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

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Message-ID: <CAA85sZutt0Eydh4B5AUb2xgvPkPF2Wa2yU4iXprgmRFPVM5qUQ@mail.gmail.com>
Date: Wed, 26 Feb 2025 23:28:38 +0100
From: Ian Kumlien <ian.kumlien@...il.com>
To: Nikolay Aleksandrov <razor@...ckwall.org>
Cc: Jakub Kicinski <kuba@...nel.org>, 
	Linux Kernel Network Developers <netdev@...r.kernel.org>, Sathya Perla <sathya.perla@...adcom.com>
Subject: Re: [6.12.15][be2net?] Voluntary context switch within RCU read-side
 critical section!

On Wed, Feb 26, 2025 at 2:11 PM Nikolay Aleksandrov <razor@...ckwall.org> wrote:
>
> On 2/26/25 14:26, Ian Kumlien wrote:
> > On Wed, Feb 26, 2025 at 1:00 PM Nikolay Aleksandrov <razor@...ckwall.org> wrote:
> >>
> >> 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.
> >
> > Yeah, looked at the size of it and... well... I dunno if i'd have the time =)
> >
>
> Can you try the attached patch?
> It is on top of net-next (but also applies to Linus' tree):
>  git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git
>
> It partially reverts the mentioned commit above (only mutex -> spinlock and usleep -> udelay)
> because the commit does many more things.
>
> Also +CC original patch author which I forgot to do.

Thanks, built and installed but it refuses to boot it - will have to
check during the weekend...
(boots the latest fedora version even if this one is the selected one
according to grubby)

> Thanks,
>  Nik
>