Commit d5c9fde3 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds

mm/page-writeback.c: fix divide by zero in pos_ratio_polynom

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: default avatarRik van Riel <riel@redhat.com>
Reviewed-by: default avatarMichal 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>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 457c1b27
...@@ -593,14 +593,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) ...@@ -593,14 +593,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
* (5) the closer to setpoint, the smaller |df/dx| (and the reverse) * (5) the closer to setpoint, the smaller |df/dx| (and the reverse)
* => fast response on large errors; small oscillation near setpoint * => fast response on large errors; small oscillation near setpoint
*/ */
static inline long long pos_ratio_polynom(unsigned long setpoint, static long long pos_ratio_polynom(unsigned long setpoint,
unsigned long dirty, unsigned long dirty,
unsigned long limit) unsigned long limit)
{ {
long long pos_ratio; long long pos_ratio;
long x; long x;
x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT,
limit - setpoint + 1); limit - setpoint + 1);
pos_ratio = x; pos_ratio = x;
pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT;
...@@ -842,7 +842,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, ...@@ -842,7 +842,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
x_intercept = bdi_setpoint + span; x_intercept = bdi_setpoint + span;
if (bdi_dirty < x_intercept - span / 4) { 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); x_intercept - bdi_setpoint + 1);
} else } else
pos_ratio /= 4; pos_ratio /= 4;
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment