linux-kernel - Re: [Regression] wifi problems since tg3 started throwing rcu stall warnings

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Message-ID: <814ca9e3-df3b-45ce-ad36-9659b445c499@paulmck-laptop>
Date: Fri, 8 Nov 2024 07:14:41 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: Mingcong Bai <jeffbai@...c.io>,
	Thorsten Leemhuis <regressions@...mhuis.info>,
	Linux regressions mailing list <regressions@...ts.linux.dev>,
	LKML <linux-kernel@...r.kernel.org>, rcu <rcu@...r.kernel.org>,
	sakiiily@...c.io, Kexy Biscuit <kexybiscuit@...c.io>
Subject: Re: [Regression] wifi problems since tg3 started throwing rcu stall
 warnings

On Fri, Nov 08, 2024 at 02:46:16PM +0100, Frederic Weisbecker wrote:
> Le Fri, Nov 08, 2024 at 12:29:40AM +0800, Mingcong Bai a écrit :
> > Hi Frederic,
> > 
> > <snip>
> > 
> > > Sorry for the lag, I still don't understand how this specific commit
> > > can produce this issue. Can you please retry with and without this
> > > commit
> > > reverted?
> > 
> > Just tested v6.12-rc6 with and without the revert. Without the revert, the
> > touchpad and the wireless adapter both stopped working, whereas with the
> > revert, both devices functions as normal.
> > 
> > I have attached the dmesg for both kernels below. Unlike the log we got last
> > time, there is no direct reference to tg3 any more, but the NMI backtrace
> > still pointed to NetworkManager and net/netlink-related functions (perhaps a
> > debug kernel would be more helpful?). Here's a snippet:
> > 
> > [   10.337720] rcu: INFO: rcu_preempt detected expedited stalls on
> > CPUs/tasks: { P683 } 21 jiffies s: 781 root: 0x0/T
> > [   10.339168] rcu: blocking rcu_node structures (internal RCU debug):
> > [   10.591480] loop0: detected capacity change from 0 to 8
> > [   11.777733] rcu: INFO: rcu_preempt detected expedited stalls on
> > CPUs/tasks: { 3-.... } 21 jiffies s: 1077 root: 0x8/.
> > [   11.779210] rcu: blocking rcu_node structures (internal RCU debug):
> > [   11.780630] Sending NMI from CPU 1 to CPUs 3:
> > [   11.780659] NMI backtrace for cpu 3
> > [   11.780663] CPU: 3 UID: 0 PID: 1027 Comm: NetworkManager Not tainted
> > 6.12.0-aosc-main #1
> 
> Funny, this happens on bootup and no CPU has ever gone offline, so the path
> modified by this patch shouldn't have been taken. And yet this commit has
> an influence to the point of reliably triggering that stall.
> 
> I'm running off of ideas, Paul any clue?

Here is one straw to grasp at...

Is it possible that one of the CPUs had a problem coming online at boot,
and therefore backed out of the online process, thus appearing to at
least some of the CPU-hotplug notifiers to have gone offline?

							Thanx, Paul