tree c0d59e0a254d7c4b9f31ee3a4873423cc200ee35
parent b72d0ffb5dbc4070089b36230b98687ca4577cbc
author Andrey Ryabinin <aryabinin@virtuozzo.com> 1458078927 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1458086116 -0700

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>