Re: [PATCH] mm: util: update the kerneldoc for kstrdup_const()

Joe Perches
2020-06-30T14:19:02Z

On Tue, 2020-06-30 at 10:57 +0200, David Hildenbrand wrote:
> On 29.06.20 21:21, Joe Perches wrote:
> > On Mon, 2020-06-29 at 12:54 +0200, David Hildenbrand wrote:
> > > On 28.06.20 19:37, Joe Perches wrote:
> > > > On Sun, 2020-06-28 at 17:25 +0200, Bartosz Golaszewski wrote:
> > > > > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> > > > >
> > > > > Memory allocated with kstrdup_const() must not be passed to regular
> > > > > krealloc() as it is not aware of the possibility of the chunk residing
> > > > > in .rodata. Since there are no potential users of krealloc_const()
> > > > > at the moment, let's just update the doc to make it explicit.
> > > >
> > > > Another option would be to return NULL if it's
> > > > used from krealloc with a pointer into rodata
> > []
> > > > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > []
> > > > @@ -1683,6 +1683,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
> > > > * @new_size: how many bytes of memory are required.
> > > > * @flags: the type of memory to allocate.
> > > > *
> > > > + * If the object pointed to is in rodata (likely from kstrdup_const)
> > > > + * %NULL is returned.
> > > > + *
> > []
> > > Won't we have similar issues if somebody would do a kfree() instead of a
> > > kfree_const()? So I think the original patch makes sense.
> >
> > Which is why I also suggested making kfree work for
> > more types of memory freeing earlier this month.
> >
> > https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/
[]
> what's the real benefit that is worth spending extra runtime cycles?

I very much doubt there is an actual instance
where the runtime cycles matter. Where could
there be a fast-path instance of free?

ANd kvfree consolidation and coding simplicity
make it somewhat useful.