From: paul.szabo@sydney.edu.au Date: Sun, 20 Jan 2013 00:02:10 +0000 (+1100) Subject: Negative (setpoint-dirty) in bdi_position_ratio() X-Git-Tag: v3.2.60~34 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2f181f630872a363d0eae4624eca93e1c56aa4d1;p=pandora-kernel.git Negative (setpoint-dirty) in bdi_position_ratio() commit ed84825b785ceb932af7dd5aa08614801721320b upstream. In bdi_position_ratio(), get difference (setpoint-dirty) right even when negative. Both setpoint and dirty are unsigned long, the difference was zero-padded thus wrongly sign-extended to s64. This issue affects all 32-bit architectures, does not affect 64-bit architectures where long and s64 are equivalent. In this function, dirty is between freerun and limit, the pseudo-float x is between [-1,1], expected to be negative about half the time. With zero-padding, instead of a small negative x we obtained a large positive one so bdi_position_ratio() returned garbage. Casting the difference to s64 also prevents overflow with left-shift; though normally these numbers are small and I never observed a 32-bit overflow there. (This patch does not solve the PAE OOM issue.) Paul Szabo psz@maths.usyd.edu.au http://www.maths.usyd.edu.au/u/psz/ School of Mathematics and Statistics University of Sydney Australia Reviewed-by: Jan Kara Reported-by: Paul Szabo Reference: http://bugs.debian.org/695182 Signed-off-by: Paul Szabo Signed-off-by: Fengguang Wu Signed-off-by: Ben Hutchings --- Reading git-diff-tree failed