From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0720917A2E2; Mon, 31 Mar 2025 05:38:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743399529; cv=none; b=DoVRUx0y+rrg5Xoj5zMaAQ145GBX2f7Y+QqQhPEDrLSf3KLAbzM7iB9UN0jcTT2UbOYdIbtidlAOTOMxk1JEfFUzXVE2jo5L7zCiEFhOp2oTfgyjkQ8ePzY9t3mjP5ZOlz9K9Qk99SoOEp+kS0QJgiCHjNJ1NTILiqUUL5erO8w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743399529; c=relaxed/simple; bh=O+nGkDYvtL7d3Qqm+1UtASwmM5sd23/5AKPzIlKKH14=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ECm1KpuNKeDENrDdGbLf1mRJvpngYv9n0IPEaF6sG5vdLx7wQQ03LFzEdW0Chm1lKeg25AFDb8MCQUcezQPAyffunh9kLPzijTmth708yWLmqg0jP1+BX5hnJa/+9G4A2t0EGloyu1+rKDnTAi+aT5F/hg0c4a4QwWTNoMSyPO4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=Icr85zrj; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="Icr85zrj" Received: from [10.95.65.22] (unknown [167.220.238.22]) by linux.microsoft.com (Postfix) with ESMTPSA id 3B0282111439; Sun, 30 Mar 2025 22:38:39 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 3B0282111439 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1743399521; bh=Ga+JCIeKoiFxHXkSSUu0P9tSi9JTYZkWrviPT8lbSaI=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Icr85zrj5xsXnf7Gyrpdb9y6S9lOLkFGBRaQtrlBEHyPnyEv2SKPtbOIuTsGXPeSX mC54kMNRj0rNjatFaqG8FkMBqyWJ6Gvt+AASzNMJ0n3KoK2xQdl7SKnOcXzbWieRZC 0KbXu+eUE+7xC5ZYEAC7dtlLbBPlXuw/mDY+rQf4= Message-ID: <32de9597-d609-4e12-8219-ea7205bdc7d8@linux.microsoft.com> Date: Mon, 31 Mar 2025 11:08:35 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/2] uio_hv_generic: Fix sysfs creation path for ring buffer To: Michael Kelley , "K . Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Greg Kroah-Hartman , Stephen Hemminger Cc: "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "stable@kernel.org" , Saurabh Sengar References: <20250328052745.1417-1-namjain@linux.microsoft.com> <20250328052745.1417-2-namjain@linux.microsoft.com> Content-Language: en-US From: Naman Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/30/2025 9:05 PM, Michael Kelley wrote: > From: Naman Jain Sent: Thursday, March 27, 2025 10:28 PM >> >> On regular bootup, devices get registered to VMBus first, so when >> uio_hv_generic driver for a particular device type is probed, >> the device is already initialized and added, so sysfs creation in >> uio_hv_generic probe works fine. However, when device is removed >> and brought back, the channel rescinds and device again gets >> registered to VMBus. However this time, the uio_hv_generic driver is >> already registered to probe for that device and in this case sysfs >> creation is tried before the device's kobject gets initialized >> completely. >> >> Fix this by moving the core logic of sysfs creation for ring buffer, >> from uio_hv_generic to HyperV's VMBus driver, where rest of the sysfs >> attributes for the channels are defined. While doing that, make use >> of attribute groups and macros, instead of creating sysfs directly, >> to ensure better error handling and code flow. >> >> Problem path: >> vmbus_process_offer (new offer comes for the VMBus device) >> vmbus_add_channel_work >> vmbus_device_register >> |-> device_register >> | |... >> | |-> hv_uio_probe >> | |... >> | |-> sysfs_create_bin_file (leads to a warning as >> | primary channel's kobject, which is used to >> | create sysfs is not yet initialized) >> |-> kset_create_and_add >> |-> vmbus_add_channel_kobj (initialization of primary channel's >> kobject happens later) >> >> Above code flow is sequential and the warning is always reproducible in >> this path. >> >> Fixes: 9ab877a6ccf8 ("uio_hv_generic: make ring buffer attribute for primary channel") >> Cc: stable@kernel.org >> Suggested-by: Saurabh Sengar >> Suggested-by: Michael Kelley >> Signed-off-by: Naman Jain >> --- >> drivers/hv/hyperv_vmbus.h | 6 ++ >> drivers/hv/vmbus_drv.c | 110 ++++++++++++++++++++++++++++++++++- >> drivers/uio/uio_hv_generic.c | 33 +++++------ >> include/linux/hyperv.h | 6 ++ >> 4 files changed, 134 insertions(+), 21 deletions(-) >> > > [snip] > >> +/** >> + * hv_create_ring_sysfs() - create "ring" sysfs entry corresponding to ring buffers for a channel. >> + * @channel: Pointer to vmbus_channel structure >> + * @hv_mmap_ring_buffer: function pointer for initializing the function to be called on mmap of >> + * channel's "ring" sysfs node, which is for the ring buffer of that channel. >> + * Function pointer is of below type: >> + * int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel, >> + * struct vm_area_struct *vma)) >> + * This has a pointer to the channel and a pointer to vm_area_struct, >> + * used for mmap, as arguments. >> + * >> + * Sysfs node for ring buffer of a channel is created along with other fields, however its >> + * visibility is disabled by default. Sysfs creation needs to be controlled when the use-case >> + * is running. >> + * For example, HV_NIC device is used either by uio_hv_generic or hv_netvsc at any given point of >> + * time, and "ring" sysfs is needed only when uio_hv_generic is bound to that device. To avoid >> + * exposing the ring buffer by default, this function is reponsible to enable visibility of >> + * ring for userspace to use. >> + * Note: Race conditions can happen with userspace and it is not encouraged to create new >> + * use-cases for this. This was added to maintain backward compatibility, while solving >> + * one of the race conditions in uio_hv_generic while creating sysfs. >> + * >> + * Returns 0 on success or error code on failure. >> + */ >> +int hv_create_ring_sysfs(struct vmbus_channel *channel, >> + int (*hv_mmap_ring_buffer)(struct vmbus_channel *channel, >> + struct vm_area_struct *vma)) >> +{ >> + struct kobject *kobj = &channel->kobj; >> + struct vmbus_channel *primary_channel = channel->primary_channel ? >> + channel->primary_channel : channel; >> + >> + channel->mmap_ring_buffer = hv_mmap_ring_buffer; >> + channel->ring_sysfs_visible = true; >> + >> + /* >> + * Skip updating the sysfs group if the primary channel is not yet initialized and sysfs >> + * group is not yet created. In those cases, the 'ring' will be created later in >> + * vmbus_device_register() -> vmbus_add_channel_kobj(). >> + */ >> + if (!primary_channel->device_obj->channels_kset) >> + return 0; > > This test doesn't accomplish what you want. It tests if the "channels" directory > has been created, but not if the numbered subdirectory for this channel has been > created. sysfs_update_group() operates on the numbered subdirectory and > could still fail because it hasn't been created yet. > > My recommendation is to not try to do a test, and just let sysfs_update_group() > fail in that case (and ignore the error). > > Michael > Thanks Michael. Will remove it. Regards, Naman >> + >> + return sysfs_update_group(kobj, &vmbus_chan_group); >> +} >> +EXPORT_SYMBOL_GPL(hv_create_ring_sysfs);