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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable 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 3C70EC54F70 for ; Sun, 19 Apr 2020 23:17:51 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 06C192075E for ; Sun, 19 Apr 2020 23:17:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 06C192075E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=acm.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 685558E0005; Sun, 19 Apr 2020 19:17:50 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 60DE68E0003; Sun, 19 Apr 2020 19:17:50 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4D62C8E0005; Sun, 19 Apr 2020 19:17:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0136.hostedemail.com [216.40.44.136]) by kanga.kvack.org (Postfix) with ESMTP id 330CB8E0003 for ; Sun, 19 Apr 2020 19:17:50 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E798552C1 for ; Sun, 19 Apr 2020 23:17:49 +0000 (UTC) X-FDA: 76726169058.04.milk20_273fad3a6f521 X-HE-Tag: milk20_273fad3a6f521 X-Filterd-Recvd-Size: 5371 Received: from mail-pl1-f195.google.com (mail-pl1-f195.google.com [209.85.214.195]) by imf37.hostedemail.com (Postfix) with ESMTP for ; Sun, 19 Apr 2020 23:17:49 +0000 (UTC) Received: by mail-pl1-f195.google.com with SMTP id y22so3252112pll.4 for ; Sun, 19 Apr 2020 16:17:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=y10OAFrPiAt4TKEL/D56H00tjioHU0owftouG0pGmVs=; b=AkuDv+ZRr3QThzW989GEKoXoZmq0WBWhcLoGUv+54cVa0vguspcsSBkWWilonfJJs1 uMUTRuuRARi+qy7B0iwjkkO5NxcXS7Jp1DkQ3eVKHrFcM7qIkgRITo3tTIdjzg8vWGVu v0HZ3KQDaHpBMB/1Yth/rRgUiUhN9F8k4HuqEu/LP0Q5PzARzygck8fgDkBq+4dVUidC OmvatmPehtmJB9uVvhqDQIR4wRr911wMOEQdN1VEFBkGT42Wmy6o7ApG14mMso1aU8bd qBfGjbuVOVuQ9vb1OXlG9I1B0hlSjZAmMOvkXtLdi6iK3S0MhyAFTQMCLIS3iKdxnXef fqDw== X-Gm-Message-State: AGi0PuZBxJijjEDpKF/HOcBanOoq0HT08PiXDnhzdYpWvy+EwhlKzUHw FqCjDy2F//9AeFfgdzPCk/E= X-Google-Smtp-Source: APiQypKhsvrI8PM8T712YWcOsxumEfkDrBj0hZKU+VjzawT2rtbTHzwbaDbzGHptgsHKL/fIupYMFw== X-Received: by 2002:a17:90a:65c5:: with SMTP id i5mr18067496pjs.18.1587338268810; Sun, 19 Apr 2020 16:17:48 -0700 (PDT) Received: from [100.124.11.78] ([104.129.198.66]) by smtp.gmail.com with ESMTPSA id x4sm25368167pfi.202.2020.04.19.16.17.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 19 Apr 2020 16:17:48 -0700 (PDT) Subject: Re: [PATCH v2 08/10] blktrace: add checks for created debugfs files on setup To: Luis Chamberlain Cc: axboe@kernel.dk, viro@zeniv.linux.org.uk, 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 References: <20200419194529.4872-1-mcgrof@kernel.org> <20200419194529.4872-9-mcgrof@kernel.org> <38240225-e48e-3035-0baa-4929948b23a3@acm.org> <20200419230537.GG11244@42.do-not-panic.com> From: Bart Van Assche Message-ID: Date: Sun, 19 Apr 2020 16:17:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200419230537.GG11244@42.do-not-panic.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit 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 4/19/20 4:05 PM, Luis Chamberlain wrote: > On Sun, Apr 19, 2020 at 03:57:58PM -0700, Bart Van Assche wrote: >> On 4/19/20 12:45 PM, Luis Chamberlain wrote: >>> Even though debugfs can be disabled, enabling BLK_DEV_IO_TRACE will >>> select DEBUG_FS, and blktrace exposes an API which userspace uses >>> relying on certain files created in debugfs. If files are not created >>> blktrace will not work correctly, so we do want to ensure that a >>> blktrace setup creates these files properly, and otherwise inform >>> userspace. >>> >>> Signed-off-by: Luis Chamberlain >>> --- >>> kernel/trace/blktrace.c | 8 +++++--- >>> 1 file changed, 5 insertions(+), 3 deletions(-) >>> >>> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c >>> index 9cc0153849c3..fc32a8665ce8 100644 >>> --- a/kernel/trace/blktrace.c >>> +++ b/kernel/trace/blktrace.c >>> @@ -552,17 +552,19 @@ static int blk_trace_create_debugfs_files(struct blk_user_trace_setup *buts, >>> struct dentry *dir, >>> struct blk_trace *bt) >>> { >>> - int ret = -EIO; >>> - >>> bt->dropped_file = debugfs_create_file("dropped", 0444, dir, bt, >>> &blk_dropped_fops); >>> + if (!bt->dropped_file) >>> + return -ENOMEM; >>> bt->msg_file = debugfs_create_file("msg", 0222, dir, bt, &blk_msg_fops); >>> + if (!bt->msg_file) >>> + return -ENOMEM; >>> bt->rchan = relay_open("trace", dir, buts->buf_size, >>> buts->buf_nr, &blk_relay_callbacks, bt); >>> if (!bt->rchan) >>> - return ret; >>> + return -EIO; >>> return 0; >>> } >> >> I should have had a look at this patch before I replied to the previous >> patch. >> >> Do you agree that the following code can be triggered by >> debugfs_create_file() and also that debugfs_create_file() never returns >> NULL? > > If debugfs is enabled, and not that we know it is in this blktrace code, > as we select it, it can return ERR_PTR(-ERROR) if an error occurs. This is what I found in include/linux/debugfs.h in case debugfs is disabled: static inline struct dentry *debugfs_create_file(const char *name, umode_t mode, struct dentry *parent, void *data, const struct file_operations *fops) { return ERR_PTR(-ENODEV); } I have not found any code path that can cause debugfs_create_file() to return NULL. Did I perhaps overlook something? If not, it's not clear to me why the above patch adds checks that check whether debugfs_create_file() returns NULL? Thanks, Bart.