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%3Ba=su...
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@vger.kernel.org know about it.
From d59b1087a98e402ed9a7cc577f4da435f9a555f5 Mon Sep 17 00:00:00 2001
From: Andrey Ryabinin aryabinin@virtuozzo.com Date: Tue, 15 Mar 2016 14:55:27 -0700 Subject: mm/page-writeback: fix dirty_ratelimit calculation
From: Andrey Ryabinin aryabinin@virtuozzo.com
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@virtuozzo.com Cc: Wu Fengguang fengguang.wu@intel.com Cc: Tejun Heo tj@kernel.org Cc: Andy Shevchenko andy.shevchenko@gmail.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Mel Gorman mgorman@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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@virtuozzo.com 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