Quoting Tvrtko Ursulin (2018-10-03 09:05:07)
>
> On 02/10/2018 14:29, Chris Wilson wrote:
> > As the kthread may terminate itself, the parent must hold a task_struct
> > reference for it to call kthread_stop().
> >
> > <4> [498.827675] stack segment: 0000 [#1] PREEMPT SMP PTI
> > <4> [498.827683] CPU: 0 PID: 3872 Comm: drv_selftest Tainted: G U 4.19.0-rc6-CI-CI_DRM_4915+ #1
> > <4> [498.827686] Hardware name: Intel Corporation NUC7CJYH/NUC7JYB, BIOS JYGLKCPX.86A.0027.2018.0125.1347 01/25/2018
> > <4> [498.827695] RIP: 0010:kthread_stop+0x36/0x210
> > <4> [498.827698] Code: 05 df 3d f6 7e 89 c0 48 0f a3 05 95 f8 29 01 0f 82 56 01 00 00 f0 ff 43 20 f6 43 26 20 0f 84 7f 01 00 00 48 8b ab b0 05 00 00 <f0> 80 4d 00 02 48 89 df e8 5d ff ff ff 48 89 df e8 15 c7 00 00 48
> > <4> [498.827701] RSP: 0018:ffffc900003937d0 EFLAGS: 00010202
> > <4> [498.827704] RAX: 0000000000000001 RBX: ffff8802165ece40 RCX: 0000000000000001
> > <4> [498.827707] RDX: 0000000000000000 RSI: 00000000ffffffff RDI: ffffffff82247460
> > <4> [498.827709] RBP: 6b6b6b6b6b6b6b6b R08: 00000000581395cb R09: 0000000000000001
> > <4> [498.827711] R10: 0000000000000000 R11: 0000000000000000 R12: ffffc90000393868
> > <4> [498.827713] R13: ffffc900003937f0 R14: ffff88026c068040 R15: 0000000000001057
> > <4> [498.827716] FS: 00007fc0c464b980(0000) GS:ffff880277e00000(0000) knlGS:0000000000000000
> > <4> [498.827718] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > <4> [498.827720] CR2: 000056178c2feca0 CR3: 000000026983c000 CR4: 0000000000340ef0
> > <4> [498.827723] Call Trace:
> > <4> [498.827824] smoke_crescendo+0x14c/0x1d0 [i915]
> > <4> [498.827837] ? _raw_spin_unlock_irqrestore+0x4c/0x60
> > <4> [498.827898] ? __i915_gem_context_pin_hw_id+0x69/0x5f0 [i915]
> > <4> [498.827902] ? ida_alloc_range+0x1f2/0x3d0
> > <4> [498.827907] ? __mutex_unlock_slowpath+0x46/0x2b0
> > <4> [498.827914] ? rcu_lockdep_current_cpu_online+0x8f/0xd0
> > <4> [498.827979] live_preempt_smoke+0x2c2/0x470 [i915]
> > <4> [498.828047] __i915_subtests+0x5e/0xf0 [i915]
> > <4> [498.828113] __run_selftests+0x10b/0x190 [i915]
> > <4> [498.828175] i915_live_selftests+0x2c/0x60 [i915]
> > <4> [498.828232] i915_pci_probe+0x50/0xa0 [i915]
> > <4> [498.828238] pci_device_probe+0xa1/0x130
> > <4> [498.828244] really_probe+0x25d/0x3c0
> > <4> [498.828249] driver_probe_device+0x10a/0x120
> > <4> [498.828253] __driver_attach+0xdb/0x100
> > <4> [498.828256] ? driver_probe_device+0x120/0x120
> > <4> [498.828259] bus_for_each_dev+0x74/0xc0
> > <4> [498.828264] bus_add_driver+0x15f/0x250
> > <4> [498.828268] ? 0xffffffffa00c3000
> > <4> [498.828271] driver_register+0x56/0xe0
> > <4> [498.828274] ? 0xffffffffa00c3000
> > <4> [498.828278] do_one_initcall+0x58/0x2e0
> > <4> [498.828281] ? rcu_lockdep_current_cpu_online+0x8f/0xd0
> > <4> [498.828285] ? do_init_module+0x1d/0x1ea
> > <4> [498.828289] ? rcu_read_lock_sched_held+0x6f/0x80
> > <4> [498.828293] ? kmem_cache_alloc_trace+0x264/0x290
> > <4> [498.828297] do_init_module+0x56/0x1ea
> > <4> [498.828302] load_module+0x26f5/0x29d0
> > <4> [498.828309] ? vfs_read+0x122/0x140
> > <4> [498.828318] ? __se_sys_finit_module+0xd3/0xf0
> > <4> [498.828321] __se_sys_finit_module+0xd3/0xf0
> > <4> [498.828329] do_syscall_64+0x55/0x190
> > <4> [498.828332] entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > <4> [498.828335] RIP: 0033:0x7fc0c3f16839
> >
> > Fixes: 992d2098ef0b ("drm/i915/selftests: Split preemption smoke test into threads")
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/selftests/intel_lrc.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/selftests/intel_lrc.c b/drivers/gpu/drm/i915/selftests/intel_lrc.c
> > index 9f241d1c72db..94fc0e5c8766 100644
> > --- a/drivers/gpu/drm/i915/selftests/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/selftests/intel_lrc.c
> > @@ -696,6 +696,7 @@ static int smoke_crescendo(struct preempt_smoke *smoke, unsigned int flags)
> > err = PTR_ERR(tsk[id]);
> > break;
> > }
> > + get_task_struct(tsk[id]);
> > }
> >
> > count = 0;
> > @@ -710,6 +711,8 @@ static int smoke_crescendo(struct preempt_smoke *smoke, unsigned int flags)
> > err = status;
> >
> > count += arg[id].count;
> > +
> > + put_task_struct(tsk[id]);
> > }
> >
> > mutex_lock(&smoke->i915->drm.struct_mutex);
> >
>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Ta, fixed even before Martin or Tomi spotted the bug.
-Chris
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