From patchwork Mon Jul 22 17:30:48 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Guenter Roeck X-Patchwork-Id: 11053193 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 66802912 for ; Mon, 22 Jul 2019 17:30:53 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 51A03223A6 for ; Mon, 22 Jul 2019 17:30:53 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4411228066; Mon, 22 Jul 2019 17:30:53 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.7 required=2.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D498A26E82 for ; Mon, 22 Jul 2019 17:30:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726347AbfGVRaw (ORCPT ); Mon, 22 Jul 2019 13:30:52 -0400 Received: from mail-pg1-f195.google.com ([209.85.215.195]:46733 "EHLO mail-pg1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726283AbfGVRaw (ORCPT ); Mon, 22 Jul 2019 13:30:52 -0400 Received: by mail-pg1-f195.google.com with SMTP id i8so17969022pgm.13; Mon, 22 Jul 2019 10:30:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:from:to:cc:subject:date:message-id; bh=3WkrBlhQGLRNnJo/MXZZ7vnmbCcs74q4XJirvLk0V8M=; b=sMnH79elSRWNVhT7udK5QBveox3svU97zhfgWSuiCqRHFr423/n22/TjxOGShUPHJ5 glbE8Wkj/A91exHCpMAiiYFTrwYE2AYlLInM/cMkICuEY06qwxfkjqDZbyNJBstapcx5 jKcRXT60w04z9Fuv0T7Bl0HZFY83C7lrE63T4HC9+vEZpE/7LWqKKAYCwhmr6rJN+SUw XYRSydbnF0NZE1keAvOjfQZLePK/QKpKaaLs3BLj750WLkx5I+SCHdGWB4dRiF2KsziF 242EFmmgJr+o1jBWMLck5PWTILTWnu3nKdEzqlxRK01QVEQjJTWjocpHmG4mHeaufh/z OzDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:from:to:cc:subject:date:message-id; bh=3WkrBlhQGLRNnJo/MXZZ7vnmbCcs74q4XJirvLk0V8M=; b=azr9CHQ59Ig9F7Pwh67GYzOFuTlgaehW/DVteIICL3dDq28jIXEbH7x2Sr6JW7xh83 YRyGesMjfYC5jOmQ9BUySq6xj9gWOiDklB/eCYQwVsm4UOGhyW7ih/zhIRCwN+Xphq9J gFx2Bni/UicE69xhdrgLLIQDvwG9qqAKCRr7u68qn4bsCOj8GnTvOKqNYwGNdDqsAVmn miBr6V539URHCFSZuXPbgMP5RoE5ton7h4i2EpyLZWZhPqrNhi9IYb10Y5Lr6vEC6nqu WACSMsZLlxApxwYro4dYPgqyKNTK5R+WwRLywWR2SCnAjgj3qo9ZxxAj3glnF7hoDk7R mITA== X-Gm-Message-State: APjAAAVDjllKVoMA47IEoSxv/h8s/+VS+N+UpCelRLShFOB7MdoQj1nH GwXkZyfHv9RBVGLZgXft6qBMjCzJ X-Google-Smtp-Source: APXvYqybia81FEHbBtIsKy2f17+dgZLRK5oM7wUDCFjbIJnf2XyxwwRcQFfFwNNfePBYPs7mNxd6QQ== X-Received: by 2002:aa7:8d98:: with SMTP id i24mr1343890pfr.199.1563816651231; Mon, 22 Jul 2019 10:30:51 -0700 (PDT) Received: from localhost ([2600:1700:e321:62f0:329c:23ff:fee3:9d7c]) by smtp.gmail.com with ESMTPSA id o12sm30748558pjr.22.2019.07.22.10.30.49 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 22 Jul 2019 10:30:50 -0700 (PDT) From: Guenter Roeck To: Paolo Valente , Jens Axboe Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Guenter Roeck , Hsin-Yi Wang , Nicolas Boichat , Doug Anderson Subject: [PATCH] bfq: Check if bfqq is NULL in bfq_insert_request Date: Mon, 22 Jul 2019 10:30:48 -0700 Message-Id: <1563816648-12057-1-git-send-email-linux@roeck-us.net> X-Mailer: git-send-email 2.7.4 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP In bfq_insert_request(), bfqq is initialized with: bfqq = bfq_init_rq(rq); In bfq_init_rq(), we find: if (unlikely(!rq->elv.icq)) return NULL; Indeed, rq->elv.icq can be NULL if the memory allocation in create_task_io_context() failed. A comment in bfq_insert_request() suggests that bfqq is supposed to be non-NULL if 'at_head || blk_rq_is_passthrough(rq)' is false. Yet, as debugging and practical experience shows, this is not the case in the above situation. This results in the following crash. Unable to handle kernel NULL pointer dereference at virtual address 00000000000001b0 ... Call trace: bfq_setup_cooperator+0x44/0x134 bfq_insert_requests+0x10c/0x630 blk_mq_sched_insert_requests+0x60/0xb4 blk_mq_flush_plug_list+0x290/0x2d4 blk_flush_plug_list+0xe0/0x230 blk_finish_plug+0x30/0x40 generic_writepages+0x60/0x94 blkdev_writepages+0x24/0x30 do_writepages+0x74/0xac __filemap_fdatawrite_range+0x94/0xc8 file_write_and_wait_range+0x44/0xa0 blkdev_fsync+0x38/0x68 vfs_fsync_range+0x68/0x80 do_fsync+0x44/0x80 The problem is relatively easy to reproduce by running an image with failslab enabled, such as with: cd /sys/kernel/debug/failslab echo 10 > probability echo 300 > times Avoid the problem by checking if bfqq is NULL before using it. With the NULL check in place, requests with missing io context are queued immediately, and the crash is no longer seen. Fixes: 18e5a57d79878 ("block, bfq: postpone rq preparation to insert or merge") Reported-by: Hsin-Yi Wang Cc: Hsin-Yi Wang Cc: Nicolas Boichat Cc: Doug Anderson Signed-off-by: Guenter Roeck --- block/bfq-iosched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index 72860325245a..56f3f4227010 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -5417,7 +5417,7 @@ static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq, spin_lock_irq(&bfqd->lock); bfqq = bfq_init_rq(rq); - if (at_head || blk_rq_is_passthrough(rq)) { + if (!bfqq || at_head || blk_rq_is_passthrough(rq)) { if (at_head) list_add(&rq->queuelist, &bfqd->dispatch); else