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[ Upstream commitbed2cc4826] The __filemap_get_folio() function returns error pointers. It never returns NULL. So use IS_ERR() to check it. Fixes:1da86618bd("fs: Convert aops->write_begin to take a folio") Signed-off-by: ZhangPeng <zhangpeng362@huawei.com> Acked-by: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: Richard Weinberger <richard@nod.at> Signed-off-by: Sasha Levin <sashal@kernel.org>