Commit a5be621e authored by Hugh Dickins's avatar Hugh Dickins Committed by Andrew Morton
Browse files

mm/mremap: retry if either pte_offset_map_*lock() fails 

move_ptes() return -EAGAIN if pte_offset_map_lock() of old fails, or if
pte_offset_map_nolock() of new fails: move_page_tables() retry if so.

But that does need a pmd_none() check inside, to stop endless loop when
huge shmem is truncated (thank you to syzbot); and move_huge_pmd() must
tolerate that a page table might have been allocated there just before (of
course it would be more satisfying to remove the empty page table, but
this is not a path worth optimizing).

Link: https://lkml.kernel.org/r/65e5e84a-f04-947-23f2-b97d3462e1e@google.com


Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 670ddd8c

mm/huge_memory.c

+3 −2
Original line number Diff line number Diff line
@@ -1760,9 +1760,10 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr, 


	/*

	 * The destination pmd shouldn't be established, free_pgtables()

	 * should have release it.

	 * should have released it; but move_page_tables() might have already

	 * inserted a page table, if racing against shmem/file collapse.

	 */

	if (WARN_ON(!pmd_none(*new_pmd))) {

	if (!pmd_none(*new_pmd)) {

		VM_BUG_ON(pmd_trans_huge(*new_pmd));

		return false;

	}

mm/mremap.c

+20 −8
Original line number Diff line number Diff line
@@ -133,7 +133,7 @@ static pte_t move_soft_dirty_pte(pte_t pte) 
	return pte;

}



static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,

static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,

		unsigned long old_addr, unsigned long old_end,

		struct vm_area_struct *new_vma, pmd_t *new_pmd,

		unsigned long new_addr, bool need_rmap_locks)
@@ -143,6 +143,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, 
	spinlock_t *old_ptl, *new_ptl;

	bool force_flush = false;

	unsigned long len = old_end - old_addr;

	int err = 0;



	/*

	 * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
@@ -170,8 +171,16 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, 
	 * pte locks because exclusive mmap_lock prevents deadlock.

	 */

	old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);

	new_pte = pte_offset_map(new_pmd, new_addr);

	new_ptl = pte_lockptr(mm, new_pmd);

	if (!old_pte) {

		err = -EAGAIN;

		goto out;

	}

	new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl);

	if (!new_pte) {

		pte_unmap_unlock(old_pte, old_ptl);

		err = -EAGAIN;

		goto out;

	}

	if (new_ptl != old_ptl)

		spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);

	flush_tlb_batched_pending(vma->vm_mm);
@@ -208,8 +217,10 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, 
		spin_unlock(new_ptl);

	pte_unmap(new_pte - 1);

	pte_unmap_unlock(old_pte - 1, old_ptl);

out:

	if (need_rmap_locks)

		drop_rmap_locks(vma);

	return err;

}



#ifndef arch_supports_page_table_move
@@ -537,6 +548,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma, 
		new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);

		if (!new_pmd)

			break;

again:

		if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) ||

		    pmd_devmap(*old_pmd)) {

			if (extent == HPAGE_PMD_SIZE &&
@@ -544,8 +556,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma, 
					   old_pmd, new_pmd, need_rmap_locks))

				continue;

			split_huge_pmd(vma, old_pmd, old_addr);

			if (pmd_trans_unstable(old_pmd))

				continue;

		} else if (IS_ENABLED(CONFIG_HAVE_MOVE_PMD) &&

			   extent == PMD_SIZE) {

			/*
@@ -556,11 +566,13 @@ unsigned long move_page_tables(struct vm_area_struct *vma, 
					   old_pmd, new_pmd, true))

				continue;

		}



		if (pmd_none(*old_pmd))

			continue;

		if (pte_alloc(new_vma->vm_mm, new_pmd))

			break;

		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,

			  new_pmd, new_addr, need_rmap_locks);

		if (move_ptes(vma, old_pmd, old_addr, old_addr + extent,

			      new_vma, new_pmd, new_addr, need_rmap_locks) < 0)

			goto again;

	}



	mmu_notifier_invalidate_range_end(&range);