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authorAndrey Ryabinin <aryabinin@virtuozzo.com>2016-03-15 14:55:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-15 16:55:16 -0700
commitd59b1087a98e402ed9a7cc577f4da435f9a555f5 (patch)
treec0d59e0a254d7c4b9f31ee3a4873423cc200ee35
parentb72d0ffb5dbc4070089b36230b98687ca4577cbc (diff)
mm/page-writeback: fix dirty_ratelimit calculation
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>
-rw-r--r--mm/page-writeback.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 6fe7d15bd1f7..d782cbab735a 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1169,6 +1169,7 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
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
@@ -1293,11 +1294,11 @@ static void wb_update_dirty_ratelimit(struct dirty_throttle_control *dtc,
* 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;