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 C69EFC433EF for ; Wed, 24 Nov 2021 20:05:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=lJ56Q9XEYdwATuviD2k0Zw3GVJYZgO8mZJWCu17Qrjs=; b=V/9ElvpZuEoJm7 sYTCc+l50247Zh9q9ahQShveRMOh7jmFQFY4Cga6U5TUhqcDytONCJQuHqzG6ngMkkeL5FWyxTCcj YNMALpY8DQAAryVVtt5Bd+w5zUG5CPbxzMTE7xntBxxK/OLSIRb+Kh6irAHzeXSbp2Ja4TX0+cBpn 8hKlM/x+XB0+/jNgeGrda8bA9S69jo6drHNi5aY/n71awysoVquxpvRDHVwTvLst44j5/ViOMpipp KWyI+WRFJkJpyaTVtqWLWlCRzNlfuzOiLqCk/qMHlBOTwWwxAJ/YPfFBWCCjiysVA0yUiJN3eENwL jtwetO0sRtpL+q/RcUiA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mpyVB-005kwR-Fa; Wed, 24 Nov 2021 20:04:21 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mpyUz-005kqC-Jt for linux-arm-kernel@bombadil.infradead.org; Wed, 24 Nov 2021 20:04:09 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=OAtizbSoXoPNAyMg215cuoX14RfVf7vO6HnqYrV3Dvk=; b=pxzUkXYfltPbHw3FE40BsyvVC7 q4ztiAKAh9byHa+doug0X32e1mx36FUzfwLCiduYtt8QsQkbTSbkx8rBjcJuIEIoHDU20SEPslrtv aii6BxwmJAhz2jwsFlCGq9xm5OajI8ekPEy4Mqu0PWeXNpXx4DqN2dO+jhaBLFPxibEOqbbPap9kz 8hJIYZoj+Zo4YwJWjUUXqgOiIkexnMHh1II250x7Gy2c6CToeqOJJvXycORVmnogatzbWhQ9v5WVB 5Azf0IIf4TYYwihfL8WBzt1yNge3rFW3tQIm07tHkpz8QXVV3OMm2hQWnGTYXtG6Kw4Kd8+/dnFER KDp5jGhA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1mpyUo-003BgI-Pa; Wed, 24 Nov 2021 20:03:58 +0000 Date: Wed, 24 Nov 2021 20:03:58 +0000 From: Matthew Wilcox To: Catalin Marinas Cc: Linus Torvalds , Josef Bacik , David Sterba , Andreas Gruenbacher , Al Viro , Andrew Morton , Will Deacon , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-btrfs@vger.kernel.org Subject: Re: [PATCH 3/3] btrfs: Avoid live-lock in search_ioctl() on hardware with sub-page faults Message-ID: References: <20211124192024.2408218-1-catalin.marinas@arm.com> <20211124192024.2408218-4-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20211124192024.2408218-4-catalin.marinas@arm.com> 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, Nov 24, 2021 at 07:20:24PM +0000, Catalin Marinas wrote: > +++ b/fs/btrfs/ioctl.c > @@ -2223,7 +2223,8 @@ static noinline int search_ioctl(struct inode *inode, > > while (1) { > ret = -EFAULT; > - if (fault_in_writeable(ubuf + sk_offset, *buf_size - sk_offset)) > + if (fault_in_exact_writeable(ubuf + sk_offset, > + *buf_size - sk_offset)) > break; > > ret = btrfs_search_forward(root, &key, path, sk->min_transid); Couldn't we avoid all of this nastiness by doing ... @@ -2121,10 +2121,9 @@ static noinline int copy_to_sk(struct btrfs_path *path, * problem. Otherwise we'll fault and then copy the buffer in * properly this next time through */ - if (copy_to_user_nofault(ubuf + *sk_offset, &sh, sizeof(sh))) { - ret = 0; + ret = __copy_to_user_nofault(ubuf + *sk_offset, &sh, sizeof(sh)); + if (ret) goto out; - } *sk_offset += sizeof(sh); @@ -2196,6 +2195,7 @@ static noinline int search_ioctl(struct inode *inode, int ret; int num_found = 0; unsigned long sk_offset = 0; + unsigned long next_offset = 0; if (*buf_size < sizeof(struct btrfs_ioctl_search_header)) { *buf_size = sizeof(struct btrfs_ioctl_search_header); @@ -2223,7 +2223,8 @@ static noinline int search_ioctl(struct inode *inode, while (1) { ret = -EFAULT; - if (fault_in_writeable(ubuf + sk_offset, *buf_size - sk_offset)) + if (fault_in_writeable(ubuf + sk_offset + next_offset, + *buf_size - sk_offset - next_offset)) break; ret = btrfs_search_forward(root, &key, path, sk->min_transid); @@ -2235,11 +2236,12 @@ static noinline int search_ioctl(struct inode *inode, ret = copy_to_sk(path, &key, sk, buf_size, ubuf, &sk_offset, &num_found); btrfs_release_path(path); - if (ret) + if (ret > 0) + next_offset = ret; + else if (ret < 0) break; - } - if (ret > 0) + if (ret == -ENOSPC || ret > 0) ret = 0; err: sk->nr_items = num_found; (not shown: the tedious bits where the existing 'ret = 1' are converted to 'ret = -ENOSPC' in copy_to_sk()) (where __copy_to_user_nofault() is a new function that does exactly what copy_to_user_nofault() does, but returns the number of bytes copied) That way, the existing fault_in_writable() will get the fault, and we don't need to probe every 16 bytes. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel