[PATCH] mm: pmd dirty emulation in page fault handler

[Minchan Kim]

Andreas reported [1] made a test in jemalloc hang in THP mode in arm64.
http://lkml.kernel.org/r/mvmmvfy37g1.fsf@hawking.suse.de

The problem is page fault handler supports only accessed flag emulation
for THP page of SW-dirty/accessed architecture.

This patch enables dirty-bit emulation for those architectures.
Without it, MADV_FREE makes application hang by repeated fault forever.

[1] mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called

Cc: Jason Evans <je at fb.com>
Cc: Kirill A. Shutemov <kirill.shutemov at linux.intel.com>
Cc: Will Deacon <will.deacon at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: linux-arch at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Cc: <stable at vger.kernel.org> [4.5+]
Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called")
Reported-by: Andreas Schwab <schwab at suse.de>
Signed-off-by: Minchan Kim <minchan at kernel.org>
---
 mm/huge_memory.c |  6 ++++--
 mm/memory.c      | 18 ++++++++++--------
 2 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 10eedbf..29ec8a4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -883,15 +883,17 @@ void huge_pmd_set_accessed(struct vm_fault *vmf, pmd_t orig_pmd)
 {
 	pmd_t entry;
 	unsigned long haddr;
+	bool write = vmf->flags & FAULT_FLAG_WRITE;
 
 	vmf->ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
 	if (unlikely(!pmd_same(*vmf->pmd, orig_pmd)))
 		goto unlock;
 
 	entry = pmd_mkyoung(orig_pmd);
+	if (write)
+		entry = pmd_mkdirty(entry);
 	haddr = vmf->address & HPAGE_PMD_MASK;
-	if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry,
-				vmf->flags & FAULT_FLAG_WRITE))
+	if (pmdp_set_access_flags(vmf->vma, haddr, vmf->pmd, entry, write))
 		update_mmu_cache_pmd(vmf->vma, vmf->address, vmf->pmd);
 
 unlock:
diff --git a/mm/memory.c b/mm/memory.c
index 36c774f..7408ddc 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3637,18 +3637,20 @@ static int __handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
 			if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
 				return do_huge_pmd_numa_page(&vmf, orig_pmd);
 
-			if ((vmf.flags & FAULT_FLAG_WRITE) &&
-					!pmd_write(orig_pmd)) {
-				ret = wp_huge_pmd(&vmf, orig_pmd);
-				if (!(ret & VM_FAULT_FALLBACK))
+			if (vmf.flags & FAULT_FLAG_WRITE) {
+				if (!pmd_write(orig_pmd)) {
+					ret = wp_huge_pmd(&vmf, orig_pmd);
+					if (ret == VM_FAULT_FALLBACK)
+						goto pte_fault;
 					return ret;
-			} else {
-				huge_pmd_set_accessed(&vmf, orig_pmd);
-				return 0;
+				}
 			}
+
+			huge_pmd_set_accessed(&vmf, orig_pmd);
+			return 0;
 		}
 	}
-
+pte_fault:
 	return handle_pte_fault(&vmf);
 }
 
-- 
2.7.4