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Subject: Re: [PATCH] virtio_ring: Fix mem leak with vring_new_virtqueue()
To:     Jason Wang <jasowang@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>
CC:     Tiwei Bie <tiwei.bie@intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        <virtualization@lists.linux-foundation.org>,
        <linux-kernel@vger.kernel.org>, <linux-remoteproc@vger.kernel.org>
References: <20200224212643.30672-1-s-anna@ti.com>
 <b622c831-9adb-b9af-dd4a-21605bc124a8@redhat.com>
 <0ace3a3b-cf2f-7977-5337-f74f530afbe1@ti.com>
 <1ce2bee4-64ed-f630-2695-8e8b9b8e27c1@redhat.com>
From:   Suman Anna <s-anna@ti.com>
Message-ID: <90f85329-9bec-1204-6a0d-892c92219eb1@ti.com>
Date:   Wed, 26 Feb 2020 11:01:30 -0600
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On 2/25/20 9:13 PM, Jason Wang wrote:
> 
> On 2020/2/26 上午12:51, Suman Anna wrote:
>> Hi Jason,
>>
>> On 2/24/20 11:39 PM, Jason Wang wrote:
>>> On 2020/2/25 上午5:26, Suman Anna wrote:
>>>> The functions vring_new_virtqueue() and __vring_new_virtqueue() are
>>>> used
>>>> with split rings, and any allocations within these functions are
>>>> managed
>>>> outside of the .we_own_ring flag. The commit cbeedb72b97a
>>>> ("virtio_ring:
>>>> allocate desc state for split ring separately") allocates the desc
>>>> state
>>>> within the __vring_new_virtqueue() but frees it only when the
>>>> .we_own_ring
>>>> flag is set. This leads to a memory leak when freeing such allocated
>>>> virtqueues with the vring_del_virtqueue() function.
>>>>
>>>> Fix this by moving the desc_state free code outside the flag and only
>>>> for split rings. Issue was discovered during testing with remoteproc
>>>> and virtio_rpmsg.
>>>>
>>>> Fixes: cbeedb72b97a ("virtio_ring: allocate desc state for split ring
>>>> separately")
>>>> Signed-off-by: Suman Anna<s-anna@ti.com>
>>>> ---
>>>>    drivers/virtio/virtio_ring.c | 4 ++--
>>>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/virtio/virtio_ring.c
>>>> b/drivers/virtio/virtio_ring.c
>>>> index 867c7ebd3f10..58b96baa8d48 100644
>>>> --- a/drivers/virtio/virtio_ring.c
>>>> +++ b/drivers/virtio/virtio_ring.c
>>>> @@ -2203,10 +2203,10 @@ void vring_del_virtqueue(struct virtqueue *_vq)
>>>>                         vq->split.queue_size_in_bytes,
>>>>                         vq->split.vring.desc,
>>>>                         vq->split.queue_dma_addr);
>>>> -
>>>> -            kfree(vq->split.desc_state);
>>>>            }
>>>>        }
>>>> +    if (!vq->packed_ring)
>>>> +        kfree(vq->split.desc_state);
>>> Nitpick, it looks to me it would be more clear if we just free
>>> desc_state unconditionally here (and remove the kfree for packed above).
>> OK, are you sure you want that to be folded into this patch? It looks to
>> me a separate cleanup/consolidation patch, and packed desc_state does
>> not suffer this memleak, and need not be backported into stable kernels.
>>
>> regards
>> Suman
> 
> 
> Though it's just a small tweak, I'm fine for leaving it for future.
> 
> So
> 
> Acked-by: Jason Wang <jasowang@redhat.com>

Thanks Jason, will post a patch for the same once this is merged.

regards
Suman