From: Lorenzo Stoakes
> Sent: 09 June 2023 09:49
> On Fri, Jun 09, 2023 at 08:09:45AM +0100, Lorenzo Stoakes wrote:
> > On Fri, Jun 09, 2023 at 02:13:09PM +0800, Lu Hongfei wrote:
> > > It would be better to replace the traditional ternary conditional
> > > operator with min() in zero_iter
> > >
> > > Signed-off-by: Lu Hongfei <luhongfei@xxxxxxxx>
> > > ---
> > > mm/vmalloc.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index 29077d61ff81..42df032e6c27
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -3571,7 +3571,7 @@ static size_t zero_iter(struct iov_iter *iter, size_t count)
> > > while (remains > 0) {
> > > size_t num, copied;
> > >
> > > - num = remains < PAGE_SIZE ? remains : PAGE_SIZE;
> > > + num = min(remains, PAGE_SIZE);
>
> OK, as per the pedantic test bot, you'll need to change this to:-
>
> num = min_t(size_t, remains, PAGE_SIZE);
There has to be a valid reason why min/max have strong type checks.
Using min_t() all the time is just subverting them and means that
bugs are more likely than if the extra tests in min() were absent.
The problem here is that size_t is 'unsigned int' but PAGE_SIZE
'unsigned long'.
A 'safe' change is min(remains + 0ULL, PAGE_SIZE).
But, in reality, min/max should always be valid when one
value is a constant between 0 and MAX_INT.
The constant just needs forcing to 'signed int' (eg assigning
to a temporary on that type) before the comparison (etc).
David
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