[merged mm-stable] mm-mremap-move_ptes-use-pte_offset_map_rw_nolock.patch removed from -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The quilt patch titled
     Subject: mm: mremap: move_ptes() use pte_offset_map_rw_nolock()
has been removed from the -mm tree.  Its filename was
     mm-mremap-move_ptes-use-pte_offset_map_rw_nolock.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Qi Zheng <zhengqi.arch@bytedance.com>
Subject: mm: mremap: move_ptes() use pte_offset_map_rw_nolock()
Date: Thu, 26 Sep 2024 14:46:22 +0800

In move_ptes(), we may modify the new_pte after acquiring the new_ptl, so
convert it to using pte_offset_map_rw_nolock().  Now new_pte is none, so
hpage_collapse_scan_file() path can not find this by traversing
file->f_mapping, so there is no concurrency with retract_page_tables(). 
In addition, we already hold the exclusive mmap_lock, so this new_pte page
is stable, so there is no need to get pmdval and do pmd_same() check.

Link: https://lkml.kernel.org/r/9d582a09dbcf12e562ac5fe0ba05e9248a58f5e0.1727332572.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mremap.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/mm/mremap.c~mm-mremap-move_ptes-use-pte_offset_map_rw_nolock
+++ a/mm/mremap.c
@@ -140,6 +140,7 @@ static int move_ptes(struct vm_area_stru
 {
 	struct mm_struct *mm = vma->vm_mm;
 	pte_t *old_pte, *new_pte, pte;
+	pmd_t dummy_pmdval;
 	spinlock_t *old_ptl, *new_ptl;
 	bool force_flush = false;
 	unsigned long len = old_end - old_addr;
@@ -175,7 +176,15 @@ static int move_ptes(struct vm_area_stru
 		err = -EAGAIN;
 		goto out;
 	}
-	new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl);
+	/*
+	 * Now new_pte is none, so hpage_collapse_scan_file() path can not find
+	 * this by traversing file->f_mapping, so there is no concurrency with
+	 * retract_page_tables(). In addition, we already hold the exclusive
+	 * mmap_lock, so this new_pte page is stable, so there is no need to get
+	 * pmdval and do pmd_same() check.
+	 */
+	new_pte = pte_offset_map_rw_nolock(mm, new_pmd, new_addr, &dummy_pmdval,
+					   &new_ptl);
 	if (!new_pte) {
 		pte_unmap_unlock(old_pte, old_ptl);
 		err = -EAGAIN;
_

Patches currently in -mm which might be from zhengqi.arch@bytedance.com are