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From: Michael Tokarev <mjt@tls.msk.ru>
To: Li Qiang <liq3ea@163.com>,
	mst@redhat.com, kraxel@redhat.com, dmitry.fleytman@gmail.com,
	jasowang@redhat.com, alxndr@bu.edu, peter.maydell@linaro.org,
	pbonzini@redhat.com
Cc: liq3ea@gmail.com, qemu-devel@nongnu.org
Subject: Re: [RFC 3/3] virtio-gpu: make the IO handler reentrant
Date: Thu, 3 Sep 2020 08:12:35 +0300	[thread overview]
Message-ID: <01e9f449-00c8-5a9d-b212-4df0147b6e5c@msgid.tls.msk.ru> (raw)
In-Reply-To: <20200902162206.101872-4-liq3ea@163.com>

02.09.2020 19:22, Li Qiang wrote:
..
> @@ -809,6 +809,10 @@ void virtio_gpu_process_cmdq(VirtIOGPU *g)
>  {
>      struct virtio_gpu_ctrl_command *cmd;
>  
> +    if (atomic_read(&g->in_io)) {
> +        return;
> +    }
> +    atomic_set(&g->in_io, 1);

Can't we race in these two instructions? Both
threads atomic_reads at the same time, both see zero,
and both are trying to set it to 1, no?

Just asking really, b/c despite of the atomic_ prefix,
to me this look a bit unsafe..

Thanks,

/mjt


  reply	other threads:[~2020-09-03  5:16 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-02 16:22 [RFC 0/3] try to solve the DMA to MMIO issue Li Qiang
2020-09-02 16:22 ` [RFC 1/3] e1000e: make the IO handler reentrant Li Qiang
2020-09-02 16:22 ` [RFC 2/3] xhci: " Li Qiang
2020-09-02 16:22 ` [RFC 3/3] virtio-gpu: " Li Qiang
2020-09-03  5:12   ` Michael Tokarev [this message]
2020-09-03 10:32     ` Li Qiang
2020-09-03  3:54 ` [RFC 0/3] try to solve the DMA to MMIO issue Jason Wang
2020-09-03  4:06   ` Alexander Bulekov
2020-09-03  4:24     ` Jason Wang
2020-09-03  4:50       ` Li Qiang
2020-09-03  6:16         ` Jason Wang
2020-09-03  6:28           ` Li Qiang
2020-09-03 10:53   ` Peter Maydell
2020-09-03 11:11     ` Li Qiang
2020-09-03 11:19       ` Peter Maydell
2020-09-03 11:23         ` Li Qiang
2020-09-03 11:28           ` Peter Maydell
2020-09-03 13:35             ` Philippe Mathieu-Daudé
2020-09-03 13:41               ` Peter Maydell
2020-09-04  2:45         ` Jason Wang

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