linux-kernel - Re: [PATCH v2] m68k: Define NR

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Message-ID: <aa23abe3-7236-4b9e-b237-3b822ac9d186@redhat.com>
Date: Tue, 24 Sep 2024 09:33:52 +0200
From: David Hildenbrand <david@...hat.com>
To: Guenter Roeck <linux@...ck-us.net>, linux-m68k@...ts.linux-m68k.org
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v2] m68k: Define NR_CPUS

On 24.09.24 01:56, Guenter Roeck wrote:
> SPLIT_PTE_PTLOCKS depends on "NR_CPUS >= 4". Unfortunately, that evaluates
> to true if there is no NR_CPUS configuration option. This results in
> CONFIG_SPLIT_PTE_PTLOCKS=y for mac_defconfig. This in turn causes the m68k
> "q800" and "virt" machines to crash in qemu if debugging options are
> enabled.
> 
> Making CONFIG_SPLIT_PTE_PTLOCKS dependent on the existence of NR_CPUS
> does not work since a dependency on the existence of a numeric Kconfig
> entry always evaluates to false. Example:
> 
> config HAVE_NO_NR_CPUS
>         def_bool y
>         depends on !NR_CPUS
> 
> After adding this to a Kconfig file, "make defconfig" includes:
> $ grep NR_CPUS .config
> CONFIG_NR_CPUS=64
> CONFIG_HAVE_NO_NR_CPUS=y
> 
> Define NR_CPUS for m68k instead to solve the problem.
> 
> Fixes: 394290cba966 ("mm: turn USE_SPLIT_PTE_PTLOCKS / USE_SPLIT_PTE_PTLOCKS into Kconfig options")
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Acked-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> v2: Instead of trying to make SPLIT_PTE_PTLOCKS depend on the
>      existence of NR_CPUS, define NR_CPUS for m68k.

Okay, looks like we're cleaning up CONFIG_NR_CPUS for good.

I'm back from conference travel tomorrow; I'll then throw in the following
into cross compilers and fixup any other arch that needs attention:


diff --git a/include/linux/threads.h b/include/linux/threads.h
index 1674a471b0b4..e31715e6746b 100644
--- a/include/linux/threads.h
+++ b/include/linux/threads.h
@@ -13,8 +13,7 @@
   * bit of memory.  Use nr_cpu_ids instead of this except for static bitmaps.
   */
  #ifndef CONFIG_NR_CPUS
-/* FIXME: This should be fixed in the arch's Kconfig */
-#define CONFIG_NR_CPUS 1
+#error "CONFIG_NR_CPUS not defined"
  #endif
  
  /* Places which use this should consider cpumask_var_t. */


-- 
Cheers,

David / dhildenb