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SubjectRe: [PATCH 12/39] dm: drop null test before destroy functions
On Mon, Sep 14 2015 at  9:46am -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

>
>
> On Sun, 13 Sep 2015, Julia Lawall wrote:
>
> > Remove unneeded NULL test.
> >
> > The semantic patch that makes this change is as follows:
> > (http://coccinelle.lip6.fr/)
> >
> > // <smpl>
> > @@ expression x; @@
> > -if (x != NULL)
> > \(kmem_cache_destroy\|mempool_destroy\|dma_pool_destroy\)(x);
> > // </smpl>
> >
> > Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
> >
> > ---
> > drivers/md/dm-bufio.c | 3 +--
> > drivers/md/dm-cache-target.c | 3 +--
> > drivers/md/dm-crypt.c | 6 ++----
> > drivers/md/dm-io.c | 3 +--
> > drivers/md/dm-log-userspace-base.c | 3 +--
> > drivers/md/dm-region-hash.c | 4 +---
> > drivers/md/dm.c | 13 ++++---------
> > 7 files changed, 11 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
> > index 83cc52e..8ad39b6 100644
> > --- a/drivers/md/dm-bufio.c
> > +++ b/drivers/md/dm-bufio.c
> > @@ -1864,8 +1864,7 @@ static void __exit dm_bufio_exit(void)
> > for (i = 0; i < ARRAY_SIZE(dm_bufio_caches); i++) {
> > struct kmem_cache *kc = dm_bufio_caches[i];
> >
> > - if (kc)
> > - kmem_cache_destroy(kc);
> > + kmem_cache_destroy(kc);
> > }
>
> The variable here can be NULL. I don't know how did you conclude that it
> cannot. It seems that you didn't test the patch, if you did, you'd hit
> NULL pointer dereference here.

kmem_cache_destroy(), mempool_destroy(), etc all check for NULL and just
return. So there is no need for the callers to check for NULL too.

Mike


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