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Date: Thu, 4 Apr 2024 18:28:43 -0400
From: Kent Overstreet <kent.overstreet@linux.dev>
To: Suren Baghdasaryan <surenb@google.com>
Cc: Matthew Wilcox <willy@infradead.org>, akpm@linux-foundation.org, 
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Subject: Re: [PATCH 1/1] mm: change inlined allocation helpers to account at
 the call site
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On Thu, Apr 04, 2024 at 03:17:43PM -0700, Suren Baghdasaryan wrote:
> On Thu, Apr 4, 2024 at 10:08 AM Suren Baghdasaryan <surenb@google.com> wrote:
> >
> > On Thu, Apr 4, 2024 at 10:04 AM Matthew Wilcox <willy@infradead.org> 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 = 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)?

Correct, it's not hiding bugs in this case, it's adding type safety.

checkpatch is definitely not authoritative, you really have to use your
own judgement with it