[PATCH] drm/amdgpu: SRIOV flr_work should use down_write

[Skvortsov, Victor]

[AMD Official Use Only]

I wanted to keep the order the same as in amdgpu_device_lock_adev() 
(Set flag then acquire lock) to prevent any weird race conditions.

Thanks,
Victor

-----Original Message-----
From: Liu, Shaoyun <Shaoyun.Liu at amd.com> 
Sent: Thursday, December 9, 2021 1:25 PM
To: Skvortsov, Victor <Victor.Skvortsov at amd.com>; amd-gfx at lists.freedesktop.org
Cc: Skvortsov, Victor <Victor.Skvortsov at amd.com>
Subject: RE: [PATCH] drm/amdgpu: SRIOV flr_work should use down_write

[AMD Official Use Only]

I think it's a good catch for reset_sem, any reason to change the  adev->in_gpu_reset ?  

Regards
Shaoyun.liu

-----Original Message-----
From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of Victor Skvortsov
Sent: Thursday, December 9, 2021 12:02 PM
To: amd-gfx at lists.freedesktop.org
Cc: Skvortsov, Victor <Victor.Skvortsov at amd.com>
Subject: [PATCH] drm/amdgpu: SRIOV flr_work should use down_write

Host initiated VF FLR may fail if someone else is already holding a read_lock. Change from down_write_trylock to down_write to guarantee the reset goes through.

Signed-off-by: Victor Skvortsov <victor.skvortsov at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/mxgpu_ai.c | 5 +++--  drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/mxgpu_ai.c b/drivers/gpu/drm/amd/amdgpu/mxgpu_ai.c
index cd2719bc0139..e4365c97adaa 100644
--- a/drivers/gpu/drm/amd/amdgpu/mxgpu_ai.c
+++ b/drivers/gpu/drm/amd/amdgpu/mxgpu_ai.c
@@ -252,11 +252,12 @@ static void xgpu_ai_mailbox_flr_work(struct work_struct *work)
 	 * otherwise the mailbox msg will be ruined/reseted by
 	 * the VF FLR.
 	 */
-	if (!down_write_trylock(&adev->reset_sem))
+	if (atomic_cmpxchg(&adev->in_gpu_reset, 0, 1) != 0)
 		return;
 
+	down_write(&adev->reset_sem);
+
 	amdgpu_virt_fini_vf2pf_work_item(adev);
-	atomic_set(&adev->in_gpu_reset, 1);
 
 	xgpu_ai_mailbox_trans_msg(adev, IDH_READY_TO_RESET, 0, 0, 0);
 
diff --git a/drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c b/drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c
index 2bc93808469a..1cde70c72e54 100644
--- a/drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c
+++ b/drivers/gpu/drm/amd/amdgpu/mxgpu_nv.c
@@ -281,11 +281,12 @@ static void xgpu_nv_mailbox_flr_work(struct work_struct *work)
 	 * otherwise the mailbox msg will be ruined/reseted by
 	 * the VF FLR.
 	 */
-	if (!down_write_trylock(&adev->reset_sem))
+	if (atomic_cmpxchg(&adev->in_gpu_reset, 0, 1) != 0)
 		return;
 
+	down_write(&adev->reset_sem);
+
 	amdgpu_virt_fini_vf2pf_work_item(adev);
-	atomic_set(&adev->in_gpu_reset, 1);
 
 	xgpu_nv_mailbox_trans_msg(adev, IDH_READY_TO_RESET, 0, 0, 0);
 
--
2.25.1