netdev - Re: [Intel-wired-lan] [PATCH] [PATCH iwl-net] idpf: Acquire the lock before accessing the xn->salt

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Message-ID: <4bea2987-e399-4579-90b3-58260297feb5@intel.com>
Date: Wed, 7 Aug 2024 16:04:24 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Manoj Vishwanathan <manojvishy@...gle.com>
CC: <netdev@...r.kernel.org>, David Decotigny <decot@...gle.com>,
	<linux-kernel@...r.kernel.org>, Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	<intel-wired-lan@...ts.osuosl.org>
Subject: Re: [Intel-wired-lan] [PATCH] [PATCH iwl-net] idpf: Acquire the lock
 before accessing the xn->salt

From: Manoj Vishwanathan <manojvishy@...gle.com>
Date: Wed, 7 Aug 2024 06:58:59 -0700

> Thanks Przemek & Olek for your quick feedback and responses.
> Hi Olek,
> I can add more details about the issue we faced in the commit message.
> The bug we had here was a virtchnl delay leading to the xn->salt
> mismatch. This could be due to several factors including default CPU
> bounded kworker workqueue for virtchnl message processing being

That's why I always tell people to stop creating more and more private
workqueues and just use the system ones, there's a whole collection for
every need...

> starved by aggressive userspace load causing the virtchnl to be
> delayed. While debugging this issue, this locking order  appeared like
> a potential issue, hence the change was made.
> But, this change is more a clean up we felt based on concurrent access
> to the virtchnl transaction struct and does not fix the issue. This is
> more of the patch to do the right thing before we access the "xn".
> I wanted to start with a first patch to the community for acceptance
> followed by a series of other patches that are general clean up or
> improvements to IDPF in general. Will follow with with [PATCH v3]

Maybe you'd prepare a full series then right away?

I hope it won't conflict much with my tree (but you always can
double-check[0]) (Chapter II is already posted here on IWL and netdev@)

> 
> Thanks,
> Manoj
> 
> On Wed, Aug 7, 2024 at 4:05 AM Alexander Lobakin
> <aleksander.lobakin@...el.com> wrote:
>>
>> From: Manoj Vishwanathan <manojvishy@...gle.com>
>> Date: Mon,  5 Aug 2024 18:21:59 +0000
>>
>>> The transaction salt was being accessed before acquiring the
>>> idpf_vc_xn_lock when idpf has to forward the virtchnl reply.
>>
>> You need to explain in details here what issue you have faced due to
>> that, how to reproduce it and how this fix does help.
>> Otherwise, it's impossible to suggest what is happening and how to test
>> whether the fix is correct.
>>
>>>
>>> Fixes: 34c21fa894a1a (“idpf: implement virtchnl transaction manager”)
>>> Signed-off-by: Manoj Vishwanathan <manojvishy@...gle.com>
>>> ---
>>>  drivers/net/ethernet/intel/idpf/idpf_virtchnl.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
>>> index 70986e12da28..30eec674d594 100644
>>> --- a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
>>> +++ b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
>>> @@ -612,14 +612,15 @@ idpf_vc_xn_forward_reply(struct idpf_adapter *adapter,
>>>               return -EINVAL;
>>>       }
>>>       xn = &adapter->vcxn_mngr->ring[xn_idx];
>>> +     idpf_vc_xn_lock(xn);
>>>       salt = FIELD_GET(IDPF_VC_XN_SALT_M, msg_info);
>>
>> The lock can be taken here after the FIELD_GET(), not before, to reduce
>> the critical/locked section execution time.
>>
>>>       if (xn->salt != salt) {
>>>               dev_err_ratelimited(&adapter->pdev->dev, "Transaction salt does not match (%02x != %02x)\n",
>>>                                   xn->salt, salt);
>>> +             idpf_vc_xn_unlock(xn);
>>>               return -EINVAL;
>>>       }
>>>
>>> -     idpf_vc_xn_lock(xn);
>>>       switch (xn->state) {
>>>       case IDPF_VC_XN_WAITING:
>>>               /* success */
>>
>> Thanks,
>> Olek

[0] https://github.com/alobakin/linux/commits/idpf-libie-new

Thanks,
Olek