On Tue, Apr 30, 2024 at 02:09:10PM +0200, Vlastimil Babka wrote:
> On 4/29/24 5:03 AM, Matthew Wilcox wrote:
> > On Sun, Apr 28, 2024 at 05:26:44PM +0300, Dan Carpenter wrote:
> >> Currently, if an automatically freed allocation is an error pointer that
> >> will lead to a crash. An example of this is in wm831x_gpio_dbg_show().
> >>
> >> 171 char *label __free(kfree) = gpiochip_dup_line_label(chip, i);
> >> 172 if (IS_ERR(label)) {
> >> 173 dev_err(wm831x->dev, "Failed to duplicate label\n");
> >> 174 continue;
> >> 175 }
> >>
> >> The auto clean up function should check for error pointers as well,
> >> otherwise we're going to keep hitting issues like this.
> >>
> >> Fixes: 54da6a092431 ("locking: Introduce __cleanup() based infrastructure")
> >> Cc: <stable@xxxxxxxxxxxxxxx>
> >> Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> >> ---
> >> Obviously, the fixes tag isn't very fair but it will tell the -stable
> >> tools how far to backport this.
> >>
> >> include/linux/slab.h | 4 ++--
> >> 1 files changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/include/linux/slab.h b/include/linux/slab.h
> >> index 4cc37ef22aae..5f5766219375 100644
> >> --- a/include/linux/slab.h
> >> +++ b/include/linux/slab.h
> >> @@ -279,7 +279,7 @@ void kfree(const void *objp);
> >> void kfree_sensitive(const void *objp);
> >> size_t __ksize(const void *objp);
> >>
> >> -DEFINE_FREE(kfree, void *, if (_T) kfree(_T))
> >> +DEFINE_FREE(kfree, void *, if (!IS_ERR_OR_NULL(_T)) kfree(_T))
> >
> > Wait, why do we check 'if (_T)' at all? kfree() already handles NULL
> > pointers just fine. I wouldn't be averse to making it handle error
> > pointers either.
>
> Making kfree() handle IS_ERR() is perhaps a discussion for something else
> than a stable fix. But Christoph has a point that kfree() checks
> ZERO_OR_NULL_PTR. Here we check IS_ERR_OR_NULL. How about we checked only
> IS_ERR here so it makes some sense?
>
I wondered why Peter Z wrote it like this as well... I think he did
it so the compiler can figure out which calls to kfree() are unnecessary
and remove them. These functions are inline and kfree() is not. I
haven't measured to see if it actually results in a space savings but
the theory is sound.
regards,
dan carpenter
