| From | Ben Hutchings <> | Date | Sat, 07 Jun 2014 02:26:29 +0100 | Subject | [PATCH 3.2 60/92] mm/page-writeback.c: fix divide by zero in pos_ratio_polynom |
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3.2.60-rc1 review patch. If anyone has any objections, please let me know.
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From: Rik van Riel <riel@redhat.com>
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> --- mm/page-writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -559,7 +559,7 @@ static unsigned long bdi_position_ratio( * => 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( 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;
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