netdev - Re: [6.12.15][be2net?] Voluntary context switch within RCU read-side critical section!

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Message-ID: <ed6723e3-4e47-4dac-bc42-b65f7d42cbea@blackwall.org>
Date: Wed, 26 Feb 2025 14:00:13 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Ian Kumlien <ian.kumlien@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
 Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: [6.12.15][be2net?] Voluntary context switch within RCU read-side
 critical section!

On 2/26/25 13:52, Ian Kumlien wrote:
> On Wed, Feb 26, 2025 at 11:33 AM Nikolay Aleksandrov
> <razor@...ckwall.org> wrote:
>>
>> On 2/26/25 11:55, Ian Kumlien wrote:
>>> On Wed, Feb 26, 2025 at 10:24 AM Ian Kumlien <ian.kumlien@...il.com> wrote:
>>>>
>>>> On Wed, Feb 26, 2025 at 2:05 AM Jakub Kicinski <kuba@...nel.org> wrote:
>>>>>
>>>>> On Tue, 25 Feb 2025 11:13:47 +0100 Ian Kumlien wrote:
>>>>>> Same thing happens in 6.13.4, FYI
>>>>>
>>>>> Could you do a minor bisection? Does it not happen with 6.11?
>>>>> Nothing jumps out at quick look.
>>>>
>>>> I have to admint that i haven't been tracking it too closely until it
>>>> turned out to be an issue
>>>> (makes network traffic over wireguard, through that node very slow)
>>>>
>>>> But i'm pretty sure it was ok in early 6.12.x - I'll try to do a bisect though
>>>> (it's a gw to reach a internal server network in the basement, so not
>>>> the best setup for this)
>>>
>>> Since i'm at work i decided to check if i could find all the boot
>>> logs, which is actually done nicely by systemd
>>> first known bad: 6.11.7-300.fc41.x86_64
>>> last known ok: 6.11.6-200.fc40.x86_64
>>>
>>> Narrows the field for a bisect at least, =)
>>>
>>
>> Saw bridge, took a look. :)
>>
>> I think there are multiple issues with benet's be_ndo_bridge_getlink()
>> because it calls be_cmd_get_hsw_config() which can sleep in multiple
>> places, e.g. the most obvious is the mutex_lock() in the beginning of
>> be_cmd_get_hsw_config(), then we have the call trace here which is:
>> be_cmd_get_hsw_config -> be_mcc_notify_wait -> be_mcc_wait_compl -> usleep_range()
>>
>> Maybe you updated some tool that calls down that path along with the kernel and system
>> so you started seeing it in Fedora 41?
> 
> Could be but it's pretty barebones
> 
>> IMO this has been problematic for a very long time, but obviously it depends on the
>> chip type. Could you share your benet chip type to confirm the path?
> 
> I don't know how to find the actual chip information but it's identified as:
> Emulex Corporation OneConnect NIC (Skyhawk) (rev 10)
> 

Good, that confirms it. The skyhawk chip falls in the "else" of the block in
be_ndo_bridge_getlink() which calls be_cmd_get_hsw_config().

>> For the blamed commit I'd go with:
>>  commit b71724147e73
>>  Author: Sathya Perla <sathya.perla@...adcom.com>
>>  Date:   Wed Jul 27 05:26:18 2016 -0400
>>
>>      be2net: replace polling with sleeping in the FW completion path
>>
>> This one changed the udelay() (which is safe) to usleep_range() and the spinlock
>> to a mutex.
> 
> So, first try will be to try without that patch then, =)
> 

That would be a good try, yes. It is not a straight-forward revert though since a lot
of changes have happened since that commit. Let me know if you need help with that,
I can prepare the revert to test.

>> Cheers,
>>  Nik
>>