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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B11FD637A9 for ; Wed, 13 Nov 2024 18:50:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id ECA106B007B; Wed, 13 Nov 2024 13:50:21 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E7A3A6B008C; Wed, 13 Nov 2024 13:50:21 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D41D36B0093; Wed, 13 Nov 2024 13:50:21 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id B6ADE6B007B for ; Wed, 13 Nov 2024 13:50:21 -0500 (EST) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 3BC8A40AAE for ; Wed, 13 Nov 2024 18:50:21 +0000 (UTC) X-FDA: 82781961780.02.91D2A2F Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf06.hostedemail.com (Postfix) with ESMTP id 4584C180005 for ; Wed, 13 Nov 2024 18:49:48 +0000 (UTC) Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=rt8QDIsl; dmarc=none; spf=none (imf06.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1731523756; a=rsa-sha256; cv=none; b=TyAYDzas1HqePd4SscFPwCYt7ipPZMia9RmgNnrBfhqa81gCST0wi0fGcA7QGhL3VJ7wmG ytYl9588TUn6h4BXtzRzChJKiwrSnHBPE3qc0PQ8TUe3OQRjcEZikvFXN0Q7UMpGTixkbE pVREdnjhRIRUIzupgos+oEgB3Fj6PyY= ARC-Authentication-Results: i=1; imf06.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=rt8QDIsl; dmarc=none; spf=none (imf06.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1731523756; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=nq4bIv/oWAf5S/k6VezA2o3s5y3i68pnNRbJOq/1fys=; b=60z1r30JdLiQxtLyJ59hgDKKa2Wf9rNr9Agxl4tTbrcKPRL128drwmh9fHUmB6ocSudofP ZtoCksow3bugQEUPiBurAhCAwYcvs80x9jSFQHahYVM1OcaQMnrTikGNLtdKZIzlB2mOvz JvKE6fRpNfHULpk1CiVeQZ7eEyK1lZ0= 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=nq4bIv/oWAf5S/k6VezA2o3s5y3i68pnNRbJOq/1fys=; b=rt8QDIslv6vKhdttNZX4KMHBgg 5rl21C15AExxBj/UuxibOZ2pLvOH/X3tEz3ttM3USKRU5DH5BxqCMPo2D7155b2C5MVBhca4QsiBr Mgq35ZgaRJHrSu5zftli9ajbT1duhfPDFqr/hvIrY3y+IJM/G7i5VSGDMoD/ZKLApifIHrkVaygi7 sZUkmgn8iqs/c5fd4iZFI7CMAvcAp9QEw3jwAyNqraRoxBtSDdBHkZPCwQmjAICvJFXJyXdtcJD6r mXXkAWh4dch5sGD4hQX9Vg0vPPGISrrf1RrQrh28zscIdV1AVQW7i8Z+o0/cV/rIfyEWvICM880k8 2LDKjB8w==; Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tBIRN-0000000GmSQ-0rjk; Wed, 13 Nov 2024 18:50:09 +0000 Date: Wed, 13 Nov 2024 18:50:08 +0000 From: Matthew Wilcox To: Luis Chamberlain Cc: hch@lst.de, hare@suse.de, david@fromorbit.com, djwong@kernel.org, john.g.garry@oracle.com, ritesh.list@gmail.com, kbusch@kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org, gost.dev@samsung.com, p.raghav@samsung.com, da.gomez@samsung.com, kernel@pankajraghav.com Subject: Re: [RFC 3/8] fs/buffer: restart block_read_full_folio() to avoid array overflow Message-ID: References: <20241113094727.1497722-1-mcgrof@kernel.org> <20241113094727.1497722-4-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241113094727.1497722-4-mcgrof@kernel.org> X-Rspam-User: X-Rspamd-Queue-Id: 4584C180005 X-Rspamd-Server: rspam11 X-Stat-Signature: syu9yaytbxg1nymrz3wcgdd6uhi44cpd X-HE-Tag: 1731523788-789206 X-HE-Meta: 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 mUpvp/np +YWBiO6uL2F+uLVd85rNSBsOC6o4FtHAStfqFGo0SU33A38beXWiywBDFMQZu/KI8tsZM091wBCuQnuUGE/8CaOW7u9ZqFq90JGWOWM8qQLevrRXUjE1nsTVCvCatTTDQhjNewUmtcVJUS3a7eCxkojdFhvxCgSHVpaAJonSRQmoSdMrNd0ZnlZmqvK5p8SmZUAzfNJpWd3/ixFtrC0F4S150EQ/GnsmjAVPHxslV7ktxrkTjDcW06IMDlMZFKxH/K6SDHGurLdey2lxgK472DlGwkA/xt2Pm1GWbTzz9WaGEAv2fmWb8ZH6MUcrMPVU7RZpNIhKNE+pztnUkPAngQmj8N/o5rCjddhe8 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Nov 13, 2024 at 01:47:22AM -0800, Luis Chamberlain wrote: > +++ b/fs/buffer.c > @@ -2366,7 +2366,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > { > struct inode *inode = folio->mapping->host; > sector_t iblock, lblock; > - struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE]; > + struct buffer_head *bh, *head, *restart_bh = NULL, *arr[MAX_BUF_PER_PAGE]; MAX_BUF_PER_PAGE is a pain. There are configs like hexagon which have 256kB pages and so this array ends up being 512 * 8 bytes = 4kB in size which spews stack growth warnings. Can we just make this 8? > @@ -2385,6 +2385,7 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > iblock = div_u64(folio_pos(folio), blocksize); > lblock = div_u64(limit + blocksize - 1, blocksize); > bh = head; > +restart: > nr = 0; > i = 0; > > @@ -2417,7 +2418,12 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > continue; > } > arr[nr++] = bh; > - } while (i++, iblock++, (bh = bh->b_this_page) != head); > + } while (i++, iblock++, (bh = bh->b_this_page) != head && nr < MAX_BUF_PER_PAGE); > + > + if (nr == MAX_BUF_PER_PAGE && bh != head) > + restart_bh = bh; > + else > + restart_bh = NULL; > > if (fully_mapped) > folio_set_mappedtodisk(folio); > @@ -2450,6 +2456,15 @@ int block_read_full_folio(struct folio *folio, get_block_t *get_block) > else > submit_bh(REQ_OP_READ, bh); > } > + > + /* > + * Found more buffers than 'arr' could hold, > + * restart to submit the remaining ones. > + */ > + if (restart_bh) { > + bh = restart_bh; > + goto restart; > + } > return 0; This isn't right. Let's assume we need 16 blocks to fill in this folio and we have 8 entries in 'arr'. nr = 0; i = 0; do { if (buffer_uptodate(bh)) continue; ... arr[nr++] = bh; } while (i++, iblock++, (bh = bh->b_this_page) != head); for (i = 0; i < nr; i++) { bh = arr[i]; submit_bh(REQ_OP_READ, bh); OK, so first time round, we've submitted 8 I/Os. Now we see that restart_bh is not NULL and so we go round again. This time, we happen to find that the last 8 BHs are uptodate. And so we take this path: if (!nr) { /* * All buffers are uptodate or get_block() returned an * error when trying to map them - we can finish the read. */ folio_end_read(folio, !page_error); oops, we forgot about the 8 buffers we already submitted for read.