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From:   Michael Kelley <mikelley@microsoft.com>
To:     vkuznets <vkuznets@redhat.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
CC:     Andres Beltran <lkmlabelt@gmail.com>,
        "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>,
        Dexuan Cui <decui@microsoft.com>, Wei Liu <wei.liu@kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] Drivers: hv: vmbus: Fix kernel crash upon unbinding a
 device from uio_hv_generic driver
Thread-Topic: [PATCH] Drivers: hv: vmbus: Fix kernel crash upon unbinding a
 device from uio_hv_generic driver
Thread-Index: AQHXnnYBTI4PTSpBKkqF5K5fFbYk7KuQ/Vyg
Date:   Thu, 2 Sep 2021 17:09:08 +0000
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References: <20210831143916.144983-1-vkuznets@redhat.com>
In-Reply-To: <20210831143916.144983-1-vkuznets@redhat.com>
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From: Vitaly Kuznetsov <vkuznets@redhat.com> Sent: Tuesday, August 31, 2021=
 7:39 AM
>=20
> The following crash happens when a never-used device is unbound from
> uio_hv_generic driver:
>=20
>  kernel BUG at mm/slub.c:321!
>  invalid opcode: 0000 [#1] SMP PTI
>  CPU: 0 PID: 4001 Comm: bash Kdump: loaded Tainted: G               X ---=
------ ---  5.14.0-0.rc2.23.el9.x86_64 #1
>  Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BI=
OS 090008  12/07/2018
>  RIP: 0010:__slab_free+0x1d5/0x3d0
> ...
>  Call Trace:
>   ? pick_next_task_fair+0x18e/0x3b0
>   ? __cond_resched+0x16/0x40
>   ? vunmap_pmd_range.isra.0+0x154/0x1c0
>   ? __vunmap+0x22d/0x290
>   ? hv_ringbuffer_cleanup+0x36/0x40 [hv_vmbus]
>   kfree+0x331/0x380
>   ? hv_uio_remove+0x43/0x60 [uio_hv_generic]
>   hv_ringbuffer_cleanup+0x36/0x40 [hv_vmbus]
>   vmbus_free_ring+0x21/0x60 [hv_vmbus]
>   hv_uio_remove+0x4f/0x60 [uio_hv_generic]
>   vmbus_remove+0x23/0x30 [hv_vmbus]
>   __device_release_driver+0x17a/0x230
>   device_driver_detach+0x3c/0xa0
>   unbind_store+0x113/0x130
> ...
>=20
> The problem appears to be that we free 'ring_info->pkt_buffer' twice:
> first, when the device is unbound from in-kernel driver (netvsc in this
> case) and second from hv_uio_remove(). Normally, ring buffer is supposed
> to be re-initialized from hv_uio_open() but this happens when UIO device
> is being opened and this is not guaranteed to happen.
>=20
> Generally, it is OK to call hv_ringbuffer_cleanup() twice for the same
> channel (which is being handed over between in-kernel drivers and UIO) ev=
en
> if we didn't call hv_ringbuffer_init() in between. We, however, need to
> avoid kfree() call for an already freed pointer.
>=20
> Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V ou=
t of the ring buffer")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  drivers/hv/ring_buffer.c | 1 +
>  1 file changed, 1 insertion(+)
>=20
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 2aee356840a2..314015d9e912 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -245,6 +245,7 @@ void hv_ringbuffer_cleanup(struct hv_ring_buffer_info=
 *ring_info)
>  	mutex_unlock(&ring_info->ring_buffer_mutex);
>=20
>  	kfree(ring_info->pkt_buffer);
> +	ring_info->pkt_buffer =3D NULL;
>  	ring_info->pkt_buffer_size =3D 0;
>  }
>=20
> --
> 2.31.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>