mm/huge_memory: remove stale locking logic from __split_huge_pmd()

Let's remove the stale logic that was required for reuse_swap_page().

[akpm@linux-foundation.org: simplification, per Yang Shi]

Link: https://lkml.kernel.org/r/20220131162940.210846-10-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cc580d9..2fe3821 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2133,8 +2133,6 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 {
        spinlock_t *ptl;
        struct mmu_notifier_range range;
-       bool do_unlock_folio = false;
-       pmd_t _pmd;
 
        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
                                address & HPAGE_PMD_MASK,
@@ -2153,42 +2151,12 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
                        goto out;
        }
 
-repeat:
-       if (pmd_trans_huge(*pmd)) {
-               if (!folio) {
-                       folio = page_folio(pmd_page(*pmd));
-                       /*
-                        * An anonymous page must be locked, to ensure that a
-                        * concurrent reuse_swap_page() sees stable mapcount;
-                        * but reuse_swap_page() is not used on shmem or file,
-                        * and page lock must not be taken when zap_pmd_range()
-                        * calls __split_huge_pmd() while i_mmap_lock is held.
-                        */
-                       if (folio_test_anon(folio)) {
-                               if (unlikely(!folio_trylock(folio))) {
-                                       folio_get(folio);
-                                       _pmd = *pmd;
-                                       spin_unlock(ptl);
-                                       folio_lock(folio);
-                                       spin_lock(ptl);
-                                       if (unlikely(!pmd_same(*pmd, _pmd))) {
-                                               folio_unlock(folio);
-                                               folio_put(folio);
-                                               folio = NULL;
-                                               goto repeat;
-                                       }
-                                       folio_put(folio);
-                               }
-                               do_unlock_folio = true;
-                       }
-               }
-       } else if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
-               goto out;
-       __split_huge_pmd_locked(vma, pmd, range.start, freeze);
+       if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) ||
+           is_pmd_migration_entry(*pmd))
+               __split_huge_pmd_locked(vma, pmd, range.start, freeze);
+
 out:
        spin_unlock(ptl);
-       if (do_unlock_folio)
-               folio_unlock(folio);
        /*
         * No need to double call mmu_notifier->invalidate_range() callback.
         * They are 3 cases to consider inside __split_huge_pmd_locked():