From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B2FAD3FF890; Wed, 8 Jul 2026 08:14:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783498446; cv=none; b=i5StryYDD2NZhY0BtzyWhoy156ck9oD45xVxm+T8hY8nGzVzuJwHDySmFBh9i1W/q358G4HPmBBRBpsoZwvM+qIXGTCi6lwTYGgByDhdWM/YGUD2tNcCAuAWb3SHCAehYI1Q7WoYM9yoOChhQY2hgM7WgIlxCyAdq/KQQesU8NU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783498446; c=relaxed/simple; bh=x418iU5Cq/9eU+LbGTYZWQWhKd/xeQGYHzYWG5YyWeM=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=kequ6/uQ58KGUJzbhFl+TwkWovWJnSPp+CsV6vfnVXovsrMuxxXBSX8KOP5sQl9eH+v17ls4N3log+HiZDbRZc6bFeuEQDlk3EUwyCsA+AGcSSKSVbx3jf0DsyZPA9Kga6KDh6qL6AxwbPuyo1DU7hE6omQJQjUbscs7Fewuqsk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IX242eml; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="IX242eml" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6831E1F000E9; Wed, 8 Jul 2026 08:14:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783498443; bh=pd5YFDi6UtFNx7LiXISEZNdzTbmhPPF0AdqG9vO9H3Q=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IX242emld5TAuVK1kMFIfjuZhKSsVUj6RwEZ/L5vLSbMhrB4kmpFWqHgDq/iuj1II leIy3EJECToPY1d7qSfSfcU2r954ljUCuVaeXQmrBgJSj3K+2mWn3OTLvb7ZEaNAW2 FOOsBMfS466gLinqOc8ML8/ZX/sv3aoFtXy1dGaL8ZuQaiZlI9hKEAlJ0RxbjTFLHs gOHwkJAfORP+sPgbLLkw9o1QlIsGcAo3A8QXsBwDINRbTRnCjcBTigQKVpJFa34PlY tmw6tQENKh5HqtN+W2MeOVTSsQSw76WSd4E/xC7H1SunteXxhWHL2DJrzPW3E1CnHa nyfm5mm6vcjPA== Message-ID: <9e2c389b-ae96-40bb-8edd-5f8a68b571df@kernel.org> Date: Wed, 8 Jul 2026 10:13:58 +0200 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 v4] virtio_balloon: prime stats vq after virtio_device_ready() To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Adam Litke , Rusty Russell , virtualization@lists.linux.dev References: <135278ef075f563ca5b0f3a40e2afcfeb7454f99.1783457622.git.mst@redhat.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS5EYXZpZCBIaWxk ZW5icmFuZCAoQ3VycmVudCkgPGRhdmlkQGtlcm5lbC5vcmc+wsGQBBMBCAA6AhsDBQkmWAik AgsJBBUKCQgCFgICHgUCF4AWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaYJt/AIZAQAKCRBN 3hD3AP+DWriiD/9BLGEKG+N8L2AXhikJg6YmXom9ytRwPqDgpHpVg2xdhopoWdMRXjzOrIKD g4LSnFaKneQD0hZhoArEeamG5tyo32xoRsPwkbpIzL0OKSZ8G6mVbFGpjmyDLQCAxteXCLXz ZI0VbsuJKelYnKcXWOIndOrNRvE5eoOfTt2XfBnAapxMYY2IsV+qaUXlO63GgfIOg8RBaj7x 3NxkI3rV0SHhI4GU9K6jCvGghxeS1QX6L/XI9mfAYaIwGy5B68kF26piAVYv/QZDEVIpo3t7 /fjSpxKT8plJH6rhhR0epy8dWRHk3qT5tk2P85twasdloWtkMZ7FsCJRKWscm1BLpsDn6EQ4 jeMHECiY9kGKKi8dQpv3FRyo2QApZ49NNDbwcR0ZndK0XFo15iH708H5Qja/8TuXCwnPWAcJ DQoNIDFyaxe26Rx3ZwUkRALa3iPcVjE0//TrQ4KnFf+lMBSrS33xDDBfevW9+Dk6IISmDH1R HFq2jpkN+FX/PE8eVhV68B2DsAPZ5rUwyCKUXPTJ/irrCCmAAb5Jpv11S7hUSpqtM/6oVESC 3z/7CzrVtRODzLtNgV4r5EI+wAv/3PgJLlMwgJM90Fb3CB2IgbxhjvmB1WNdvXACVydx55V7 LPPKodSTF29rlnQAf9HLgCphuuSrrPn5VQDaYZl4N/7zc2wcWM7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <135278ef075f563ca5b0f3a40e2afcfeb7454f99.1783457622.git.mst@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/7/26 23:00, Michael S. Tsirkin wrote: > The virtio spec requires the driver not to kick the device before > DRIVER_OK is set. init_vqs() primes the stats virtqueue with a buffer > and kicks the device before virtio_device_ready() is called in > virtballoon_probe(), violating this requirement. > > Further, if the device responds to the early kick by processing the > buffer before DRIVER_OK, stats_request() fires and queues > update_balloon_stats_work. Should probe then fail and free vb, the work > runs against freed memory. > > To fix, move buffer setup to after DRIVER_OK. Be careful to > disable update_balloon_stats_work while this is going on, > to make sure it does not race with the setup. > > Testing: tested that stats still work after the change. > > Fixes: 9564e138b1f6 ("virtio: Add memory statistics reporting to the balloon driver (V4)") > Reported-by: Sashiko:gemini-3.1-pro-preview > Cc: David Hildenbrand > Assisted-by: Claude:claude-sonnet-4-6 > Signed-off-by: Michael S. Tsirkin > > --- > v4: extract stats_update_and_send() helper; call get_buf() before > updating stats buffer in stats_handle_request(). > also ignore add bug failures (never trigger anyway) (reported by sashiko) > v3: add disable_work comment and BUG_ON -> WARN_ON_ONCE (David Hildenbrand) > v2: check that work enable/disable is balanced; explain how add_outbuf > never fails in probe/restore > drivers/virtio/virtio_balloon.c | 67 +++++++++++++++++++-------------- > 1 file changed, 39 insertions(+), 28 deletions(-) > > diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c > index 088b3a0e6ce6..4c4b9bea4356 100644 > --- a/drivers/virtio/virtio_balloon.c > +++ b/drivers/virtio/virtio_balloon.c > @@ -417,6 +417,17 @@ static unsigned int update_balloon_stats(struct virtio_balloon *vb) > return idx; > } > > +static void stats_update_and_send(struct virtio_balloon *vb) > +{ > + struct scatterlist sg; > + unsigned int num_stats; Could do const unsigned int num_stats = update_balloon_stats(vb); LGTM. -- Cheers, David