From 01871e59af5cc1cbf290ad6b4b95cd2f0cec9e8c Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Fri, 15 Jan 2016 16:56:02 -0800 Subject: [PATCH] mm, dax: fix livelock, allow dax pmd mappings to become writeable Prior to this change DAX PMD mappings that were made read-only were never able to be made writable again. This is because the code in insert_pfn_pmd() that calls pmd_mkdirty() and pmd_mkwrite() would skip these calls if the PMD already existed in the page table. Instead, if we are doing a write always mark the PMD entry as dirty and writeable. Without this code we can get into a condition where we mark the PMD as read-only, and then on a subsequent write fault we get into an infinite loop of PMD faults where we try unsuccessfully to make the PMD writeable. Signed-off-by: Ross Zwisler Signed-off-by: Dan Williams Reported-by: Jeff Moyer Reported-by: Toshi Kani Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/huge_memory.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9d12d63a0ddd..996e86dbeb43 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -938,15 +938,13 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, spinlock_t *ptl; ptl = pmd_lock(mm, pmd); - if (pmd_none(*pmd)) { - entry = pmd_mkhuge(pfn_pmd(pfn, prot)); - if (write) { - entry = pmd_mkyoung(pmd_mkdirty(entry)); - entry = maybe_pmd_mkwrite(entry, vma); - } - set_pmd_at(mm, addr, pmd, entry); - update_mmu_cache_pmd(vma, addr, pmd); + entry = pmd_mkhuge(pfn_pmd(pfn, prot)); + if (write) { + entry = pmd_mkyoung(pmd_mkdirty(entry)); + entry = maybe_pmd_mkwrite(entry, vma); } + set_pmd_at(mm, addr, pmd, entry); + update_mmu_cache_pmd(vma, addr, pmd); spin_unlock(ptl); } -- 2.20.1