Re: [PATCH v2 1/4] sched/task: Add the put_task_struct_atomic_safe function

[luca abeni]

On Wed, 22 Feb 2023 22:00:34 +0100
luca abeni <luca.abeni@xxxxxxxxxxxxxxx> wrote:

> On Wed, 22 Feb 2023 15:42:37 -0300
> Wander Lairson Costa <wander@xxxxxxxxxx> wrote:
> [...]
> > > I triggered this "BUG: Invalid wait context" with a 5.15.76
> > > kernel, without PREEMPT_RT. I can reproduce it easily on a
> > > KVM-based VM; if more information or tests are needed, let me
> > > know. 
> > 
> > Does it happen in linux-6.1 or linux-6.2?  
> 
> I only tried with 5.15.76... I am going to test 6.2 and I'll let you
> know ASAP.

For various reasons it took more time than expected, but I managed to
reproduce the bug with 6.2... Here are the relevant kernel messages:

[ 1246.556100] =============================
[ 1246.559104] [ BUG: Invalid wait context ]
[ 1246.562270] 6.2.0 #4 Not tainted
[ 1246.564854] -----------------------------
[ 1246.567260] swapper/3/0 is trying to lock:
[ 1246.568665] ffff8c2c7ebb2c10 (&c->lock){..-.}-{3:3}, at: put_cpu_partial+0x24/0x1c0
[ 1246.571325] other info that might help us debug this:
[ 1246.573045] context-{2:2}
[ 1246.574166] no locks held by swapper/3/0.
[ 1246.575434] stack backtrace:
[ 1246.576207] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 6.2.0 #4
[ 1246.578184] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
[ 1246.580815] Call Trace:
[ 1246.581723]  <IRQ>
[ 1246.582570]  dump_stack_lvl+0x49/0x61
[ 1246.583860]  __lock_acquire.cold+0xc8/0x31c
[ 1246.584923]  ? __lock_acquire+0x3be/0x1df0
[ 1246.585915]  lock_acquire+0xce/0x2f0
[ 1246.586819]  ? put_cpu_partial+0x24/0x1c0
[ 1246.588177]  ? lock_is_held_type+0xdb/0x130
[ 1246.589519]  put_cpu_partial+0x5b/0x1c0
[ 1246.590996]  ? put_cpu_partial+0x24/0x1c0
[ 1246.592212]  inactive_task_timer+0x263/0x4c0
[ 1246.593509]  ? __pfx_inactive_task_timer+0x10/0x10
[ 1246.594953]  __hrtimer_run_queues+0x1bf/0x470
[ 1246.596297]  hrtimer_interrupt+0x117/0x250
[ 1246.597528]  __sysvec_apic_timer_interrupt+0x99/0x270
[ 1246.599015]  sysvec_apic_timer_interrupt+0x8d/0xc0
[ 1246.600416]  </IRQ>
[ 1246.601170]  <TASK>
[ 1246.601918]  asm_sysvec_apic_timer_interrupt+0x1a/0x20
[ 1246.603377] RIP: 0010:default_idle+0xf/0x20
[ 1246.604640] Code: f6 5d 41 5c e9 72 4a 6e ff cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 03 52 2a 00 fb f4 <c3> cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90
[ 1246.609718] RSP: 0018:ffffa1a2c009bed0 EFLAGS: 00000202
[ 1246.611259] RAX: ffffffffa4961a60 RBX: ffff8c2c4126b000 RCX: 0000000000000000
[ 1246.613230] RDX: 0000000000000000 RSI: ffffffffa510271b RDI: ffffffffa50d5b15
[ 1246.615266] RBP: 0000000000000003 R08: 0000000000000001 R09: 0000000000000001
[ 1246.617275] R10: 0000000000000000 R11: ffff8c2c4126b000 R12: ffff8c2c4126b000
[ 1246.619318] R13: ffff8c2c4126b000 R14: 0000000000000000 R15: 0000000000000000
[ 1246.621293]  ? __pfx_default_idle+0x10/0x10
[ 1246.622581]  default_idle_call+0x71/0x220
[ 1246.623790]  do_idle+0x210/0x290
[ 1246.624827]  cpu_startup_entry+0x18/0x20
[ 1246.626016]  start_secondary+0xf1/0x100
[ 1246.627200]  secondary_startup_64_no_verify+0xe0/0xeb
[ 1246.628707]  </TASK>


Let me know if you need more information, or
I should run other tests/experiments.


				Luca