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From: Suren Baghdasaryan <surenb@google.com>
Date: Thu, 4 Apr 2024 15:17:43 -0700
Message-ID: <CAJuCfpHy5Xo76S7h9rEuA3cQ1pVqurL=wmtQ2cx9-xN1aa_C_A@mail.gmail.com>
Subject: Re: [PATCH 1/1] mm: change inlined allocation helpers to account at
 the call site
To: Matthew Wilcox <willy@infradead.org>
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On Thu, Apr 4, 2024 at 10:08=E2=80=AFAM Suren Baghdasaryan <surenb@google.c=
om> wrote:
>
> On Thu, Apr 4, 2024 at 10:04=E2=80=AFAM Matthew Wilcox <willy@infradead.o=
rg> wrote:
> >
> > On Thu, Apr 04, 2024 at 09:54:04AM -0700, Suren Baghdasaryan wrote:
> > > +++ b/include/linux/dma-fence-chain.h
> > > @@ -86,10 +86,7 @@ dma_fence_chain_contained(struct dma_fence *fence)
> > >   *
> > >   * Returns a new struct dma_fence_chain object or NULL on failure.
> > >   */
> > > -static inline struct dma_fence_chain *dma_fence_chain_alloc(void)
> > > -{
> > > -     return kmalloc(sizeof(struct dma_fence_chain), GFP_KERNEL);
> > > -};
> > > +#define dma_fence_chain_alloc()      kmalloc(sizeof(struct dma_fence=
_chain), GFP_KERNEL)
> >
> > You've removed some typesafety here.  Before, if I wrote:
> >
> >         struct page *page =3D dma_fence_chain_alloc();
> >
> > the compiler would warn me that I've done something stupid.  Now it
> > can't tell.  Suggest perhaps:
> >
> > #define dma_fence_chain_alloc()                                        =
   \
> >         (struct dma_fence_chain *)kmalloc(sizeof(struct dma_fence_chain=
), \
> >                                                 GFP_KERNEL)
> >
> > but maybe there's a better way of doing that.  There are a few other
> > occurrences of the same problem in this monster patch.
>
> Got your point.

Ironically, checkpatch generates warnings for these type casts:

WARNING: unnecessary cast may hide bugs, see
http://c-faq.com/malloc/mallocnocast.html
#425: FILE: include/linux/dma-fence-chain.h:90:
+ ((struct dma_fence_chain *)kmalloc(sizeof(struct dma_fence_chain),
GFP_KERNEL))

I guess I can safely ignore them in this case (since we cast to the
expected type)?

>
> >
> > > +++ b/include/linux/hid_bpf.h
> > > @@ -149,10 +149,7 @@ static inline int hid_bpf_connect_device(struct =
hid_device *hdev) { return 0; }
> > >  static inline void hid_bpf_disconnect_device(struct hid_device *hdev=
) {}
> > >  static inline void hid_bpf_destroy_device(struct hid_device *hid) {}
> > >  static inline void hid_bpf_device_init(struct hid_device *hid) {}
> > > -static inline u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, =
u8 *rdesc, unsigned int *size)
> > > -{
> > > -     return kmemdup(rdesc, *size, GFP_KERNEL);
> > > -}
> > > +#define call_hid_bpf_rdesc_fixup(_hdev, _rdesc, _size) kmemdup(_rdes=
c, *(_size), GFP_KERNEL)
> >
> > here
> >
> > > -static inline handle_t *jbd2_alloc_handle(gfp_t gfp_flags)
> > > -{
> > > -     return kmem_cache_zalloc(jbd2_handle_cache, gfp_flags);
> > > -}
> > > +#define jbd2_alloc_handle(_gfp_flags)        kmem_cache_zalloc(jbd2_=
handle_cache, _gfp_flags)
> >
> > here
> >
> > > +++ b/include/linux/skmsg.h
> > > @@ -410,11 +410,8 @@ void sk_psock_stop_verdict(struct sock *sk, stru=
ct sk_psock *psock);
> > >  int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock,
> > >                        struct sk_msg *msg);
> > >
> > > -static inline struct sk_psock_link *sk_psock_init_link(void)
> > > -{
> > > -     return kzalloc(sizeof(struct sk_psock_link),
> > > -                    GFP_ATOMIC | __GFP_NOWARN);
> > > -}
> > > +#define sk_psock_init_link() \
> > > +             kzalloc(sizeof(struct sk_psock_link), GFP_ATOMIC | __GF=
P_NOWARN)
> >
> > here
> >
> > ... I kind of gave up at this point.  You'll want to audit for yourself
> > anyway ;-)
>
> Yes, I'll go over it and will make the required changes. Thanks for
> looking into it!
> Suren.