Re: [PATCH] drm/amdgpu: Make the submission path memory reclaim safe

[Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>]

On 13/11/2024 14:26, Christian König wrote:
> Am 13.11.24 um 14:48 schrieb Tvrtko Ursulin:
> > From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
> >
> > As commit 746ae46c1113 ("drm/sched: Mark scheduler work queues with 
> > WQ_MEM_RECLAIM")
> > points out, ever since
> > a6149f039369 ("drm/sched: Convert drm scheduler to use a work queue 
> > rather than kthread"),
> > any workqueue flushing done from the job submission path must only
> > involve memory reclaim safe workqueues to be safe against reclaim
> > deadlocks.
> >
> > This is also pointed out by workqueue sanity checks:
> >
> >   [ ] workqueue: WQ_MEM_RECLAIM sdma0:drm_sched_run_job_work 
> > [gpu_sched] is flushing !WQ_MEM_RECLAIM 
> > events:amdgpu_device_delay_enable_gfx_off [amdgpu]
> > ...
> >   [ ] Workqueue: sdma0 drm_sched_run_job_work [gpu_sched]
> > ...
> >   [ ] Call Trace:
> >   [ ]  <TASK>
> > ...
> >   [ ]  ? check_flush_dependency+0xf5/0x110
> > ...
> >   [ ]  cancel_delayed_work_sync+0x6e/0x80
> >   [ ]  amdgpu_gfx_off_ctrl+0xab/0x140 [amdgpu]
> >   [ ]  amdgpu_ring_alloc+0x40/0x50 [amdgpu]
> >   [ ]  amdgpu_ib_schedule+0xf4/0x810 [amdgpu]
> >   [ ]  ? drm_sched_run_job_work+0x22c/0x430 [gpu_sched]
> >   [ ]  amdgpu_job_run+0xaa/0x1f0 [amdgpu]
> >   [ ]  drm_sched_run_job_work+0x257/0x430 [gpu_sched]
> >   [ ]  process_one_work+0x217/0x720
> > ...
> >   [ ]  </TASK>
> >
> > Fix this by creating a memory reclaim safe driver workqueue and make the
> > submission path use it.
>
> Oh well, that is a really good catch! I wasn't aware the workqueues 
> could be blocked by memory reclaim as well.

Only credit I can take is for the habit that I often run with many 
kernel debugging aids enabled.

> Do we have system wide workqueues for that? It seems a bit overkill that 
> amdgpu has to allocate one on his own.

I wondered the same but did not find any. Only ones I am aware of are 
system_wq&co created in workqueue_init_early().

Regards,

Tvrtko

> Apart from that looks good to me.
>
> Regards,
> Christian.
>
> > Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
> > References: 746ae46c1113 ("drm/sched: Mark scheduler work queues with 
> > WQ_MEM_RECLAIM")
> > Fixes: a6149f039369 ("drm/sched: Convert drm scheduler to use a work 
> > queue rather than kthread")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
> > Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
> > Cc: Philipp Stanner <pstanner@xxxxxxxxxx>
> > Cc: Alex Deucher <alexander.deucher@xxxxxxx>
> > Cc: Christian König <christian.koenig@xxxxxxx>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu.h     |  2 ++
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 25 +++++++++++++++++++++++++
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c |  5 +++--
> >   3 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > index 7645e498faa4..a6aad687537e 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
> > @@ -268,6 +268,8 @@ extern int amdgpu_agp;
> >   extern int amdgpu_wbrf;
> > +extern struct workqueue_struct *amdgpu_reclaim_wq;
> > +
> >   #define AMDGPU_VM_MAX_NUM_CTX            4096
> >   #define AMDGPU_SG_THRESHOLD            (256*1024*1024)
> >   #define AMDGPU_WAIT_IDLE_TIMEOUT_IN_MS            3000
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > index 38686203bea6..f5b7172e8042 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
> > @@ -255,6 +255,8 @@ struct amdgpu_watchdog_timer amdgpu_watchdog_timer 
> > = {
> >       .period = 0x0, /* default to 0x0 (timeout disable) */
> >   };
> > +struct workqueue_struct *amdgpu_reclaim_wq;
> > +
> >   /**
> >    * DOC: vramlimit (int)
> >    * Restrict the total amount of VRAM in MiB for testing.  The 
> > default is 0 (Use full VRAM).
> > @@ -2971,6 +2973,21 @@ static struct pci_driver amdgpu_kms_pci_driver = {
> >       .dev_groups = amdgpu_sysfs_groups,
> >   };
> > +static int amdgpu_wq_init(void)
> > +{
> > +    amdgpu_reclaim_wq =
> > +        alloc_workqueue("amdgpu-reclaim", WQ_MEM_RECLAIM, 0);
> > +    if (!amdgpu_reclaim_wq)
> > +        return -ENOMEM;
> > +
> > +    return 0;
> > +}
> > +
> > +static void amdgpu_wq_fini(void)
> > +{
> > +    destroy_workqueue(amdgpu_reclaim_wq);
> > +}
> > +
> >   static int __init amdgpu_init(void)
> >   {
> >       int r;
> > @@ -2978,6 +2995,10 @@ static int __init amdgpu_init(void)
> >       if (drm_firmware_drivers_only())
> >           return -EINVAL;
> > +    r = amdgpu_wq_init();
> > +    if (r)
> > +        goto error_wq;
> > +
> >       r = amdgpu_sync_init();
> >       if (r)
> >           goto error_sync;
> > @@ -3006,6 +3027,9 @@ static int __init amdgpu_init(void)
> >       amdgpu_sync_fini();
> >   error_sync:
> > +    amdgpu_wq_fini();
> > +
> > +error_wq:
> >       return r;
> >   }
> > @@ -3017,6 +3041,7 @@ static void __exit amdgpu_exit(void)
> >       amdgpu_acpi_release();
> >       amdgpu_sync_fini();
> >       amdgpu_fence_slab_fini();
> > +    amdgpu_wq_fini();
> >       mmu_notifier_synchronize();
> >       amdgpu_xcp_drv_release();
> >   }
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c 
> > b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > index 2f3f09dfb1fd..f8fd71d9382f 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gfx.c
> > @@ -790,8 +790,9 @@ void amdgpu_gfx_off_ctrl(struct amdgpu_device 
> > *adev, bool enable)
> >                           AMD_IP_BLOCK_TYPE_GFX, true))
> >                       adev->gfx.gfx_off_state = true;
> >               } else {
> > -                schedule_delayed_work(&adev->gfx.gfx_off_delay_work,
> > -                          delay);
> > +                queue_delayed_work(amdgpu_reclaim_wq,
> > +                           &adev->gfx.gfx_off_delay_work,
> > +                           delay);
> >               }
> >           }
> >       } else {