linux-kernel - [PATCH v3 10/16] mm/huge_memory: remove outdated VM_WARN_ON_ONCE_PAGE from unmap

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Date:   Tue, 29 Mar 2022 18:04:34 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Yang Shi <shy828301@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Donald Dutile <ddutile@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
        Liang Zhang <zhangliang5@...wei.com>,
        Pedro Gomes <pedrodemargomes@...il.com>,
        Oded Gabbay <oded.gabbay@...il.com>, linux-mm@...ck.org,
        David Hildenbrand <david@...hat.com>
Subject: [PATCH v3 10/16] mm/huge_memory: remove outdated VM_WARN_ON_ONCE_PAGE from unmap_page()

We can already theoretically fail to unmap (still having page_mapped()) in
case arch_unmap_one() fails, which can happen on sparc. Failures to
unmap are handled gracefully, just as if there are other references on
the target page: freezing the refcount in split_huge_page_to_list()
will fail if still mapped and we'll simply remap.

In commit 504e070dc08f ("mm: thp: replace DEBUG_VM BUG with VM_WARN when
unmap fails for split") we already converted to VM_WARN_ON_ONCE_PAGE,
let's get rid of it completely now.

This is a preparation for making try_to_migrate() fail on anonymous pages
with GUP pins, which will make this VM_WARN_ON_ONCE_PAGE trigger more
frequently.

Reported-by: Yang Shi <shy828301@...il.com>
Reviewed-by: Yang Shi <shy828301@...il.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/huge_memory.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index dd16819c5edc..70298431e128 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2241,8 +2241,6 @@ static void unmap_page(struct page *page)
 		try_to_migrate(folio, ttu_flags);
 	else
 		try_to_unmap(folio, ttu_flags | TTU_IGNORE_MLOCK);
-
-	VM_WARN_ON_ONCE_PAGE(page_mapped(page), page);
 }
 
 static void remap_page(struct folio *folio, unsigned long nr)
-- 
2.35.1