lib: proportion: fix underflow in prop_norm_percpu()
authorPeter Zijlstra <a.p.zijlstra@chello.nl>
Sat, 22 Dec 2007 22:03:29 +0000 (14:03 -0800)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Sun, 23 Dec 2007 20:54:37 +0000 (12:54 -0800)
commitf16b34aa13e8c55085f346bcf07afb2312c56c0a
tree4fba40d99a5907694a1a1de8023f1431204f4f98
parentcc295d0e95063809af31971e4aec1d809247f13b
lib: proportion: fix underflow in prop_norm_percpu()

Zhe Jiang noticed that its possible to underflow pl->events in
prop_norm_percpu() when the value returned by percpu_counter_read() is less
than the error on that read and the period delay > 1.  In that case half might
not trigger the batch increment and the value will be identical on the next
iteration, causing the same half to be subtracted again and again.

Fix this by rewriting the division as a single subtraction instead of a
subtraction loop and using percpu_counter_sum() when the value returned by
percpu_counter_read() is smaller than the error.

The latter is still needed if we want pl->events to shrink properly in the
error region.

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Jiang Zhe <zhe.jiang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
lib/proportions.c