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    Subject[PATCH 4.4 098/159] memfd: Use radix_tree_deref_slot_protected to avoid the warning.
    Date
    From: zhong jiang <zhongjiang@huawei.com>

    The commit eb4058d8daf8 ("memfd: Fix locking when tagging pins")
    introduces the following warning messages.

    *WARNING: suspicious RCU usage in memfd_wait_for_pins*

    It is because we still use radix_tree_deref_slot without read_rcu_lock.
    We should use radix_tree_deref_slot_protected instead in the case.

    Cc: stable@vger.kernel.org
    Fixes: eb4058d8daf8 ("memfd: Fix locking when tagging pins")
    Signed-off-by: zhong jiang <zhongjiang@huawei.com>
    Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    mm/shmem.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/mm/shmem.c
    +++ b/mm/shmem.c
    @@ -1862,7 +1862,7 @@ static void shmem_tag_pins(struct addres
    spin_lock_irq(&mapping->tree_lock);
    restart:
    radix_tree_for_each_slot(slot, &mapping->page_tree, &iter, start) {
    - page = radix_tree_deref_slot(slot);
    + page = radix_tree_deref_slot_protected(slot, &mapping->tree_lock);
    if (!page || radix_tree_exception(page)) {
    if (radix_tree_deref_retry(page))
    goto restart;

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