linux-kernel - Re: [PATCH 3/3] mm/mmap: Regression fix for unmapped_area{

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Date:   Fri, 14 Apr 2023 16:27:15 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "Liam.Howlett@...cle.com" <Liam.Howlett@...cle.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] mm/mmap: Regression fix for unmapped_area{_topdown}

On Fri, 2023-04-14 at 10:57 -0400, Liam R. Howlett wrote:<br>
> +       tmp = mas_next(&mas, ULONG_MAX);
> +       if (tmp && (tmp->vm_flags & VM_GROWSDOWN)) {

Why also check VM_GROWSDOWN here (and VM_GROWSUP below)?
vm_start/end_gap() already have checks inside.

> +               if (vm_start_gap(tmp) < gap + length - 1) {
> +                       low_limit = tmp->vm_end;
> +                       mas_reset(&mas);
> +                       goto retry;
> +               }
> +       } else {
> +               tmp = mas_prev(&mas, 0);
> +               if (tmp && (tmp->vm_flags & VM_GROWSUP) &&
> +                   vm_end_gap(tmp) > gap) {
> +                       low_limit = vm_end_gap(tmp); 
> +                       mas_reset(&mas);
> +                       goto retry; 
> +               }
> +       } 
> +

Could it be like this?

tmp = mas_next(&mas, ULONG_MAX);
if (tmp && vm_start_gap(tmp) < gap + length - 1) {
		low_limit = tmp->vm_end;
		mas_reset(&mas);
		goto retry;
	}
} else {
	tmp = mas_prev(&mas, 0);
	if (tmp && vm_end_gap(tmp) > gap) {
		low_limit = vm_end_gap(tmp);
		mas_reset(&mas);
		goto retry;
	}
}