Message-ID: <CAA85sZuROGN2Nb5We6g99czgjfkJ36Vz5MjC=cOYrU3A8v4TmQ@mail.gmail.com>
Date: Thu, 27 Feb 2025 15:36:26 +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>
Subject: Re: [6.12.15][be2net?] Voluntary context switch within RCU read-side
 critical section!

On Thu, Feb 27, 2025 at 3:33 PM Nikolay Aleksandrov <razor@...ckwall.org> wrote:
>
> On 2/27/25 16:31, Ian Kumlien wrote:
> > On Wed, Feb 26, 2025 at 11:28 PM Ian Kumlien <ian.kumlien@...il.com> wrote:
> >>
> >> 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)
> >
> > So, saw that 6.13.5 was released so, fetched that, applied the patch
> > and no more RCU issues in dmesg
> >
> > Will check more on the suspected performance bit as well when i get
> > home later tonight
> >
> > I also understand Sathya Perla's motivation in saving power on this
> > but things around it have been changed
> > and it no longer works as intended....
> >
>
> Nice, that's good to hear. Wrt the motivation - sure it's ok, but the code was wrong
> if they still want to achieve it, they need to work on an alternative solution.
> We shouldn't keep broken code around.

Agreed, but also, was it broken in 4.7 ;)

Anyway, seems faster from what i can test here so
Tested-by: Ian Kumlien <ian.kumlien@...il.com>

etc etc

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