Re: [PATCH 6.4 000/227] 6.4.7-rc1 review

[Paul E. McKenney]

On Thu, Jul 27, 2023 at 07:39:54AM -0700, Guenter Roeck wrote:
> On 7/27/23 07:06, Paul E. McKenney wrote:
> > On Thu, Jul 27, 2023 at 09:26:52AM -0400, Joel Fernandes wrote:
> > > 
> > > 
> > > > On Jul 27, 2023, at 7:35 AM, Pavel Machek <pavel@xxxxxxx> wrote:
> > > > 
> > > > Hi!
> > > > 
> > > > > > This is the start of the stable review cycle for the 6.4.7 release.
> > > > > > There are 227 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 Thu, 27 Jul 2023 10:44:26 +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/v6.x/stable-review/patch-6.4.7-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-6.4.y
> > > > > > and the diffstat can be found below.
> > > > > 
> > > > > I saw this when running rcutorture, this one happened in the TREE04
> > > > > configuration. This is likely due to the stuttering issues we are discussing
> > > > > in the other thread. Anyway I am just making a note here while I am
> > > > > continuing to look into it.
> > > > 
> > > > So is the stuttering new in 6.4.7?
> > > 
> > > No it is an old feature in RCU torture tests. But is dependent on timing. Something
> > > changed in recent kernels that is making the issues with it more likely. Its hard to bisect as failure sometimes takes hours.
> > > 
> > > > 
> > > > > Other than that, all tests pass:
> > > > > Tested-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > > > 
> > > > ...or you still believe 6.4.7 is okay to release?
> > > 
> > > As such, it should be Ok. However naturally I am not happy that the RCU testing
> > > is intermittently failing. These issues have been seen in last several 6.4 stable releases
> > > so since those were released, maybe this one can be too?
> > > The fix for stuttering is currently being reviewed.
> > 
> > Or, to look at it another way, the stuttering fix is specific to torture
> > testing.  Would we really want to hold up a -stable release only because
> > rcutorture occasionally gives a false-positive failure on certain types
> > of systems?
> > 
> 
> No. However, (unrelated) in linux-next, rcu tests sometimes result in apparent hangs
> or long runtime.
> 
> [    0.778841] Mount-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
> [    0.779011] Mountpoint-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
> [    0.797998] Running RCU synchronous self tests
> [    0.798209] Running RCU synchronous self tests
> [    0.912368] smpboot: CPU0: AMD Opteron 63xx class CPU (family: 0x15, model: 0x2, stepping: 0x0)
> [    0.923398] RCU Tasks: Setting shift to 2 and lim to 1 rcu_task_cb_adjust=1.
> [    0.925419] Running RCU-tasks wait API self tests
> 
> (hangs until aborted). This is primarily with Opteron CPUs, but also with others such as Haswell,
> Icelake-Server, and pentium3. It is all but impossible to bisect because it doesn't happen
> all the time. All I was able to figure out was that it has to do with rcu changes in linux-next.
> I'd be much more concerned about that.

First I have heard of this, so thank you for letting me know.

About what fraction of the time does this happen?

							Thanx, Paul