The patch titled
Subject: mm: page_mkclean vs MADV_DONTNEED race
has been added to the -mm tree. Its filename is
mm-page_mkclean-vs-madv_dontneed-race.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_mkclean-vs-madv_dontneed-race.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_mkclean-vs-madv_dontneed-race.patch
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------------------------------------------------------
From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
Subject: mm: page_mkclean vs MADV_DONTNEED race
MADV_DONTNEED is handled with mmap_sem taken in read mode. We call
page_mkclean without holding mmap_sem.
MADV_DONTNEED implies that pages in the region are unmapped and subsequent
access to the pages in that range is handled as a new page fault. This
implies that if we don't have parallel access to the region when
MADV_DONTNEED is run we expect those range to be unallocated.
w.r.t page_mkclean we need to make sure that we don't break the
MADV_DONTNEED semantics. MADV_DONTNEED check for pmd_none without holding
pmd_lock. This implies we skip the pmd if we temporarily mark pmd none.
Avoid doing that while marking the page clean.
Keep the sequence same for dax too even though we don't support
MADV_DONTNEED for dax mapping
Link: http://lkml.kernel.org/r/20190321040610.14226-1-aneesh.kumar@xxxxxxxxxxxxx
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc:"Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 2 +-
mm/rmap.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
--- a/fs/dax.c~mm-page_mkclean-vs-madv_dontneed-race
+++ a/fs/dax.c
@@ -813,7 +813,7 @@ static void dax_entry_mkclean(struct add
goto unlock_pmd;
flush_cache_page(vma, address, pfn);
- pmd = pmdp_huge_clear_flush(vma, address, pmdp);
+ pmd = pmdp_invalidate(vma, address, pmdp);
pmd = pmd_wrprotect(pmd);
pmd = pmd_mkclean(pmd);
set_pmd_at(vma->vm_mm, address, pmdp, pmd);
--- a/mm/rmap.c~mm-page_mkclean-vs-madv_dontneed-race
+++ a/mm/rmap.c
@@ -928,7 +928,7 @@ static bool page_mkclean_one(struct page
continue;
flush_cache_page(vma, address, page_to_pfn(page));
- entry = pmdp_huge_clear_flush(vma, address, pmd);
+ entry = pmdp_invalidate(vma, address, pmd);
entry = pmd_wrprotect(entry);
entry = pmd_mkclean(entry);
set_pmd_at(vma->vm_mm, address, pmd, entry);
_
Patches currently in -mm which might be from aneesh.kumar@xxxxxxxxxxxxx are
mm-page_mkclean-vs-madv_dontneed-race.patch
