause(struct backing_dev_info *bdi,
-			  unsigned long bdi_dirty)
+static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
+				   unsigned long bdi_dirty)
 {
-	long bw = bdi->avg_write_bandwidth;
-	long t;
+	unsigned long bw = bdi->avg_write_bandwidth;
+	unsigned long t;
 
 	/*
 	 * Limit pause time for small memory systems. If sleeping for too long
@@ -1120,7 +1120,7 @@ static long bdi_max_pause(struct backing_dev_info *bdi,
 	t = bdi_dirty / (1 + bw / roundup_pow_of_two(1 + HZ / 8));
 	t++;
 
-	return min_t(long, t, MAX_PAUSE);
+	return min_t(unsigned long, t, MAX_PAUSE);
 }
 
 static long bdi_min_pause(struct backing_dev_info *bdi,
-- 
1.7.10.4

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