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lib: percpu_counter_sub

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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>
This commit is contained in:
Peter Zijlstra
2007-10-16 23:25:42 -07:00
committed by Linus Torvalds
parent aa0dff2d09
commit 3cb4f9fa0c
4 changed files with 8 additions and 3 deletions
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2
fs/ext2/balloc.c
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@@ -124,7 +124,7 @@ static int reserve_blocks(struct super_block *sb, int count)
return 0;
}
percpu_counter_add(&sbi->s_freeblocks_counter, -count);
percpu_counter_sub(&sbi->s_freeblocks_counter, count);
sb->s_dirt = 1;
return count;
}