Commit 01871e59 authored Jan 15, 2016 by Ross Zwisler Committed by Linus Torvalds Jan 15, 2016

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 <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reported-by: Jeff Moyer <jmoyer@redhat.com>
Reported-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b2e0d162

mm/huge_memory.c

+6 −8

Original line number	Diff line number	Diff line
		@@ -938,7 +938,6 @@ 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));
		@@ -946,7 +945,6 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
		}
		set_pmd_at(mm, addr, pmd, entry);
		update_mmu_cache_pmd(vma, addr, pmd);
		}
		spin_unlock(ptl);
		}