diff options
| author | Rik van Riel <riel@redhat.com> | 2014-05-06 12:50:01 -0700 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2014-06-09 13:29:09 +0100 |
| commit | a46ea9a3af2d816884b3a04f1f570f45f4455a0f (patch) | |
| tree | 6732c361764b473db8c96e382a5d80bcde952b84 | |
| parent | 2f181f630872a363d0eae4624eca93e1c56aa4d1 (diff) | |
mm/page-writeback.c: fix divide by zero in pos_ratio_polynom
commit d5c9fde3dae750889168807038243ff36431d276 upstream.
It is possible for "limit - setpoint + 1" to equal zero, after getting
truncated to a 32 bit variable, and resulting in a divide by zero error.
Using the fully 64 bit divide functions avoids this problem. It also
will cause pos_ratio_polynom() to return the correct value when
(setpoint - limit) exceeds 2^32.
Also uninline pos_ratio_polynom, at Andrew's request.
Signed-off-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2:
Adjust context - pos_ratio_polynom() is not a separate function]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | mm/page-writeback.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 022622dbf42..d2ac057008f 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -559,7 +559,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, * => fast response on large errors; small oscillation near setpoint */ setpoint = (freerun + limit) / 2; - x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, + x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, limit - setpoint + 1); pos_ratio = x; pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; @@ -625,7 +625,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, x_intercept = bdi_setpoint + span; if (bdi_dirty < x_intercept - span / 4) { - pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), + pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty), x_intercept - bdi_setpoint + 1); } else pos_ratio /= 4; |