From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from zeniv.linux.org.uk (zeniv.linux.org.uk [62.89.141.173]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F02D279DAB; Wed, 26 Nov 2025 18:10:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=62.89.141.173 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764180639; cv=none; b=KkYzY7RrRJwUfFoL1Jl92NIA/T3nbwaVk71beHI2cq66KeNMzSxgEPRN5ozCDI6QkHCKuCQu/lTQHYT/B7ukpnhIUvC2dJwr8GNHCAmE3lb+BPduI/12z8ao5C+YWxXSWROumP03K2gHzCPZ+qR+PgNxbrZUR340a1J2ovaEOtI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764180639; c=relaxed/simple; bh=13OJotMS9uxD2wgIVDkGSwJx750XMvizYmyzY4oLYb8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=EPo84TFuRvvVT4x9U0lI5k9UYYgEkHsxwVriwy6gBim4lb1APFkQuqqJPCyokK0V3qQuEHMaLStsNbCdzL+QVviiNfbt30j4Q4M+sMk3EYOzGJVEu0y6JNHuA3VdjSPCWvZisV3Aqxvrj2OIg3Ax6xOelZU1+QLjphOaVR4i0Vc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk; spf=none smtp.mailfrom=ftp.linux.org.uk; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b=UwduLDd2; arc=none smtp.client-ip=62.89.141.173 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=ftp.linux.org.uk Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linux.org.uk header.i=@linux.org.uk header.b="UwduLDd2" 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> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251126101952.174467-1-xieyuanbin1@huawei.com> Sender: Al Viro 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?