From nobody Mon Feb 9 09:10:05 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ED3E9EB64DD for ; Thu, 29 Jun 2023 21:24:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232097AbjF2VYA (ORCPT ); Thu, 29 Jun 2023 17:24:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54556 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230308AbjF2VXw (ORCPT ); Thu, 29 Jun 2023 17:23:52 -0400 Received: from smtp-relay-internal-1.canonical.com (smtp-relay-internal-1.canonical.com [185.125.188.123]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D707030EC for ; Thu, 29 Jun 2023 14:23:50 -0700 (PDT) Received: from mail-ot1-f70.google.com (mail-ot1-f70.google.com [209.85.210.70]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by smtp-relay-internal-1.canonical.com (Postfix) with ESMTPS id E66CB3F84D for ; Thu, 29 Jun 2023 21:23:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=canonical.com; s=20210705; t=1688073828; bh=YSYJcPCyfrgfbs0zHyOclQwwCoyKaiH+S5JijMPDsyo=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=fcnAuz2MaQjiocWTKRoSq+lF/Nmba+f1/hS35beJ142ZsioE8twv9afbIaZsqmAx9 ef/CjWXIZ90SYyZh/0KBq2/+JODaDrblQbFtKE2mq6uyhPfYQZbrfzdHB9hCXW4rmm 2HqfmctaRcAtPBhwDjzES3+el6lJyC4svNqsDj4yee8eTappxChCyfOrgRyFc3kJ4E NIqeCzFBWbeokkx0elcwD2hgRzBWTDdvrk5xbDWOoe1Hu9OY/iesgfaHpvDjXn821/ KQmozN2wOhPQyVmr+a9Dfna5eBjLsPA348CJYJ+gE2gz0L/pPLIi5LBRqfV+MpNdbF HjnsMfjAhMVLQ== Received: by mail-ot1-f70.google.com with SMTP id 46e09a7af769-6b8810af3adso1220780a34.1 for ; Thu, 29 Jun 2023 14:23:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688073825; x=1690665825; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=YSYJcPCyfrgfbs0zHyOclQwwCoyKaiH+S5JijMPDsyo=; b=H5CVyksZpm2FOjTzfewIRhVsB/Wn2d09tjQ5Ktf4/8l8eGf87wUMZvYx/d+gLrpDIk 90FE7PsXATSawtmmmcFWuNVIjLHC25G5hMevPmdczSISnbNo8CUVvcPp5Ig2SStSqe7j 6/kBt7af+DeERLiGJpzS2A+nrYZKc2/Nd6yFS3dVkEAcCiSQ69ghq5/tMRTERBrCFCF6 iZyGNL0LwVXTSNZ1DT1XjwLKaf9GrOwHyGaq9v0y85No09h7VzoIvltXBUjRQ8uyub3m 6W4NgtF6xoY8lu3LvdDXaDEdqb7dteboGqjUm8gCUDyRkSXaFo4kmIxHGuRPDuuIk0kT X6Pg== X-Gm-Message-State: AC+VfDyZu/h86wFnqFr2tdzcdvQ0IJyCZZPxE+igG0gggk6Gq6A2pGjk jWpByV7qHTq0naXE5mtps0P2QR58PgEnfdH2G9yrUiCbx6Ha8j/XfRpV72jREIIUVD44R7TrSuU vQtSU//YyTliotqpLfrtwtlUwbbUZSaaJSxIlJmPnSw== X-Received: by 2002:a05:6830:1be9:b0:6b5:be09:5332 with SMTP id k9-20020a0568301be900b006b5be095332mr1084416otb.23.1688073825098; Thu, 29 Jun 2023 14:23:45 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ52tAeUctNAM3SElt+HV9JGomtruQtp/V8Pv84ClN4z/6mDsIK+0IrLE5czLp639HOCoDpqvg== X-Received: by 2002:a05:6830:1be9:b0:6b5:be09:5332 with SMTP id k9-20020a0568301be900b006b5be095332mr1084406otb.23.1688073824802; Thu, 29 Jun 2023 14:23:44 -0700 (PDT) Received: from localhost.localdomain ([2804:14c:4e1:83a2:7720:9030:a195:e622]) by smtp.gmail.com with ESMTPSA id q6-20020a9d6646000000b006b871010cb1sm2711764otm.46.2023.06.29.14.23.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Jun 2023 14:23:44 -0700 (PDT) From: Mauricio Faria de Oliveira To: Jens Axboe , linux-block@vger.kernel.org Cc: "Isaac J. Manjarres" , linux-kernel@vger.kernel.org Subject: [PATCH 2/2] loop: do not enforce max_loop hard limit by (new) default Date: Thu, 29 Jun 2023 18:22:56 -0300 Message-Id: <20230629212256.918239-3-mfo@canonical.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230629212256.918239-1-mfo@canonical.com> References: <20230629212256.918239-1-mfo@canonical.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Problem: The max_loop parameter is used for 2 different purposes: 1) initial number of loop devices to pre-create on init 2) maximum number of loop devices to add on access/open() Historically, its default value (zero) caused 1) to create non-zero number of devices (CONFIG_BLK_DEV_LOOP_MIN_COUNT), and no hard limit on 2) to add devices with autoloading. However, the default value changed in commit 85c50197716c ("loop: Fix the max_loop commandline argument treatment when it is set to 0") to CONFIG_BLK_DEV_LOOP_MIN_COUNT, for max_loop=3D0 not to pre-create devices. That does improve 1), but unfortunately it breaks 2), as the default behavior changed from no-limit to hard-limit. Example: For example, this userspace code broke for N >=3D CONFIG, if the user relied on the default value 0 for max_loop: mknod("/dev/loopN"); open("/dev/loopN"); // now fails with ENXIO Though affected users may "fix" it with (loop.)max_loop=3D0, this means to require a kernel parameter change on stable kernel update (that commit Fixes: an old commit in stable). Solution: The original semantics for the default value in 2) can be applied if the parameter is not set (ie, default behavior). This still keeps the intended function in 1) and 2) if set, and that commit's intended improvement in 1) if max_loop=3D0. Before 85c50197716c: - default: 1) CONFIG devices 2) no limit - max_loop=3D0: 1) CONFIG devices 2) no limit - max_loop=3DX: 1) X devices 2) X limit After 85c50197716c: - default: 1) CONFIG devices 2) CONFIG limit (*) - max_loop=3D0: 1) 0 devices (*) 2) no limit - max_loop=3DX: 1) X devices 2) X limit This commit: - default: 1) CONFIG devices 2) no limit (*) - max_loop=3D0: 1) 0 devices 2) no limit - max_loop=3DX: 1) X devices 2) X limit Future: The issue/regression from that commit only affects code under the CONFIG_BLOCK_LEGACY_AUTOLOAD deprecation guard, thus the fix too is contained under it. Once that deprecated functionality/code is removed, the purpose 2) of max_loop (hard limit) is no longer in use, so the module parameter description can be changed then. Tests: Linux 6.4-rc7 CONFIG_BLK_DEV_LOOP_MIN_COUNT=3D8 CONFIG_BLOCK_LEGACY_AUTOLOAD=3Dy - default (original) # ls -1 /dev/loop* /dev/loop-control /dev/loop0 ... /dev/loop7 # ./test-loop open: /dev/loop8: No such device or address - default (patched) # ls -1 /dev/loop* /dev/loop-control /dev/loop0 ... /dev/loop7 # ./test-loop # - max_loop=3D0 (original & patched): # ls -1 /dev/loop* /dev/loop-control # ./test-loop # - max_loop=3D8 (original & patched): # ls -1 /dev/loop* /dev/loop-control /dev/loop0 ... /dev/loop7 # ./test-loop open: /dev/loop8: No such device or address - max_loop=3D0 (patched; CONFIG_BLOCK_LEGACY_AUTOLOAD is not set) # ls -1 /dev/loop* /dev/loop-control # ./test-loop open: /dev/loop8: No such device or address Fixes: 85c50197716c ("loop: Fix the max_loop commandline argument treatment= when it is set to 0") Signed-off-by: Mauricio Faria de Oliveira --- drivers/block/loop.c | 36 ++++++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 21bcd6ffe241..86060be853bc 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -1777,14 +1777,43 @@ static const struct block_device_operations lo_fops= =3D { /* * If max_loop is specified, create that many devices upfront. * This also becomes a hard limit. If max_loop is not specified, + * the default isn't a hard limit (as before commit 85c50197716c + * changed the default value from 0 for max_loop=3D0 reasons), just * create CONFIG_BLK_DEV_LOOP_MIN_COUNT loop devices at module * init time. Loop devices can be requested on-demand with the * /dev/loop-control interface, or be instantiated by accessing * a 'dead' device node. */ static int max_loop =3D CONFIG_BLK_DEV_LOOP_MIN_COUNT; -module_param(max_loop, int, 0444); + +#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD +static bool max_loop_specified; + +static int max_loop_param_set_int(const char *val, + const struct kernel_param *kp) +{ + int ret; + + ret =3D param_set_int(val, kp); + if (ret < 0) + return ret; + + max_loop_specified =3D true; + return 0; +} + +static const struct kernel_param_ops max_loop_param_ops =3D { + .set =3D max_loop_param_set_int, + .get =3D param_get_int, +}; + +module_param_cb(max_loop, &max_loop_param_ops, &max_loop, 0444); MODULE_PARM_DESC(max_loop, "Maximum number of loop devices"); +#else +module_param(max_loop, int, 0444); +MODULE_PARM_DESC(max_loop, "Initial number of loop devices"); +#endif + module_param(max_part, int, 0444); MODULE_PARM_DESC(max_part, "Maximum number of partitions per loop device"); =20 @@ -2100,7 +2129,7 @@ static void loop_probe(dev_t dev) { int idx =3D MINOR(dev) >> part_shift; =20 - if (max_loop && idx >=3D max_loop) + if (max_loop_specified && max_loop && idx >=3D max_loop) return; loop_add(idx); } @@ -2288,6 +2317,9 @@ module_exit(loop_exit); static int __init max_loop_setup(char *str) { max_loop =3D simple_strtol(str, NULL, 0); +#ifdef CONFIG_BLOCK_LEGACY_AUTOLOAD + max_loop_specified =3D true; +#endif return 1; } =20 --=20 2.39.2