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| author | Andrey Ryabinin <aryabinin@virtuozzo.com> | 2016-03-16 00:55:27 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-03-16 02:55:16 +0300 |
| commit | d59b1087a98e402ed9a7cc577f4da435f9a555f5 (patch) | |
| tree | c0d59e0a254d7c4b9f31ee3a4873423cc200ee35 | |
| parent | b72d0ffb5dbc4070089b36230b98687ca4577cbc (diff) | |
| download | linux-d59b1087a98e402ed9a7cc577f4da435f9a555f5.tar.xz | |
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.c | 11 |
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; |