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SubjectRe: [PATCH -next 2/2] bcache: Use max_t() when comparing different types
On Thu, 6 Feb 2014 21:45:36 +0100 Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> > --- a/drivers/md/bcache/btree.c~bcache-drop-l-suffix-when-comparing-ssize_t-with-0-fix
> > +++ a/drivers/md/bcache/btree.c
> > @@ -1805,7 +1805,7 @@ static bool btree_insert_key(struct btre
> >
> > static size_t insert_u64s_remaining(struct btree *b)
> > {
> > - ssize_t ret = bch_btree_keys_u64s_remaining(&b->keys);
> > + size_t ret = bch_btree_keys_u64s_remaining(&b->keys);
> >
> > /*
> > * Might land in the middle of an existing extent and have to split it
> > @@ -1813,7 +1813,7 @@ static size_t insert_u64s_remaining(stru
> > if (b->keys.ops->is_extents)
> > ret -= KEY_MAX_U64S;
>
> I think the reason is the line above: with size_t, ret may become a big
> positive number when the subtraction wraps below zero.

Well, I assumed that case would be a bug - otherwise the programmer
would have commented such a subtlety. Wouldn't he?

> >
> > - return max(ret, 0);
> > + return max_t(size_t, ret, 0);
>
> That part is OK, cfr. my v1 (which I had planned to send out as v3 again).

It needs to be ssize_t.


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