linux-kernel - Re: [PATCH v3 1/2] rcutorture: Perform more frequent testing of ->gpwrap

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Message-ID: <78c902f2-3b01-49ce-85c0-3c748fa43224@paulmck-laptop>
Date: Thu, 10 Apr 2025 18:47:34 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: linux-kernel@...r.kernel.org, Frederic Weisbecker <frederic@...nel.org>,
	Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>, rcu@...r.kernel.org
Subject: Re: [PATCH v3 1/2] rcutorture: Perform more frequent testing of
 ->gpwrap

On Thu, Apr 10, 2025 at 11:54:13AM -0700, Paul E. McKenney wrote:
> On Thu, Apr 10, 2025 at 11:29:03AM -0700, Paul E. McKenney wrote:
> > On Thu, Apr 10, 2025 at 11:03:27AM -0400, Joel Fernandes wrote: >
> > Currently, the ->gpwrap is not tested (at all per my testing) due to
> > the > requirement of a large delta between a CPU's rdp->gp_seq and its
> > node's > rnp->gpseq.  > > This results in no testing of ->gpwrap being
> > set. This patch by default > adds 5 minutes of testing with ->gpwrap
> > forced by lowering the delta > between rdp->gp_seq and rnp->gp_seq to
> > just 8 GPs. All of this is > configurable, including the active time for
> > the setting and a full > testing cycle.  > > By default, the first 25
> > minutes of a test will have the _default_ > behavior there is right now
> > (ULONG_MAX / 4) delta. Then for 5 minutes, > we switch to a smaller delta
> > causing 1-2 wraps in 5 minutes. I believe > this is reasonable since we
> > at least add a little bit of testing for > usecases where ->gpwrap is set.
> > > > Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> > 
> > Much better, thank you!
> > 
> > One potential nit below.  I will run some tests on this version.
> 
> And please feel free to apply the following to both:
> 
> Tested-by: Paul E. McKenney <paulmck@...nel.org>

And this happy situation lasted only until I rebased onto v6.15-rc1 and
on top of this commit:

1342aec2e442 ("Merge branches 'rcu/misc-for-6.16', 'rcu/seq-counters-for-6.16' and 'rcu/torture-for-6.16' into rcu/for-next")

This got me the splat shown below when running rcutorture scenario SRCU-N.
I reverted this commit and tests pass normally.

Your other commit (ARM64 images) continues working fine.

							Thanx, Paul

------------------------------------------------------------------------

[   15.911885] BUG: kernel NULL pointer dereference, address: 0000000000000000
[   15.912413] #PF: supervisor instruction fetch in kernel mode
[   15.912826] #PF: error_code(0x0010) - not-present page
[   15.913218] PGD 0 P4D 0 
[   15.913420] Oops: Oops: 0010 [#1] SMP PTI
[   15.913715] CPU: 3 UID: 0 PID: 62 Comm: rcu_torture_sta Not tainted 6.15.0-rc1-00047-g6e14cad86633 #19 PREEMPT(undef) 
[   15.914535] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.15.0-1 04/01/2014
[   15.915147] RIP: 0010:0x0
[   15.915348] Code: Unable to access opcode bytes at 0xffffffffffffffd6.
[   15.915856] RSP: 0000:ffffa0380021fdc8 EFLAGS: 00010246
[   15.916256] RAX: 0000000000000000 RBX: ffffffffb6b02cc0 RCX: 000000000000000a
[   15.916802] RDX: 0000000000000000 RSI: ffff9f121f418cc0 RDI: 0000000000000000
[   15.917305] RBP: 0000000000000000 R08: ffff9f121f418d20 R09: 0000000000000000
[   15.917789] R10: 0000000000000000 R11: 0000000000000005 R12: ffffffffb6b02d20
[   15.918293] R13: 0000000000000000 R14: ffffa0380021fe50 R15: ffffa0380021fdf8
[   15.918801] FS:  0000000000000000(0000) GS:ffff9f1268a96000(0000) knlGS:0000000000000000
[   15.919313] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   15.919628] CR2: ffffffffffffffd6 CR3: 0000000017c32000 CR4: 00000000000006f0
[   15.920004] Call Trace:
[   15.920139]  <TASK>
[   15.920256]  rcu_torture_stats_print+0x16b/0x670
[   15.920514]  ? __switch_to_asm+0x39/0x70
[   15.920719]  ? finish_task_switch.isra.0+0x76/0x250
[   15.920982]  ? __pfx_rcu_torture_stats+0x10/0x10
[   15.921222]  rcu_torture_stats+0x25/0x70
[   15.921435]  kthread+0xf1/0x1e0
[   15.921602]  ? __pfx_kthread+0x10/0x10
[   15.921797]  ? __pfx_kthread+0x10/0x10
[   15.922000]  ret_from_fork+0x2f/0x50
[   15.922193]  ? __pfx_kthread+0x10/0x10
[   15.922395]  ret_from_fork_asm+0x1a/0x30
[   15.922605]  </TASK>
[   15.922723] Modules linked in:
[   15.922890] CR2: 0000000000000000
[   15.923072] ---[ end trace 0000000000000000 ]---