From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5EF50D1118F for ; Wed, 26 Nov 2025 18:10:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=DXnZBmMMcBqaL+DvhiYDDvgc0bvBDpQl+0qRcxV/rMI=; b=EqJQSOvjIhbsMHkVGN0XbXAIdj P4ZTUm5/JXyQLXZOLfIQlzf/MToo7Vpyhq+iTgBJCesLZQsG8pq8DcMNaoC5sdFWi49h1B5ysVuH0 djCUCYoZtCtZF0OI7C4/sgDzqEQPEu28joST6nhYkCD5d7A4p8x7eKNzQvQOuCojiutvC1gQBz5Du offmFNxh4K9lWNiTn+kZTSBs/Iz7CIXC69+RbbQmUjKi41WWb+VCAdN1JnreeXJQHjXxJ9HaRoek9 7AXjUYV8lNDSdpPXThqP+o0ptHNXMqdUni39wtpY7jrKWNjogcJeVZmUoqb2JSbd9UY3gfczUdnJK DpFC1WUw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vOJyV-0000000FTvt-1KFU; Wed, 26 Nov 2025 18:10:45 +0000 Received: from zeniv.linux.org.uk ([2a03:a000:7:0:5054:ff:fe1c:15ff]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vOJyR-0000000FTvL-3Kbd for linux-arm-kernel@lists.infradead.org; Wed, 26 Nov 2025 18:10:41 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=linux.org.uk; s=zeniv-20220401; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=DXnZBmMMcBqaL+DvhiYDDvgc0bvBDpQl+0qRcxV/rMI=; b=UwduLDd2QSBZYnTFsQNeZ7gUhb ugR7BEq1Awwb0Sl1pJANgCHa9RbW5fJogb979YgNPHGV9moAmTbrJ6s+dLcDAnnFOkdE4tVuubBSH 1VmQFY5MTGbuZQOjMR/K5XUeGRnPdTc96EEZU292HRpDwwwP/7Qp6fj3DKKvaETaf3TfjYtpFLcZh 2WxqQkz0AeUZ06OWl+kipIg5QxxFnOtma8Aeti10N6RW81xfDSQB5RODA2zZdiOKlBpbAYz0kgd0d w5QRtNcGq0hOCNpK0/DWciUgfLnpEdCNlBBC2JezPucP0NYoOXK57GRna2MFXOhCuGmbsTWXDf04q 5dglf4Yw==; Received: from viro by zeniv.linux.org.uk with local (Exim 4.99 #2 (Red Hat Linux)) id 1vOJyJ-0000000Gm9v-1MMj; Wed, 26 Nov 2025 18:10:31 +0000 Date: Wed, 26 Nov 2025 18:10:31 +0000 From: Al Viro To: Xie Yuanbin Cc: brauner@kernel.org, jack@suse.cz, linux@armlinux.org.uk, will@kernel.org, nico@fluxnic.net, akpm@linux-foundation.org, hch@lst.de, jack@suse.com, wozizhi@huaweicloud.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, lilinjie8@huawei.com, liaohua4@huawei.com, wangkefeng.wang@huawei.com, pangliyuan1@huawei.com Subject: Re: [RFC PATCH] vfs: Fix might sleep in load_unaligned_zeropad() with rcu read lock held Message-ID: <20251126181031.GA3538@ZenIV> References: <20251126090505.3057219-1-wozizhi@huaweicloud.com> <20251126101952.174467-1-xieyuanbin1@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251126101952.174467-1-xieyuanbin1@huawei.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251126_101040_102153_492EE5A6 X-CRM114-Status: GOOD ( 10.62 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 26, 2025 at 06:19:52PM +0800, Xie Yuanbin wrote: > When the path is initialized with LOOKUP_RCU flag in path_init(), the > rcu read lock will be acquired. Inside the rcu critical section, > load_unaligned_zeropad() may be called. According to the comments of > load_unaligned_zeropad(), when loading the memory, a page fault may be > triggered in the very unlikely case. > Add pagefault_disable() to handle this situation. Way too costly, IMO. That needs to be dealt with in page fault handler and IIRC arm used to do that; did that get broken at some point?