[ Upstream commit 024eee0e83f0df52317be607ca521e0fc572aa07 ]
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
The bug was noticed by code review and I didn't observe any failures w.r.t test run. This is similar to
commit 58ceeb6bec86d9140f9d91d71a710e963523d063 Author: Kirill A. Shutemov kirill.shutemov@linux.intel.com Date: Thu Apr 13 14:56:26 2017 -0700
thp: fix MADV_DONTNEED vs. MADV_FREE race
commit ced108037c2aa542b3ed8b7afd1576064ad1362a Author: Kirill A. Shutemov kirill.shutemov@linux.intel.com Date: Thu Apr 13 14:56:20 2017 -0700
thp: fix MADV_DONTNEED vs. numa balancing race
Link: http://lkml.kernel.org/r/20190321040610.14226-1-aneesh.kumar@linux.ibm.com Signed-off-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Dan Williams dan.j.williams@intel.com Cc:"Kirill A . Shutemov" kirill@shutemov.name Cc: Andrea Arcangeli aarcange@redhat.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/dax.c | 2 +- mm/rmap.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c index 004c8ac1117c..75a289c31c7e 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -908,7 +908,7 @@ static void dax_mapping_entry_mkclean(struct address_space *mapping, 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); diff --git a/mm/rmap.c b/mm/rmap.c index 85b7f9423352..f048c2651954 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -926,7 +926,7 @@ static bool page_mkclean_one(struct page *page, struct vm_area_struct *vma, 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);