Re: [Xen-devel] [PATCH] xen-blkback: free requests on disconnection

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 07/09/15 a les 13.35, Bob Liu ha escrit:
> 
> On 09/07/2015 07:10 PM, Julien Grall wrote:
>> On 07/09/15 07:07, Bob Liu wrote:
>>> Hi Julien,
>>
>> Hi Bob,
>>
>>> On 09/04/2015 09:51 PM, Julien Grall wrote:
>>>> Hi Roger,
>>>>
>>>> On 04/09/15 11:08, Roger Pau Monne wrote:
>>>>> Request allocation has been moved to connect_ring, which is called every
>>>>> time blkback connects to the frontend (this can happen multiple times 
>>>>> during
>>>>> a blkback instance life cycle). On the other hand, request freeing has not
>>>>> been moved, so it's only called when destroying the backend instance. Due 
>>>>> to
>>>>> this mismatch, blkback can allocate the request pool multiple times, 
>>>>> without
>>>>> freeing it.
>>>>>
>>>>> In order to fix it, move the freeing of requests to xen_blkif_disconnect 
>>>>> to
>>>>> restore the symmetry between request allocation and freeing.
>>>>>
>>>>> Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
>>>>> Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
>>>>> Cc: Julien Grall <julien.grall@xxxxxxxxxx>
>>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
>>>>> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>>>>> Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
>>>>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
>>>>
>>>> The patch is fixing my problem when using UEFI in the guest. Thank you!
>>>>
>>>
>>> Could you please explain the problem you met a bit more?
>>> So that I can know back port this patch if met similar issue.
>>
>> This is related to commit 86839c56dee28c315a4c19b7bfee450ccd84cd25
>> "xen/block: add multi-page ring support" (Roger, it may be worth to
>> indicate the offending commit in you commit message).
>>
>> When starting a guest using UEFI. After the domain is destroyed I get
>> the following warning from blkback:
>>
>>
>> ------------[ cut here ]------------
>> WARNING: CPU: 2 PID: 95 at
>> /home/julien/works/linux/drivers/block/xen-blkback/xenbus.c:274
>> xen_blkif_deferred_free+0x1f4/0x1f8()
>> Modules linked in:
>> CPU: 2 PID: 95 Comm: kworker/2:1 Tainted: G        W       4.2.0 #85
>> Hardware name: APM X-Gene Mustang board (DT)
>> Workqueue: events xen_blkif_deferred_free
>> Call trace:
>> [<ffff8000000890a8>] dump_backtrace+0x0/0x124
>> [<ffff8000000891dc>] show_stack+0x10/0x1c
>> [<ffff8000007653bc>] dump_stack+0x78/0x98
>> [<ffff800000097e88>] warn_slowpath_common+0x9c/0xd4
>> [<ffff800000097f80>] warn_slowpath_null+0x14/0x20
>> [<ffff800000557a0c>] xen_blkif_deferred_free+0x1f0/0x1f8
>> [<ffff8000000ad020>] process_one_work+0x160/0x3b4
>> [<ffff8000000ad3b4>] worker_thread+0x140/0x494
>> [<ffff8000000b2e34>] kthread+0xd8/0xf0
>> ---[ end trace 6f859b7883c88cdd ]---
>>
>> This is because the allocation of the requests are done during the
>> connection but the free is done when the domain is destroyed. Therefore
>> if the domain is re-initializing the connection (because UEFI or PV Grub
>> is used), the request won't be free and kept until the end.
>>
> 
> Thank you!
> Roger, I think it's better to have this information in your commit message 
> too.

Konrad, would you like me to resend the patch with the modified commit
message, or do you plan to amend it yourself while committing?

Roger.


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