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 X-Spam-Level: X-Spam-Status: No, score=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 50C74C2BA19 for ; Tue, 14 Apr 2020 15:41:02 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 04519206D5 for ; Tue, 14 Apr 2020 15:41:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Hzraabfb" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 04519206D5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 945428E0027; Tue, 14 Apr 2020 11:41:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8F4B78E0007; Tue, 14 Apr 2020 11:41:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8317F8E0027; Tue, 14 Apr 2020 11:41:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0230.hostedemail.com [216.40.44.230]) by kanga.kvack.org (Postfix) with ESMTP id 68E8C8E0007 for ; Tue, 14 Apr 2020 11:41:01 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 27031181AEF23 for ; Tue, 14 Apr 2020 15:41:01 +0000 (UTC) X-FDA: 76706873922.02.beast82_7d440ec05c257 X-HE-Tag: beast82_7d440ec05c257 X-Filterd-Recvd-Size: 2771 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Tue, 14 Apr 2020 15:41:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=uWqF91n+VhADIdhuzisMtYavXGhMw/jiYsc8UWNs3HE=; b=HzraabfbjAbD5+L7alBwAuxQg4 rZ9TPhmym2Y8LbdBNXVWQtDEQyqbmeqD25/XbZE3tUhzhH/JcUGRIhNkCbpWtxjVXIz/rlIO6KHuX aZYI6KMDyzAHtTU8UC2ruyG2iigFrhPaPbyHnOP8pUCpiDIOELu57X5myWxab1z9jknAG44shMPQW 7is7vPB71BKCuvvh5xQkSMafc65QzJnst7pERFZ/HSXWvbWmkAGDwhYTbQoFW/UzVHYsb5TXAGm9g ewvBfmh/GN5FW+TwYsmj2pj1t2jE0yuap2tRGO56LY1erH+/++9Q9aZoERVLOVs/ssgCjrbF5QeVW FZIPSzdw==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jONg4-00008t-OZ; Tue, 14 Apr 2020 15:40:44 +0000 Date: Tue, 14 Apr 2020 08:40:44 -0700 From: Christoph Hellwig To: Luis Chamberlain Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk, bvanassche@acm.org, gregkh@linuxfoundation.org, rostedt@goodmis.org, mingo@redhat.com, jack@suse.cz, ming.lei@redhat.com, nstange@suse.de, akpm@linux-foundation.org, mhocko@suse.com, yukuai3@huawei.com, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Omar Sandoval , Hannes Reinecke , Michal Hocko Subject: Re: [PATCH 3/5] blktrace: refcount the request_queue during ioctl Message-ID: <20200414154044.GB25765@infradead.org> References: <20200414041902.16769-1-mcgrof@kernel.org> <20200414041902.16769-4-mcgrof@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200414041902.16769-4-mcgrof@kernel.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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: On Tue, Apr 14, 2020 at 04:19:00AM +0000, Luis Chamberlain wrote: > Ensure that the request_queue is refcounted during its full > ioctl cycle. This avoids possible races against removal, given > blk_get_queue() also checks to ensure the queue is not dying. > > This small race is possible if you defer removal of the request_queue > and userspace fires off an ioctl for the device in the meantime. Hmm, where exactly does the race come in so that it can only happen after where you take the reference, but not before it? I'm probably missing something, but that just means it needs to be explained a little better :)