This is a note to let you know that I've just added the patch titled
mm/page-writeback: fix dirty_ratelimit calculation
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-page-writeback-fix-dirty_ratelimit-calculation.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From d59b1087a98e402ed9a7cc577f4da435f9a555f5 Mon Sep 17 00:00:00 2001
From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Date: Tue, 15 Mar 2016 14:55:27 -0700
Subject: mm/page-writeback: fix dirty_ratelimit calculation
From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
commit d59b1087a98e402ed9a7cc577f4da435f9a555f5 upstream.
Calculation of dirty_ratelimit sometimes is not correct. E.g. initial
values of dirty_ratelimit == INIT_BW and step == 0, lead to the
following result:
UBSAN: Undefined behaviour in ../mm/page-writeback.c:1286:7
shift exponent 25600 is too large for 64-bit type 'long unsigned int'
The fix is straightforward - make step 0 if the shift exponent is too
big.
Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1162,6 +1162,7 @@ static void wb_update_dirty_ratelimit(st
unsigned long balanced_dirty_ratelimit;
unsigned long step;
unsigned long x;
+ unsigned long shift;
/*
* The dirty rate will match the writeout rate in long term, except
@@ -1286,11 +1287,11 @@ static void wb_update_dirty_ratelimit(st
* rate itself is constantly fluctuating. So decrease the track speed
* when it gets close to the target. Helps eliminate pointless tremors.
*/
- step >>= dirty_ratelimit / (2 * step + 1);
- /*
- * Limit the tracking speed to avoid overshooting.
- */
- step = (step + 7) / 8;
+ shift = dirty_ratelimit / (2 * step + 1);
+ if (shift < BITS_PER_LONG)
+ step = DIV_ROUND_UP(step >> shift, 8);
+ else
+ step = 0;
if (dirty_ratelimit < balanced_dirty_ratelimit)
dirty_ratelimit += step;
Patches currently in stable-queue which might be from aryabinin@xxxxxxxxxxxxx are
queue-4.4/net-mac80211-debugfs.c-prevent-build-failure-with-config_ubsan-y.patch
queue-4.4/mm-page-writeback-fix-dirty_ratelimit-calculation.patch