Re: [PATCH] mm: Fix clang W=1 compiler warnings

[Jakub Kicinski <kuba@kernel.org>]

On Fri, 7 Feb 2025 17:01:00 -0800 Linus Torvalds wrote:
> On Fri, 7 Feb 2025 at 16:49, Jakub Kicinski <kuba@kernel.org> wrote:
> > Could we possibly please still consider taking this in for 6.14? :(
> > Since the warning comes from vmstat.h pretty much every object file
> > generates this warning. clang 19 is getting more widely used now,
> > its making it hard to see new warnings.  
> 
> So:
> 
>  - I build the kernel with clang, but I don't have clang-19, so it's
> kind of pointless sending patches that DO NOT EVEN EXPLAIN WHAT THE
> WARNINGS ARE.
> 
>  - and even if you explain *WHAT* the warnings are, please also
> explain *WHY* they are valid and should be cared about.
> 
> Because honestly, W=1 is literally meant for "warnings that aren't
> necessarily valid". That's why they aren't on by default.
> 
> So no, I'm certainly not applying unexplained random patches that
> don't bother to explain the what or the why. Not for 6.14, not ever.

I thought I'd ask.. :) FWIW this for every single object:

  CC      net/core/request_sock.o
In file included from ../net/core/request_sock.c:14:
In file included from ../include/linux/tcp.h:17:
In file included from ../include/linux/skbuff.h:17:
In file included from ../include/linux/bvec.h:10:
In file included from ../include/linux/highmem.h:8:
In file included from ../include/linux/cacheflush.h:5:
In file included from ../arch/x86/include/asm/cacheflush.h:5:
In file included from ../include/linux/mm.h:2224:
../include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
  504 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
      |                            ~~~~~~~~~~~~~~~~~~~~~ ^
  505 |                            item];
      |                            ~~~~
../include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
  511 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
      |                            ~~~~~~~~~~~~~~~~~~~~~ ^
  512 |                            NR_VM_NUMA_EVENT_ITEMS +
      |                            ~~~~~~~~~~~~~~~~~~~~~~
../include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
  524 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
      |                            ~~~~~~~~~~~~~~~~~~~~~ ^
  525 |                            NR_VM_NUMA_EVENT_ITEMS +
      |                            ~~~~~~~~~~~~~~~~~~~~~~
3 warnings generated.

> Fix the patch. Explain the problem. And possibly just disable the warning.

That'd be great. Nathan, would that be okay with you?