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From:   David Hildenbrand <david@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Rientjes <rientjes@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Yang Shi <shy828301@gmail.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
        Michal Hocko <mhocko@kernel.org>,
        Nadav Amit <namit@vmware.com>, Rik van Riel <riel@surriel.com>,
        Roman Gushchin <guro@fb.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Peter Xu <peterx@redhat.com>,
        Donald Dutile <ddutile@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        Oleg Nesterov <oleg@redhat.com>, Jan Kara <jack@suse.cz>,
        Liang Zhang <zhangliang5@huawei.com>, linux-mm@kvack.org,
        David Hildenbrand <david@redhat.com>
Subject: [PATCH RFC v2 9/9] mm/huge_memory: remove stale locking logic from __split_huge_pmd()
Date:   Wed, 26 Jan 2022 10:55:57 +0100
Message-Id: <20220126095557.32392-10-david@redhat.com>
In-Reply-To: <20220126095557.32392-1-david@redhat.com>
References: <20220126095557.32392-1-david@redhat.com>
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Let's remove the stale logic that was required for reuse_swap_page().

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/huge_memory.c | 32 +-------------------------------
 1 file changed, 1 insertion(+), 31 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 863c933b3b1e..5cc438f92548 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2158,8 +2158,6 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 {
 	spinlock_t *ptl;
 	struct mmu_notifier_range range;
-	bool do_unlock_page = false;
-	pmd_t _pmd;
 
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
 				address & HPAGE_PMD_MASK,
@@ -2178,35 +2176,9 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 			goto out;
 	}
 
-repeat:
 	if (pmd_trans_huge(*pmd)) {
-		if (!page) {
+		if (!page)
 			page = 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 (PageAnon(page)) {
-				if (unlikely(!trylock_page(page))) {
-					get_page(page);
-					_pmd = *pmd;
-					spin_unlock(ptl);
-					lock_page(page);
-					spin_lock(ptl);
-					if (unlikely(!pmd_same(*pmd, _pmd))) {
-						unlock_page(page);
-						put_page(page);
-						page = NULL;
-						goto repeat;
-					}
-					put_page(page);
-				}
-				do_unlock_page = true;
-			}
-		}
 		if (PageMlocked(page))
 			clear_page_mlock(page);
 	} else if (!(pmd_devmap(*pmd) || is_pmd_migration_entry(*pmd)))
@@ -2214,8 +2186,6 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
 	__split_huge_pmd_locked(vma, pmd, range.start, freeze);
 out:
 	spin_unlock(ptl);
-	if (do_unlock_page)
-		unlock_page(page);
 	/*
 	 * No need to double call mmu_notifier->invalidate_range() callback.
 	 * They are 3 cases to consider inside __split_huge_pmd_locked():
-- 
2.34.1