linux-kernel - Re: linux-next: build warning after merge of the vfs-brauner tree

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Date: Wed, 6 Mar 2024 15:58:30 +1100
From: Stephen Rothwell <sfr@...b.auug.org.au>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christian Brauner <brauner@...nel.org>, Tong Tiangen
 <tongtiangen@...wei.com>, Linux Kernel Mailing List
 <linux-kernel@...r.kernel.org>, Linux Next Mailing List
 <linux-next@...r.kernel.org>
Subject: Re: linux-next: build warning after merge of the vfs-brauner tree

Hi all,

On Wed, 6 Mar 2024 15:37:03 +1100 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> On Tue, 5 Mar 2024 18:48:30 -0800 Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> >
> > On Tue, 5 Mar 2024 at 15:51, Stephen Rothwell <sfr@...b.auug.org.au> wrote:  
> > >
> > > fs/coredump.c: In function 'dump_user_range':
> > > fs/coredump.c:923:40: warning: left-hand operand of comma expression has no effect [-Wunused-value]
> > >   923 | #define dump_page_copy(src, dst) ((dst), (src))
> > >       |                                        ^
> > > fs/coredump.c:948:58: note: in expansion of macro 'dump_page_copy'
> > >   948 |                         int stop = !dump_emit_page(cprm, dump_page_copy(page, dump_page));
> > >       |                                                          ^~~~~~~~~~~~~~
> > >
> > > Introduced by commit
> > >
> > >   4630f2caafcd ("coredump: get machine check errors early rather than during iov_iter")    
> > 
> > Bah. If comes from that
> > 
> >   #define dump_page_copy(src,dst) ((dst),(src))
> > 
> > and I did it that way because I wanted to avoid *another* warning,
> > namely the "dst not used" thing.
> > 
> > But it would have probably been better to either make it an inline
> > function, or maybe an explicit cast, eg
> > 
> >   #define dump_page_copy(src,dst) ((void)(dst),(src))
> > 
> > or whatever.  
> 
> This became a build failure for my i386 defconfig build, so I did this:
> 
> From: Stephen Rothwell <sfr@...b.auug.org.au>
> Date: Wed, 6 Mar 2024 15:28:12 +1100
> Subject: [PATCH] fix up for "coredump: get machine check errors early rather
>  than during iov_iter"
> 
> Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
> ---
>  fs/coredump.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/coredump.c b/fs/coredump.c
> index ea155ffee14c..5353b7ac67f2 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -920,7 +920,10 @@ static struct page *dump_page_copy(struct page *src, struct page *dst)
>  
>  #define dump_page_alloc() ((struct page *)8) // Not NULL
>  #define dump_page_free(x) do { } while (0)
> -#define dump_page_copy(src, dst) ((dst), (src))
> +static struct page *dump_page_copy(struct page *src, struct page *dst)
> +{
> +        return NULL;
> +}
>  
>  #endif

On second thoughts I made it return "src" instead of "NULL";

-- 
Cheers,
Stephen Rothwell

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