Commit 838d0235 authored by Qi Zheng's avatar Qi Zheng Committed by Andrew Morton
Browse files

mm: mremap: move_ptes() use pte_offset_map_rw_nolock() 

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: default avatarQi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: default avatarMuchun 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 24553a97

mm/mremap.c

+10 −1
Original line number Diff line number Diff line
@@ -140,6 +140,7 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, 
{

	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_struct *vma, pmd_t *old_pmd, 
		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;