[PATCH] drm/amdkfd: drop process ref count when xnack disable

[Kim, Jonathan]

[Public]

I wouldn’t know if it was another bug elsewhere.
From what I was seeing, the leak was coming from !p->xnack_enable on the svm_range_restore_pages call.

If it helps, I saw this on Aldebaran where a shader does some bad memory access on purpose on a debugged ptraced child process.
The vm fault prompt pops up in dmesgs and a stale KFD process appends per run without this fix.
I’m just assuming at this point that the IV retry bit is set but I never confirmed that.

Thanks,

Jon
From: Yang, Philip <Philip.Yang at amd.com>
Sent: Wednesday, September 1, 2021 12:30 PM
To: Kim, Jonathan <Jonathan.Kim at amd.com>; Yang, Philip <Philip.Yang at amd.com>; Sierra Guiza, Alejandro (Alex) <Alex.Sierra at amd.com>; amd-gfx at lists.freedesktop.org
Subject: Re: [PATCH] drm/amdkfd: drop process ref count when xnack disable



On 2021-09-01 9:45 a.m., Kim, Jonathan wrote:

[AMD Official Use Only]

We were seeing process leaks on a couple of machines running certain tests that triggered vm faults on purpose.
I think svm_range_restore_pages gets called unconditionally on vm fault handling (unless the retry interrupt payload bit is supposed to be clear with xnack off)?


yes, with xnack off, sh_mem_config retry should be off, retry bit is supposed to be clear in fault interrupt vector, we should not try to recover vm fault, just report the vm fault back to application and evict user queues. Maybe it is another bug cause p->xnack_enabled and sh_mem_config retry mismatch under specific condition?

Regards,

Philip
Either way, this patch prevents the process leaks we seeing and is also:
Reviewed-by: Jonathan Kim <jonathan.kim at amd.com><mailto:jonathan.kim at amd.com>

Thanks,

Jon


From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org><mailto:amd-gfx-bounces at lists.freedesktop.org> On Behalf Of philip yang
Sent: Wednesday, September 1, 2021 7:30 AM
To: Sierra Guiza, Alejandro (Alex) <Alex.Sierra at amd.com><mailto:Alex.Sierra at amd.com>; amd-gfx at lists.freedesktop.org<mailto:amd-gfx at lists.freedesktop.org>
Subject: Re: [PATCH] drm/amdkfd: drop process ref count when xnack disable

[CAUTION: External Email]


On 2021-08-31 10:41 p.m., Alex Sierra wrote:

During svm restore pages interrupt handler, kfd_process ref count was

never dropped when xnack was disabled. Therefore, the object was never

released.

Good catch, but if xnack is off, we should not get here to recover fault.

The fix looks good to me.

Reviewed-by: Philip Yang <philip.yang at amd.com><mailto:philip.yang at amd.com>



Signed-off-by: Alex Sierra <alex.sierra at amd.com><mailto:alex.sierra at amd.com>

---

 drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 3 ++-

 1 file changed, 2 insertions(+), 1 deletion(-)



diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c

index 8f9b5b53dab5..110c46cd7fac 100644

--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c

+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c

@@ -2484,7 +2484,8 @@ svm_range_restore_pages(struct amdgpu_device *adev, unsigned int pasid,

         }

         if (!p->xnack_enabled) {

                pr_debug("XNACK not enabled for pasid 0x%x\n", pasid);

-               return -EFAULT;

+               r = -EFAULT;

+               goto out;

         }

         svms = &p->svms;


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