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Message-ID: <620852c4-c2ae-4242-9996-1af248afba2c@paulmck-laptop>
Date: Thu, 15 May 2025 17:37:03 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: kernel test robot <oliver.sang@...el.com>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com,
Joel Fernandes <joelagnelf@...dia.com>,
Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [paulmckrcu:dev.2025.05.05a] [rcutorture] 54d0803f63:
WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture]
On Wed, May 14, 2025 at 10:23:26AM +0800, kernel test robot wrote:
>
> hi, Paul,
>
> we noticed various issues for both 54d0803f63/parent in this test.
>
> =========================================================================================
> tbox_group/testcase/rootfs/kconfig/compiler/runtime/test/torture_type:
> vm-snb/rcutorture/debian-11.1-i386-20220923.cgz/i386-randconfig-061-20250510/clang-20/300s/default/trivial
>
> ec3f43f72b268d44 54d0803f632b402e519c7d97a6b
> ---------------- ---------------------------
> fail:runs %reproduction fail:runs
> | | |
> :100 71% 71:98 rcutorture.trivial.fail <--- (1)
> :100 71% 71:98 dmesg.EIP:rcu_torture_stats_print <--- (2)
> 94:100 0% 94:98 dmesg.EIP:synchronize_rcu_trivial
> 100:100 -2% 98:98 dmesg.UBSAN:implicit-conversion_in_drivers/firewire/core-transaction.c
> 100:100 -2% 98:98 dmesg.UBSAN:negation-overflow_in_lib/sort.c
> 100:100 -2% 98:98 dmesg.UBSAN:negation-overflow_in_mm/memcontrol.c
> :100 71% 71:98 dmesg.WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture] <--- (3)
> 94:100 0% 94:98 dmesg.WARNING:at_kernel/rcu/rcutorture.c:#synchronize_rcu_trivial[rcutorture]
> 100:100 -2% 98:98 dmesg.boot_failures
>
>
> but seems (1)(2)(3) are quite persistent on 54d0803f63 and clean on parent.
>
>
> Hello,
>
> kernel test robot noticed "WARNING:at_kernel/rcu/rcutorture.c:#rcu_torture_stats_print[rcutorture]" on:
>
> commit: 54d0803f632b402e519c7d97a6b52d5ffb78ae78 ("rcutorture: Start rcu_torture_writer() after rcu_torture_reader()")
> https://github.com/paulmckrcu/linux dev.2025.05.05a
>
> in testcase: rcutorture
> version:
> with following parameters:
>
> runtime: 300s
> test: default
> torture_type: trivial
Huh. This is the trivial RCU implementation that is not used in the
Linux kernel (aside from rcutorture testing it), but verifies that my
slideware/textbook implementation actually works.
So you didn't manage to break the Linux kernel, just some of my
presentations. ;-)
Still, this clearly needs to be fixed.
> config: i386-randconfig-061-20250510
> compiler: clang-20
> test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G
>
> (please refer to attached dmesg/kmsg for entire log/backtrace)
>
>
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <oliver.sang@...el.com>
> | Closes: https://lore.kernel.org/oe-lkp/202505131651.af6e81d7-lkp@intel.com
>
>
> The kernel config and materials to reproduce are available at:
> https://download.01.org/0day-ci/archive/20250513/202505131651.af6e81d7-lkp@intel.com
>
>
> [ 232.971337][ T965] trivial-torture: rtc: ef358cc0 ver: 9677 tfle: 0 rta: 9677 rtaf: 0 rtf: 9668 rtmbe: 0 rtmbkf: 0/0 rtbe: 0 rtbke: 0 rtbf: 0 rtb: 0 nt: 3782 onoff: 0/0:0/0 -1,0:-1,0 0:0 (HZ=300) barrier: 0/0:0 read-exits: 64 nocb-toggles: 0:0 gpwraps: 0
> [ 232.974503][ T965] trivial-torture: !!!
> [ 232.974595][ T965] ------------[ cut here ]------------
> [ 232.976982][ T965] WARNING: CPU: 0 PID: 965 at kernel/rcu/rcutorture.c:2730 rcu_torture_stats_print+0x8e4/0x8f0 [rcutorture]
And this is a too-short grace period...
> [ 232.980999][ T965] Modules linked in: rcutorture torture
> [ 232.982356][ T965] CPU: 0 UID: 0 PID: 965 Comm: rcu_torture_sta Tainted: G W T 6.15.0-rc1-00059-g54d0803f632b #1 PREEMPT(full) 5f9cb9cacb9aba8a18caee0ed4d4cf4452094bc2
> [ 232.990730][ T965] Tainted: [W]=WARN, [T]=RANDSTRUCT
> [ 232.992782][ T965] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> [ 232.995869][ T965] EIP: rcu_torture_stats_print+0x8e4/0x8f0 [rcutorture]
> [ 232.997526][ T965] Code: ff ff 0f 0b 83 3d 88 8f 35 ef 00 0f 84 b0 fb ff ff 0f 0b 83 3d 8c 8f 35 ef 00 0f 84 ae fb ff ff 0f 0b 84 db 0f 84 ac fb ff ff <0f> 0b e9 a5 fb ff ff 00 00 00 00 00 55 89 e5 53 57 56 83 ec 14 e8
> [ 233.002674][ T965] EAX: 00000004 EBX: 00000001 ECX: 00000000 EDX: 00000000
> [ 233.004477][ T965] ESI: 00000000 EDI: 00000000 EBP: 47efbf58 ESP: 47efbedc
> [ 233.006060][ T965] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 EFLAGS: 00010202
> [ 233.007496][ T965] CR0: 80050033 CR2: 353667f8 CR3: 7c473000 CR4: 000406d0
> [ 233.009173][ T965] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> [ 233.010612][ T965] DR6: fffe0ff0 DR7: 00000400
> [ 233.011678][ T965] Call Trace:
> [ 233.012511][ T965] ? rcu_torture_stats+0x24/0x70 [rcutorture 7eef68a8ad9c4bc219a4bda0dc180602dd9a9416]
> [ 233.014416][ T965] ? kthread+0x1af/0x200
> [ 233.016388][ T965] ? rcu_nocb_toggle+0x1c0/0x1c0 [rcutorture 7eef68a8ad9c4bc219a4bda0dc180602dd9a9416]
> [ 233.018427][ T965] ? schedule_tail+0x79/0xf0
> [ 233.019297][ T965] ? kthread_blkcg+0x30/0x30
> [ 233.020404][ T965] ? kthread_blkcg+0x30/0x30
> [ 233.021230][ T965] ? ret_from_fork+0x2c/0x40
> [ 233.022315][ T965] ? ret_from_fork_asm+0x12/0x20
> [ 233.023169][ T965] ? entry_INT80_32+0x10d/0x10d
> [ 233.024178][ T965] irq event stamp: 495
> [ 233.024991][ T965] hardirqs last enabled at (509): [<4f981d9b>] __console_unlock+0x5b/0x70
> [ 233.026606][ T965] hardirqs last disabled at (520): [<4f981d82>] __console_unlock+0x42/0x70
> [ 233.028125][ T965] softirqs last enabled at (282): [<51ba356a>] __do_softirq+0xa/0xe
> [ 233.029924][ T965] softirqs last disabled at (267): [<51ba356a>] __do_softirq+0xa/0xe
> [ 233.031571][ T965] ---[ end trace 0000000000000000 ]---
> [ 233.033193][ T965] Reader Pipe: 23875253 3963 1 0 0 0 0 0 0 0 0
... as further indicated by the "1" after the "3963". This means that
there was one too-short trivial-RCU grace period in not quite four
minutes of testing.
> [ 233.034030][ T965] trivial-torture: Reader Batch: 23879217 0 0 0 0 0 0 0 0 0 0
> [ 233.035198][ T965] trivial-torture: Free-Block Circulation: 9676 9676 9675 9674 9673 9672 9671 9670 9669 9668 0
>
> ...
>
> [ 472.316419][ T2339] trivial-torture:--- End of test: FAILURE: nreaders=1 nfakewriters=4 stat_interval=60 verbose=1 test_no_idle_hz=1 shuffle_interval=3 stutter=5 irqreader=1 fqs_duration=0 fqs_holdoff=0 fqs_stutter=3 test_boost=1/0 test_boost_interval=7 test_boost_duration=4 test_boost_holdoff=0 shutdown_secs=0 stall_cpu=0 stall_cpu_holdoff=10 stall_cpu_irqsoff=0 stall_cpu_block=0 stall_cpu_repeat=0 n_barrier_cbs=0 onoff_interval=0 onoff_holdoff=0 read_exit_delay=13 read_exit_burst=16 reader_flavor=1 nocbs_nthreads=0 nocbs_toggle=1000 test_nmis=0 preempt_duration=0 preempt_interval=1000 n_up_down=32
And this is one possible reason why: "shuffle_interval=3".
The way that trivial RCU works is to schedule itself on each online CPU
in turn in this function:
static void synchronize_rcu_trivial(void)
{
int cpu;
for_each_online_cpu(cpu) {
torture_sched_setaffinity(current->pid, cpumask_of(cpu), true);
WARN_ON_ONCE(raw_smp_processor_id() != cpu);
}
}
If torture_shuffle_tasks() moves this writer kthread just after the above
torture_sched_setaffinity() completes, then synchronize_rcu_trivial()
might miss its intended CPU, thus failing to wait for RCU readers on
that CPU. This can in turn result in a too-short grace period.
Except that I would expect the WARN_ON_ONCE() to trigger in that scenario.
I will play with this a bit. I don't want to force-disable shuffle
in the torture_type=trivial case because it is a useful way of testing
rcutorture itself. But perhaps I can make the complaint more explicit.
Thanx, Paul
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