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Date:   Thu, 10 Aug 2023 21:54:16 +0000
From:   Joel Fernandes <joel@joelfernandes.org>
To:     "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, patches@lists.linux.dev,
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Subject: Re: [PATCH 5.15 00/92] 5.15.126-rc1 review
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On Thu, Aug 10, 2023 at 10:55:16AM -0700, Paul E. McKenney wrote:
> On Wed, Aug 09, 2023 at 02:45:44PM -0700, Guenter Roeck wrote:
> > On 8/9/23 13:39, Joel Fernandes wrote:
> > > On Wed, Aug 9, 2023 at 4:38 PM Guenter Roeck <linux@roeck-us.net> wrote:
> > > > 
> > > > On 8/9/23 13:14, Joel Fernandes wrote:
> > > > > On Wed, Aug 09, 2023 at 12:25:48PM -0700, Guenter Roeck wrote:
> > > > > > On Wed, Aug 09, 2023 at 02:35:59PM -0400, Joel Fernandes wrote:
> > > > > > > On Wed, Aug 9, 2023 at 12:18 PM Guenter Roeck <linux@roeck-us.net> wrote:
> > > > > > > > 
> > > > > > > > On 8/9/23 06:53, Joel Fernandes wrote:
> > > > > > > > > On Wed, Aug 09, 2023 at 12:40:36PM +0200, Greg Kroah-Hartman wrote:
> > > > > > > > > > This is the start of the stable review cycle for the 5.15.126 release.
> > > > > > > > > > There are 92 patches in this series, all will be posted as a response
> > > > > > > > > > to this one.  If anyone has any issues with these being applied, please
> > > > > > > > > > let me know.
> > > > > > > > > > 
> > > > > > > > > > Responses should be made by Fri, 11 Aug 2023 10:36:10 +0000.
> > > > > > > > > > Anything received after that time might be too late.
> > > > > > > > > > 
> > > > > > > > > > The whole patch series can be found in one patch at:
> > > > > > > > > >        https://www.kernel.org/pub/linux/kernel/v5.x/stable-review/patch-5.15.126-rc1.gz
> > > > > > > > > > or in the git tree and branch at:
> > > > > > > > > >        git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git linux-5.15.y
> > > > > > > > > > and the diffstat can be found below.
> > > > > > > > > 
> > > > > > > > > Not necesscarily new with 5.15 stable but 3 of the 19 rcutorture scenarios
> > > > > > > > > hang with this -rc: TREE04, TREE07, TASKS03.
> > > > > > > > > 
> > > > > > > > > 5.15 has a known stop machine issue where it hangs after 1.5 hours with cpu
> > > > > > > > > hotplug rcutorture testing. Me and tglx are continuing to debug this. The
> > > > > > > > > issue does not show up on anything but 5.15 stable kernels and neither on
> > > > > > > > > mainline.
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > Do you by any have a crash pattern that we could possibly use to find the crash
> > > > > > > > in ChromeOS crash logs ? No idea if that would help, but it could provide some
> > > > > > > > additional data points.
> > > > > > > 
> > > > > > > The pattern shows as a hard hang, the system is unresponsive and all CPUs
> > > > > > > are stuck in stop_machine. Sometimes it recovers on its own from the
> > > > > > > hang and then RCU immediately gives stall warnings. It takes 1.5 hour
> > > > > > > to reproduce and sometimes never happens for several hours.
> > > > > > > 
> > > > > > > It appears related to CPU hotplug since gdb showed me most of the CPUs
> > > > > > > are spinning in multi_cpu_stop() / stop machine after the hang.
> > > > > > > 
> > > > > > 
> > > > > > Hmm, we do see lots of soft lockups with multi_cpu_stop() in the backtrace,
> > > > > > but not with v5.15.y but with v5.4.y. The actual hang is in stop_machine_yield().
> > > > > 
> > > > > Interesting. It looks similar as far as the stack dump in gdb goes, here are
> > > > > the stacks I dumped with the hang I referred to:
> > > > > https://paste.debian.net/1288308/
> > > > > 
> > > > 
> > > > That link gives me "Entry not found".
> > > 
> > > Yeah that was weird. Here it is again: https://pastebin.com/raw/L3nv1kH2
> > 
> > I found a couple of crash reports from chromeos-5.10, one of them complaining
> > about RCU issues. I sent you links via IM. Nothing from 5.15 or later, though.
> 
> Is the crash showing the eternally refiring timer fixed by this commit?
> 
> 53e87e3cdc15 ("timers/nohz: Last resort update jiffies on nohz_full IRQ entry")

Ah I was just replying, I have been seeing really good results after applying
the following 3 commits since yesterday:

53e87e3cdc15 ("timers/nohz: Last resort update jiffies on nohz_full IRQ entry")
5417ddc1cf1f ("timers/nohz: Switch to ONESHOT_STOPPED in the low-res handler when the tick is stopped")
a1ff03cd6fb9 ("tick: Detect and fix jiffies update stall")

5417ddc1cf1f also mentioned a "tick storm" which is exactly what I was
seeing.

I did a lengthy test and everything is looking good. I'll send these out to
the stable list.

thanks,

 - Joel