Patch "mm: pmd dirty emulation in page fault handler" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mm: pmd dirty emulation in page fault handler

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mm-pmd-dirty-emulation-in-page-fault-handler.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 20f664aabeb88d582b623a625f83b0454fa34f07 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Tue, 10 Jan 2017 16:57:51 -0800
Subject: mm: pmd dirty emulation in page fault handler

From: Minchan Kim <minchan@kernel.org>

commit 20f664aabeb88d582b623a625f83b0454fa34f07 upstream.

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 currently page fault handler doesn't supports dirty bit
emulation of pmd for non-HW dirty-bit architecture so that application
stucks until VM marked the pmd dirty.

How the emulation work depends on the architecture.  In case of arm64,
when it set up pte firstly, it sets pte PTE_RDONLY to get a chance to
mark the pte dirty via triggering page fault when store access happens.
Once the page fault occurs, VM marks the pmd dirty and arch code for
setting pmd will clear PTE_RDONLY for application to proceed.

IOW, if VM doesn't mark the pmd dirty, application hangs forever by
repeated fault(i.e., store op but the pmd is PTE_RDONLY).

This patch enables pmd dirty-bit emulation for those architectures.

[1] b8d3c4c3009d, mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called

Fixes: b8d3c4c3009d ("mm/huge_memory.c: don't split THP page when MADV_FREE syscall is called")
Link: http://lkml.kernel.org/r/1482506098-6149-1-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Andreas Schwab <schwab@suse.de>
Tested-by: Andreas Schwab <schwab@suse.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jason Evans <je@fb.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/huge_memory.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -872,15 +872,17 @@ void huge_pmd_set_accessed(struct fault_
 {
 	pmd_t entry;
 	unsigned long haddr;
+	bool write = fe->flags & FAULT_FLAG_WRITE;
 
 	fe->ptl = pmd_lock(fe->vma->vm_mm, fe->pmd);
 	if (unlikely(!pmd_same(*fe->pmd, orig_pmd)))
 		goto unlock;
 
 	entry = pmd_mkyoung(orig_pmd);
+	if (write)
+		entry = pmd_mkdirty(entry);
 	haddr = fe->address & HPAGE_PMD_MASK;
-	if (pmdp_set_access_flags(fe->vma, haddr, fe->pmd, entry,
-				fe->flags & FAULT_FLAG_WRITE))
+	if (pmdp_set_access_flags(fe->vma, haddr, fe->pmd, entry, write))
 		update_mmu_cache_pmd(fe->vma, fe->address, fe->pmd);
 
 unlock:


Patches currently in stable-queue which might be from minchan@kernel.org are

queue-4.9/zram-support-bdi_cap_stable_writes.patch
queue-4.9/zram-revalidate-disk-under-init_lock.patch
queue-4.9/mm-pmd-dirty-emulation-in-page-fault-handler.patch