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From: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
To: Greg KH <greg@kroah.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
	dledford@redhat.com, linux-rdma@vger.kernel.org,
	Kaike Wan <kaike.wan@intel.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH for-rc 1/4] IB/hfi1: Call xa_destroy before freeing dummy_netdev
Date: Thu, 1 Apr 2021 11:00:19 -0400
Message-ID: <b44629f3-c091-3485-4608-c9eef2f7ce18@cornelisnetworks.com> (raw)
In-Reply-To: <YGXUu88J811vV+p8@kroah.com>

On 4/1/2021 10:12 AM, Greg KH wrote:
> On Thu, Apr 01, 2021 at 10:02:30AM -0400, Dennis Dalessandro wrote:
>> On 4/1/2021 2:06 AM, Greg KH wrote:
>>> On Wed, Mar 31, 2021 at 03:36:14PM -0400, Dennis Dalessandro wrote:
>>>> On 3/29/2021 10:09 AM, Jason Gunthorpe wrote:
>>>>> On Mon, Mar 29, 2021 at 09:48:17AM -0400, dennis.dalessandro@cornelisnetworks.com wrote:
>>>>>
>>>>>> diff --git a/drivers/infiniband/hw/hfi1/netdev_rx.c b/drivers/infiniband/hw/hfi1/netdev_rx.c
>>>>>> index 2c8bc02..cec02e8 100644
>>>>>> +++ b/drivers/infiniband/hw/hfi1/netdev_rx.c
>>>>>> @@ -372,7 +372,11 @@ int hfi1_netdev_alloc(struct hfi1_devdata *dd)
>>>>>>     void hfi1_netdev_free(struct hfi1_devdata *dd)
>>>>>>     {
>>>>>>     	if (dd->dummy_netdev) {
>>>>>> +		struct hfi1_netdev_priv *priv =
>>>>>> +			hfi1_netdev_priv(dd->dummy_netdev);
>>>>>> +
>>>>>>     		dd_dev_info(dd, "hfi1 netdev freed\n");
>>>>>> +		xa_destroy(&priv->dev_tbl);
>>>>>>     		kfree(dd->dummy_netdev);
>>>>>>     		dd->dummy_netdev = NULL;
>>>>>
>>>>> This is doing kfree() on a struct net_device?? Huh?
>>>>>
>>>>> You should have put this in your own struct and used container_of not
>>>>> co-oped netdev_priv, then free your own struct.
>>>>>
>>>>> It is a bit weird to see a xa_destroy like this, how did things get ot
>>>>> the point that no concurrent thread can see the xarray but there is
>>>>> still stuff stored in it?
>>>>>
>>>>> And it is weird this is storing two different types in it too, with no
>>>>> refcounting..
>>>>
>>>> We do rework this stuff in the other patch series.
>>>>
>>>> https://patchwork.kernel.org/project/linux-rdma/patch/1617026056-50483-11-git-send-email-dennis.dalessandro@cornelisnetworks.com/
>>>>
>>>> If we fix it up in the for-next series, what should we do about stable?
>>>
>>> What does stable matter?  WHy can it not just take the same patches that
>>> end up in Linus's tree?
>>
>> Guess it's more of a general question. What is the best way to handle things
>> if the code changes drastically in Linus' tree, to the point where the bug
>> no longer exists there, but does in stable?
> 
> Documentation/process/stable-kernel-rules.rst should be your first stop
> for stuff like this.  Why not just take those "drastic changes" into the
> stable kernel as well?

Yep, indeed it was my first stop :) and right at the top, it cannot be 
bigger than 100 lines, must fix only one thing, etc etc. That's what got 
me wondering about all this.

> If for some reason that is impossible, then just email a patch to stable
> and document the heck out of why this is not in Linus's tree and what
> you have done to ensure that this change is correct.  And get the
> maintainer to agree.  And be ready to fix it up again afterward as 90%
> of the time we do this, the "new patch" causes problems :)

Makes total sense. Definitely not the route we want to take, and not 
applicable for this current patch anyway.

Appreciate the advice!

-Denny


  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-29 13:48 [PATCH for-rc 0/4] hfi fixes dennis.dalessandro
2021-03-29 13:48 ` [PATCH for-rc 1/4] IB/hfi1: Call xa_destroy before freeing dummy_netdev dennis.dalessandro
2021-03-29 14:09   ` Jason Gunthorpe
2021-03-31 19:36     ` Dennis Dalessandro
2021-04-01  6:06       ` Greg KH
2021-04-01 14:02         ` Dennis Dalessandro
2021-04-01 14:12           ` Greg KH
2021-04-01 15:00             ` Dennis Dalessandro [this message]
2021-04-01 12:33       ` Jason Gunthorpe
2021-04-01 13:42         ` Wan, Kaike
2021-04-01 13:48           ` Jason Gunthorpe
2021-03-29 13:48 ` [PATCH for-rc 2/4] IB/hfi1: Call xa_destroy before unloading the module dennis.dalessandro
2021-03-29 14:11   ` Jason Gunthorpe
2021-04-08 13:30     ` Dennis Dalessandro
2021-03-29 13:48 ` [PATCH for-rc 3/4] IB/hfi1: Fix probe time panic when AIP is enabled with a buggy BIOS dennis.dalessandro
2021-04-07 23:04   ` Jason Gunthorpe
2021-03-29 13:48 ` [PATCH for-rc 4/4] IB/hfi1: Fix regressions in security fix dennis.dalessandro
2021-03-29 18:36   ` Ira Weiny
2021-04-07 18:33     ` Jason Gunthorpe
2021-04-07 20:20       ` Dennis Dalessandro
2021-04-13 22:55   ` Jason Gunthorpe

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