From patchwork Wed Feb 3 13:20:21 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jinpu Wang X-Patchwork-Id: 375960 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 070AAC433DB for ; Wed, 3 Feb 2021 13:21:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E3A864F55 for ; Wed, 3 Feb 2021 13:21:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229979AbhBCNVw (ORCPT ); Wed, 3 Feb 2021 08:21:52 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230248AbhBCNVr (ORCPT ); Wed, 3 Feb 2021 08:21:47 -0500 Received: from mail-wr1-x436.google.com (mail-wr1-x436.google.com [IPv6:2a00:1450:4864:20::436]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BDF45C06178C for ; Wed, 3 Feb 2021 05:20:31 -0800 (PST) Received: by mail-wr1-x436.google.com with SMTP id q7so24229029wre.13 for ; Wed, 03 Feb 2021 05:20:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloud.ionos.com; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=/Q85vcvTRwqOQln7ONod8UaPXYEVKrd8O7nB76luOHM=; b=VSq/Tq18U/g3RagnsHbxoGrjQ8RXYNWfZd088OHvmvNTjj0C1OQzv2cg/hVjaMZhgI kzmPE3oYHs4sCpo8uXlqnO/+jtSFWZH7NVXZ7TaKuZa07s64d5dQ1akwp/eWK/RvVADk VVMuO+Ck8G9o0CjYv4hTsBvIQoxhVXI92NajpyqmPSlKg4cCyY/pOqXSIYLFxve1S5to +0vHk5YTf2YML+u+pFYYIeQGTW53bi4HD1cJRzYD3JoAH2Hj5Pb3OoJznSSjab1w7KNZ 1NZN2ilKxixJieb0ohM3Er5vy7HtD0MmnuHVrdDBHFz2xNZwEVOSNRJdsgQWv0b42xi4 YHlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=/Q85vcvTRwqOQln7ONod8UaPXYEVKrd8O7nB76luOHM=; b=dRisQ7+EaX1TTs/u2J7frl4029eMS7FlHWZ09BRhc25eEI6uN/U1lHtGaUCiTIYAnb vyZlu57inb46H34oPl6jRaYF4vJfdzqgkU5PP1w/eN0GH+ZAsrrDL9RH5/yk2vaNquaP wS2ghx96BhIARaj7gyt28iTSftZYe6n6NlngojvYbypEFtuhepPr5SV7x95R0yuAAPno PPXmjhIbRC/PbajiaEQc1A5izW1jRFnm6v6kA6l3XJUtkmm5wVdNCtzLPvHanyZ07hc6 KBewUosmSjWtgshtEsevSgu2goTBq/FSCIAPaKVbPjQxBRN9j8zcb+xdP3Dh0FPc7tjV Gkfg== X-Gm-Message-State: AOAM532LMg/PpVY8HFr7MH23YZJ4fCjByY5HAokaotT34c/b6NrwTNEA xxz6W1vffp2e/EW25NK+vQOgQqMe7DpapA== X-Google-Smtp-Source: ABdhPJzalN3t5nMp4frtKnib2fiQWkX/JacxAxKNJO/UWKT+gUZWvw+by6KGDUFpR8xfpLgP7XEJeA== X-Received: by 2002:a5d:4046:: with SMTP id w6mr3425430wrp.369.1612358430535; Wed, 03 Feb 2021 05:20:30 -0800 (PST) Received: from jwang-Latitude-5491.fritz.box ([2001:16b8:4947:3c00:7cf4:7472:391:9d0d]) by smtp.gmail.com with ESMTPSA id d10sm3738430wrn.88.2021.02.03.05.20.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Feb 2021 05:20:30 -0800 (PST) From: Jack Wang To: gregkh@linuxfoundation.org, sashal@kernel.org, stable@vger.kernel.org Cc: Ming Lei , Christoph Hellwig , Hannes Reinecke , Mike Snitzer , Bart Van Assche , Jens Axboe Subject: [stable-4.19 7/8] block: don't release queue's sysfs lock during switching elevator Date: Wed, 3 Feb 2021 14:20:21 +0100 Message-Id: <20210203132022.92406-8-jinpu.wang@cloud.ionos.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210203132022.92406-1-jinpu.wang@cloud.ionos.com> References: <20210203132022.92406-1-jinpu.wang@cloud.ionos.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ming Lei cecf5d87ff20 ("block: split .sysfs_lock into two locks") starts to release & acquire sysfs_lock before registering/un-registering elevator queue during switching elevator for avoiding potential deadlock from showing & storing 'queue/iosched' attributes and removing elevator's kobject. Turns out there isn't such deadlock because 'q->sysfs_lock' isn't required in .show & .store of queue/iosched's attributes, and just elevator's sysfs lock is acquired in elv_iosched_store() and elv_iosched_show(). So it is safe to hold queue's sysfs lock when registering/un-registering elevator queue. The biggest issue is that commit cecf5d87ff20 assumes that concurrent write on 'queue/scheduler' can't happen. However, this assumption isn't true, because kernfs_fop_write() only guarantees that concurrent write aren't called on the same open file, but the write could be from different open on the file. So we can't release & re-acquire queue's sysfs lock during switching elevator, otherwise use-after-free on elevator could be triggered. Fixes the issue by not releasing queue's sysfs lock during switching elevator. Fixes: cecf5d87ff20 ("block: split .sysfs_lock into two locks") Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Greg KH Cc: Mike Snitzer Reviewed-by: Bart Van Assche Signed-off-by: Ming Lei Signed-off-by: Jens Axboe (jwang:cherry picked from commit b89f625e28d44552083f43752f62d8621ded0a04 adjust ctx for 4.19) Signed-off-by: Jack Wang --- block/blk-sysfs.c | 3 ++- block/elevator.c | 31 +------------------------------ 2 files changed, 3 insertions(+), 31 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 899987152701..07494deb1a26 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -933,6 +933,7 @@ int blk_register_queue(struct gendisk *disk) blk_mq_debugfs_register(q); } + mutex_lock(&q->sysfs_lock); /* * The flag of QUEUE_FLAG_REGISTERED isn't set yet, so elevator * switch won't happen at all. @@ -940,6 +941,7 @@ int blk_register_queue(struct gendisk *disk) if (q->request_fn || (q->mq_ops && q->elevator)) { ret = elv_register_queue(q, false); if (ret) { + mutex_unlock(&q->sysfs_lock); mutex_unlock(&q->sysfs_dir_lock); kobject_del(&q->kobj); blk_trace_remove_sysfs(dev); @@ -949,7 +951,6 @@ int blk_register_queue(struct gendisk *disk) has_elevator = true; } - mutex_lock(&q->sysfs_lock); blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q); wbt_enable_default(q); blk_throtl_register_queue(q); diff --git a/block/elevator.c b/block/elevator.c index 2ff0859e8b35..5b51bc5fad9f 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -856,11 +856,9 @@ int elv_register_queue(struct request_queue *q, bool uevent) if (uevent) kobject_uevent(&e->kobj, KOBJ_ADD); - mutex_lock(&q->sysfs_lock); e->registered = 1; if (!e->uses_mq && e->type->ops.sq.elevator_registered_fn) e->type->ops.sq.elevator_registered_fn(q); - mutex_unlock(&q->sysfs_lock); } return error; } @@ -878,11 +876,9 @@ void elv_unregister_queue(struct request_queue *q) kobject_uevent(&e->kobj, KOBJ_REMOVE); kobject_del(&e->kobj); - mutex_lock(&q->sysfs_lock); e->registered = 0; /* Re-enable throttling in case elevator disabled it */ wbt_enable_default(q); - mutex_unlock(&q->sysfs_lock); } } @@ -953,32 +949,11 @@ int elevator_switch_mq(struct request_queue *q, lockdep_assert_held(&q->sysfs_lock); if (q->elevator) { - if (q->elevator->registered) { - mutex_unlock(&q->sysfs_lock); - - /* - * Concurrent elevator switch can't happen becasue - * sysfs write is always exclusively on same file. - * - * Also the elevator queue won't be freed after - * sysfs_lock is released becasue kobject_del() in - * blk_unregister_queue() waits for completion of - * .store & .show on its attributes. - */ + if (q->elevator->registered) elv_unregister_queue(q); - mutex_lock(&q->sysfs_lock); - } ioc_clear_queue(q); elevator_exit(q, q->elevator); - - /* - * sysfs_lock may be dropped, so re-check if queue is - * unregistered. If yes, don't switch to new elevator - * any more - */ - if (!blk_queue_registered(q)) - return 0; } ret = blk_mq_init_sched(q, new_e); @@ -986,11 +961,7 @@ int elevator_switch_mq(struct request_queue *q, goto out; if (new_e) { - mutex_unlock(&q->sysfs_lock); - ret = elv_register_queue(q, true); - - mutex_lock(&q->sysfs_lock); if (ret) { elevator_exit(q, q->elevator); goto out;