[PATCH 3/5] mm: fix show_smap() for zone_device-pmd ranges

Dan Williams
2016-09-06T16:52:42Z

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>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
fs/proc/task_mmu.c | 2 ++
mm/huge_memory.c | 4 ++--
2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 187d84ef9de9..f6fa99eca515 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -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));
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2db2112aa31e..a6abd76baa72 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -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);