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Y. Srinivasan" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Drivers: hv: vmbus: Fix kernel crash upon unbinding a device from uio_hv_generic driver Message-ID: <20210901112500.7q4oxjtesiuniop3@liuwe-devbox-debian-v2> References: <20210831143916.144983-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210831143916.144983-1-vkuznets@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 31, 2021 at 04:39:16PM +0200, Vitaly Kuznetsov wrote: > The following crash happens when a never-used device is unbound from > uio_hv_generic driver: > > 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, BIOS 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 > ... > > 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. > > 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) even > if we didn't call hv_ringbuffer_init() in between. We, however, need to > avoid kfree() call for an already freed pointer. > > Fixes: adae1e931acd ("Drivers: hv: vmbus: Copy packets sent by Hyper-V out of the ring buffer") > Signed-off-by: Vitaly Kuznetsov > --- > drivers/hv/ring_buffer.c | 1 + > 1 file changed, 1 insertion(+) > > 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); > > kfree(ring_info->pkt_buffer); > + ring_info->pkt_buffer = NULL; This certainly won't hurt. I would however like to wait till Andrea and Michael go over the reasoning of this patch before doing anything. Wei. > ring_info->pkt_buffer_size = 0; > } > > -- > 2.31.1 >