Commit ca120cf6 authored Sep 03, 2016 by Dan Williams

mm: fix show_smap() for zone_device-pmd ranges



Attempting to dump /proc/<pid>/smaps for a process with pmd dax mappings
currently results in the following VM_BUG_ONs:

 kernel BUG at mm/huge_memory.c:1105!
 task: ffff88045f16b140 task.stack: ffff88045be14000
 RIP: 0010:[<ffffffff81268f9b>]  [<ffffffff81268f9b>] follow_trans_huge_pmd+0x2cb/0x340
 [..]
 Call Trace:
  [<ffffffff81306030>] smaps_pte_range+0xa0/0x4b0
  [<ffffffff814c2755>] ? vsnprintf+0x255/0x4c0
  [<ffffffff8123c46e>] __walk_page_range+0x1fe/0x4d0
  [<ffffffff8123c8a2>] walk_page_vma+0x62/0x80
  [<ffffffff81307656>] show_smap+0xa6/0x2b0

 kernel BUG at fs/proc/task_mmu.c:585!
 RIP: 0010:[<ffffffff81306469>]  [<ffffffff81306469>] smaps_pte_range+0x499/0x4b0
 Call Trace:
  [<ffffffff814c2795>] ? vsnprintf+0x255/0x4c0
  [<ffffffff8123c46e>] __walk_page_range+0x1fe/0x4d0
  [<ffffffff8123c8a2>] walk_page_vma+0x62/0x80
  [<ffffffff81307696>] show_smap+0xa6/0x2b0

These locations are sanity checking page flags that must be set for an
anonymous transparent huge page, but are not set for the zone_device
pages associated with dax mappings.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

parent 4c3cb6e9

fs/proc/task_mmu.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -581,6 +581,8 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
		mss->anonymous_thp += HPAGE_PMD_SIZE;
		else if (PageSwapBacked(page))
		mss->shmem_thp += HPAGE_PMD_SIZE;
		else if (is_zone_device_page(page))
		/* pass */;
		else
		VM_BUG_ON_PAGE(1, page);
		smaps_account(mss, page, true, pmd_young(pmd), pmd_dirty(pmd));

mm/huge_memory.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1078,7 +1078,7 @@ struct page follow_trans_huge_pmd(struct vm_area_struct vma,
		goto out;

		page = pmd_page(*pmd);
		VM_BUG_ON_PAGE(!PageHead(page), page);
		VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page);
		if (flags & FOLL_TOUCH)
		touch_pmd(vma, addr, pmd);
		if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
		@@ -1116,7 +1116,7 @@ struct page follow_trans_huge_pmd(struct vm_area_struct vma,
		}
		skip_mlock:
		page += (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT;
		VM_BUG_ON_PAGE(!PageCompound(page), page);
		VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page);
		if (flags & FOLL_GET)
		get_page(page);

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