path: root/fs
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authorpaul.szabo@sydney.edu.au <paul.szabo@sydney.edu.au>2013-01-20 11:02:10 +1100
committerFengguang Wu <fengguang.wu@intel.com>2013-01-24 22:22:22 +0800
commited84825b785ceb932af7dd5aa08614801721320b (patch)
treeb3f704912b4d1496c8317c04bb86c817c4e1afcd /fs
parent10ee27a06cc8eb57f83342a8eabcb75deb872d52 (diff)
Negative (setpoint-dirty) in bdi_position_ratio()
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 <jack@suse.cz> Reported-by: Paul Szabo <psz@maths.usyd.edu.au> Reference: http://bugs.debian.org/695182 Signed-off-by: Paul Szabo <psz@maths.usyd.edu.au> Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
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