Re: + mm-hugetlb-initialize-page-to-null-in-alloc_buddy_huge_page_with_mpol.patch added to -mm tree

[Nathan Chancellor <nathan@kernel.org>]

Andrew,

On 8/10/2021 6:18 PM, akpm@linux-foundation.org wrote:
> The patch titled
>       Subject: mm/hugetlb: Initialize page to NULL in alloc_buddy_huge_page_with_mpol()
> has been added to the -mm tree.  Its filename is
>       mm-hugetlb-initialize-page-to-null-in-alloc_buddy_huge_page_with_mpol.patch
> 
> This patch should soon appear at
>      https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-initialize-page-to-null-in-alloc_buddy_huge_page_with_mpol.patch
> and later at
>      https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-initialize-page-to-null-in-alloc_buddy_huge_page_with_mpol.patch
> 
> Before you just go and hit "reply", please:
>     a) Consider who else should be cc'ed
>     b) Prefer to cc a suitable mailing list as well
>     c) Ideally: find the original patch on the mailing list and do a
>        reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
> 
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
> 
> ------------------------------------------------------
> From: Nathan Chancellor <nathan@kernel.org>
> Subject: mm/hugetlb: Initialize page to NULL in alloc_buddy_huge_page_with_mpol()
> 
> Clang warns:
> 
> mm/hugetlb.c:2162:6: warning: variable 'page' is used uninitialized
> whenever 'if' condition is false [-Wsometimes-uninitialized]
>          if (mpol_is_preferred_many(mpol)) {
>              ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/hugetlb.c:2172:7: note: uninitialized use occurs here
>          if (!page)
>               ^~~~
> mm/hugetlb.c:2162:2: note: remove the 'if' if its condition is always
> true
>          if (mpol_is_preferred_many(mpol)) {
>          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> mm/hugetlb.c:2155:19: note: initialize the variable 'page' to silence
> this warning
>          struct page *page;
>                           ^
>                            = NULL
> 1 warning generated.
> 
> Initialize page to NULL like in dequeue_huge_page_vma() so that page is
> not used uninitialized.
> 
> Link: https://lkml.kernel.org/r/20210810200632.3812797-1-nathan@kernel.org
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Feng Tang <feng.tang@intel.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>   mm/hugetlb.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/hugetlb.c~mm-hugetlb-initialize-page-to-null-in-alloc_buddy_huge_page_with_mpol
> +++ a/mm/hugetlb.c
> @@ -2088,7 +2088,7 @@ static
>   struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
>   		struct vm_area_struct *vma, unsigned long addr)
>   {
> -	struct page *page;
> +	struct page *page = NULL;
>   	struct mempolicy *mpol;
>   	gfp_t gfp_mask = htlb_alloc_mask(h);
>   	int nid;
> _
> 
> Patches currently in -mm which might be from nathan@kernel.org are
> 
> mm-hugetlb-initialize-page-to-null-in-alloc_buddy_huge_page_with_mpol.patch
> 

Sorry for not making it clearer with a fixes tag but I did not intend 
for this to be a standalone patch but rather a fixup patch for 
mm-hugetlb-add-support-for-mempolicy-mpol_preferred_many-fix.patch, 
which fails to initialize page in alloc_buddy_huge_page_with_mpol(). I 
thought that replying inline to the thread would be enough.

Cheers,
Nathan