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    Subject[PATCH 5.15 876/917] mm/filemap.c: remove bogus VM_BUG_ON
    Date
    From: Matthew Wilcox (Oracle) <willy@infradead.org>

    commit d417b49fff3e2f21043c834841e8623a6098741d upstream.

    It is not safe to check page->index without holding the page lock. It
    can be changed if the page is moved between the swap cache and the page
    cache for a shmem file, for example. There is a VM_BUG_ON below which
    checks page->index is correct after taking the page lock.

    Link: https://lkml.kernel.org/r/20210818144932.940640-1-willy@infradead.org
    Fixes: 5c211ba29deb ("mm: add and use find_lock_entries")
    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Reported-by: <syzbot+c87be4f669d920c76330@syzkaller.appspotmail.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/filemap.c | 1 -
    1 file changed, 1 deletion(-)

    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -2093,7 +2093,6 @@ unsigned find_lock_entries(struct addres
    if (!xa_is_value(page)) {
    if (page->index < start)
    goto put;
    - VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
    if (page->index + thp_nr_pages(page) - 1 > end)
    goto put;
    if (!trylock_page(page))

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