Attachment 727765 Details for Bug 1039348

[patch] follow up fix

0002-mm-do-not-collapse-stack-gap-into-THP.patch (text/plain), 2.10 KB, created by Michal Hocko on 2017-06-06 08:06:40 UTC

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Creator: Michal Hocko

Created: 2017-06-06 08:06:40 UTC

Size: 2.10 KB

patch

obsolete

>From 0f608b435eeabb253cb0a65b5e6d27694a33af3e Mon Sep 17 00:00:00 2001
>From: Michal Hocko <mhocko@suse.com>
>Date: Thu, 25 May 2017 08:12:42 +0200
>Subject: [PATCH 2/2] mm: do not collapse stack gap into THP
>
>Oleg has noticed that khugepaged will happilly collapse stack vma (as
>long as it is not an early stack - see is_vma_temporary_stack) and
>it might effectively remove the stack gap area as well because a larger
>part of the stack vma is usually populated. The same applies to the
>page fault handler.
>
>Fix this by checking stack_guard_area when revalidating a VMA
>in hugepage_vma_revalidate.  We do not want to hook/replace
>is_vma_temporary_stack() check because THP might be still useful for
>stack, all we need is excluding the gap from collapsing into a THP.
>
>Also check the to-be-created THP in do_huge_pmd_anonymous_page to
>make sure it is completely outside of the gap area because we we could
>create THP covering the gap area.
>
>Noticed-by: Oleg Nesterov <oleg@redhat.com>
>Signed-off-by: Michal Hocko <mhocko@suse.com>
>---
> mm/huge_memory.c | 3 +++
> mm/khugepaged.c  | 4 ++++
> 2 files changed, 7 insertions(+)
>
>diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>index a84909cf20d3..a8b6881bb2a2 100644
>--- a/mm/huge_memory.c
>+++ b/mm/huge_memory.c
>@@ -664,6 +664,9 @@ int do_huge_pmd_anonymous_page(struct vm_fault *vmf)
> 
> 	if (haddr < vma->vm_start || haddr + HPAGE_PMD_SIZE > vma->vm_end)
> 		return VM_FAULT_FALLBACK;
>+	if (stack_guard_area(vma, haddr) ||
>+			stack_guard_area(vma, haddr + HPAGE_PMD_SIZE))
>+		return VM_FAULT_FALLBACK;
> 	if (unlikely(anon_vma_prepare(vma)))
> 		return VM_FAULT_OOM;
> 	if (unlikely(khugepaged_enter(vma, vma->vm_flags)))
>diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>index 7cb9c88bb4a3..ce29e5cc7809 100644
>--- a/mm/khugepaged.c
>+++ b/mm/khugepaged.c
>@@ -859,6 +859,10 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
> 		return SCAN_ADDRESS_RANGE;
> 	if (!hugepage_vma_check(vma))
> 		return SCAN_VMA_CHECK;
>+
>+	/* never try to collapse stack gap */
>+	if (stack_guard_area(vma, hstart) || stack_guard_area(vma, hend))
>+		return SCAN_ADDRESS_RANGE;
> 	return 0;
> }
> 
>-- 
>2.11.0
>

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