tree d1f45445fa98bd41a2f8986781f7c62b470a6b8d
parent aa0dff2d09bfa50b7d02714a45920c64568e699d
author Peter Zijlstra <a.p.zijlstra@chello.nl> 1192602342 -0700
committer Linus Torvalds <torvalds@woody.linux-foundation.org> 1192635764 -0700

lib: percpu_counter_sub

Hugh spotted that some code does:
  percpu_counter_add(&counter, -unsignedlong)

which, when the amount argument is of type s32, sort-of works thanks to
two's-complement. However when we'd change the type to s64 this breaks on 32bit
machines, because the promotion rules zero extend the unsigned number.

Provide percpu_counter_sub() to hide the s64 cast. That is:
  percpu_counter_sub(&counter, foo)
is equal to:
  percpu_counter_add(&counter, -(s64)foo);

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>