[failures] mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch removed from -mm tree

[failures] mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch removed from -mm tree

[Andrew Morton]

The patch titled
     Subject: mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning
has been removed from the -mm tree.  Its filename was
     mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch

This patch was dropped because it had testing failures

------------------------------------------------------
From: Waiman Long <longman@redhat.com>
Subject: mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning

The gcc 12 compiler reports a "'mem_section' will never be NULL" warning
on the following code:

    static inline struct mem_section *__nr_to_section(unsigned long nr)
    {
    #ifdef CONFIG_SPARSEMEM_EXTREME
        if (!mem_section)
                return NULL;
    #endif
        if (!mem_section[SECTION_NR_TO_ROOT(nr)])
                return NULL;
       :

It happens with both CONFIG_SPARSEMEM_EXTREME on and off.  The mem_section
definition is

    #ifdef CONFIG_SPARSEMEM_EXTREME
    extern struct mem_section **mem_section;
    #else
    extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
    #endif

In the CONFIG_SPARSEMEM_EXTREME case, mem_section obviously cannot be
NULL, but *mem_section can be if memory hasn't been allocated for the
dynamic mem_section[] array yet.  In the !CONFIG_SPARSEMEM_EXTREME case,
mem_section is a static 2-dimensional array and so the check
"!mem_section[SECTION_NR_TO_ROOT(nr)]" doesn't make sense.

Fix this warning by checking for "!*mem_section" instead of "!mem_section"
and moving the "!mem_section[SECTION_NR_TO_ROOT(nr)]" check up inside the
CONFIG_SPARSEMEM_EXTREME block.

[longman@redhat.com: v2]
  Link: https://lkml.kernel.org/r/20220202003550.698768-1-longman@redhat.com
Link: https://lkml.kernel.org/r/20220201192924.672675-1-longman@redhat.com
Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
Fixes: 3e347261a80b ("sparsemem extreme implementation")
Signed-off-by: Waiman Long <longman@redhat.com>
Reported-by: Justin Forbes <jforbes@redhat.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Justin Forbes <jforbes@redhat.com>
Cc: Rafael Aquini <aquini@redhat.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Hector Martin <marcan@marcan.st>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mmzone.h |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/include/linux/mmzone.h~mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning
+++ a/include/linux/mmzone.h
@@ -1390,11 +1390,9 @@ static inline unsigned long *section_to_
 static inline struct mem_section *__nr_to_section(unsigned long nr)
 {
 #ifdef CONFIG_SPARSEMEM_EXTREME
-	if (!mem_section)
+	if (!*mem_section || !mem_section[SECTION_NR_TO_ROOT(nr)])
 		return NULL;
 #endif
-	if (!mem_section[SECTION_NR_TO_ROOT(nr)])
-		return NULL;
 	return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
 }
 extern size_t mem_section_usage_size(void);
_

Patches currently in -mm which might be from longman@redhat.com are

lib-vsprintf-avoid-redundant-work-with-0-size.patch
mm-page_owner-use-scnprintf-to-avoid-excessive-buffer-overrun-check.patch
mm-page_owner-print-memcg-information.patch
mm-page_owner-record-task-command-name.patch
ipc-mqueue-use-get_tree_nodev-in-mqueue_get_tree.patch

Re: [failures] mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch removed from -mm tree

[Waiman Long]

On 2/21/22 23:12, Andrew Morton wrote:
> The patch titled
>       Subject: mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning
> has been removed from the -mm tree.  Its filename was
>       mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning.patch
>
> This patch was dropped because it had testing failures
>
> ------------------------------------------------------
> From: Waiman Long <longman@redhat.com>
> Subject: mm/sparsemem: fix 'mem_section' will never be NULL gcc 12 warning
>
> The gcc 12 compiler reports a "'mem_section' will never be NULL" warning
> on the following code:
>
>      static inline struct mem_section *__nr_to_section(unsigned long nr)
>      {
>      #ifdef CONFIG_SPARSEMEM_EXTREME
>          if (!mem_section)
>                  return NULL;
>      #endif
>          if (!mem_section[SECTION_NR_TO_ROOT(nr)])
>                  return NULL;
>         :
>
> It happens with both CONFIG_SPARSEMEM_EXTREME on and off.  The mem_section
> definition is
>
>      #ifdef CONFIG_SPARSEMEM_EXTREME
>      extern struct mem_section **mem_section;
>      #else
>      extern struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT];
>      #endif
>
> In the CONFIG_SPARSEMEM_EXTREME case, mem_section obviously cannot be
> NULL, but *mem_section can be if memory hasn't been allocated for the
> dynamic mem_section[] array yet.  In the !CONFIG_SPARSEMEM_EXTREME case,
> mem_section is a static 2-dimensional array and so the check
> "!mem_section[SECTION_NR_TO_ROOT(nr)]" doesn't make sense.
>
> Fix this warning by checking for "!*mem_section" instead of "!mem_section"
> and moving the "!mem_section[SECTION_NR_TO_ROOT(nr)]" check up inside the
> CONFIG_SPARSEMEM_EXTREME block.
>
> [longman@redhat.com: v2]
>    Link: https://lkml.kernel.org/r/20220202003550.698768-1-longman@redhat.com
> Link: https://lkml.kernel.org/r/20220201192924.672675-1-longman@redhat.com
> Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y")
> Fixes: 3e347261a80b ("sparsemem extreme implementation")
> Signed-off-by: Waiman Long <longman@redhat.com>
> Reported-by: Justin Forbes <jforbes@redhat.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Justin Forbes <jforbes@redhat.com>
> Cc: Rafael Aquini <aquini@redhat.com>
> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
> Cc: Hector Martin <marcan@marcan.st>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
>   include/linux/mmzone.h |    4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
>
> --- a/include/linux/mmzone.h~mm-sparsemem-fix-mem_section-will-never-be-null-gcc-12-warning
> +++ a/include/linux/mmzone.h
> @@ -1390,11 +1390,9 @@ static inline unsigned long *section_to_
>   static inline struct mem_section *__nr_to_section(unsigned long nr)
>   {
>   #ifdef CONFIG_SPARSEMEM_EXTREME
> -	if (!mem_section)
> +	if (!*mem_section || !mem_section[SECTION_NR_TO_ROOT(nr)])
>   		return NULL;
>   #endif
> -	if (!mem_section[SECTION_NR_TO_ROOT(nr)])
> -		return NULL;
>   	return &mem_section[SECTION_NR_TO_ROOT(nr)][nr & SECTION_ROOT_MASK];
>   }
>   extern size_t mem_section_usage_size(void);

I am sorry that I had a brain fart on my part to add the "*" to 
mem_section. I will post an updated patch to fix that.

Cheers,
Longman