drm/amdgpu: Replace Mutex with Spinlock for RLCG register access to avoid Priority...

RLCG Register Access is a way for virtual functions to safely access GPU
registers in a virtualized environment., including TLB flushes and
register reads. When multiple threads or VFs try to access the same
registers simultaneously, it can lead to race conditions. By using the
RLCG interface, the driver can serialize access to the registers. This
means that only one thread can access the registers at a time,
preventing conflicts and ensuring that operations are performed
correctly. Additionally, when a low-priority task holds a mutex that a
high-priority task needs, ie., If a thread holding a spinlock tries to
acquire a mutex, it can lead to priority inversion. register access in
amdgpu_virt_rlcg_reg_rw especially in a fast code path is critical.

The call stack shows that the function amdgpu_virt_rlcg_reg_rw is being
called, which attempts to acquire the mutex. This function is invoked
from amdgpu_sriov_wreg, which in turn is called from
gmc_v11_0_flush_gpu_tlb.

The [ BUG: Invalid wait context ] indicates that a thread is trying to
acquire a mutex while it is in a context that does not allow it to sleep
(like holding a spinlock).

Fixes the below:

[  253.013423] =============================
[  253.013434] [ BUG: Invalid wait context ]
[  253.013446] 6.12.0-amdstaging-drm-next-lol-050225 #14 Tainted: G     U     OE
[  253.013464] -----------------------------
[  253.013475] kworker/0:1/10 is trying to lock:
[  253.013487] ffff9f30542e3cf8 (&adev->virt.rlcg_reg_lock){+.+.}-{3:3}, at: amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]
[  253.013815] other info that might help us debug this:
[  253.013827] context-{4:4}
[  253.013835] 3 locks held by kworker/0:1/10:
[  253.013847]  #0: ffff9f3040050f58 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x3f5/0x680
[  253.013877]  #1: ffffb789c008be40 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_one_work+0x1d6/0x680
[  253.013905]  #2: ffff9f3054281838 (&adev->gmc.invalidate_lock){+.+.}-{2:2}, at: gmc_v11_0_flush_gpu_tlb+0x198/0x4f0 [amdgpu]
[  253.014154] stack backtrace:
[  253.014164] CPU: 0 UID: 0 PID: 10 Comm: kworker/0:1 Tainted: G     U     OE      6.12.0-amdstaging-drm-next-lol-050225 #14
[  253.014189] Tainted: [U]=USER, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
[  253.014203] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 11/18/2024
[  253.014224] Workqueue: events work_for_cpu_fn
[  253.014241] Call Trace:
[  253.014250]  <TASK>
[  253.014260]  dump_stack_lvl+0x9b/0xf0
[  253.014275]  dump_stack+0x10/0x20
[  253.014287]  __lock_acquire+0xa47/0x2810
[  253.014303]  ? srso_alias_return_thunk+0x5/0xfbef5
[  253.014321]  lock_acquire+0xd1/0x300
[  253.014333]  ? amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]
[  253.014562]  ? __lock_acquire+0xa6b/0x2810
[  253.014578]  __mutex_lock+0x85/0xe20
[  253.014591]  ? amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]
[  253.014782]  ? sched_clock_noinstr+0x9/0x10
[  253.014795]  ? srso_alias_return_thunk+0x5/0xfbef5
[  253.014808]  ? local_clock_noinstr+0xe/0xc0
[  253.014822]  ? amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]
[  253.015012]  ? srso_alias_return_thunk+0x5/0xfbef5
[  253.015029]  mutex_lock_nested+0x1b/0x30
[  253.015044]  ? mutex_lock_nested+0x1b/0x30
[  253.015057]  amdgpu_virt_rlcg_reg_rw+0xf6/0x330 [amdgpu]
[  253.015249]  amdgpu_sriov_wreg+0xc5/0xd0 [amdgpu]
[  253.015435]  gmc_v11_0_flush_gpu_tlb+0x44b/0x4f0 [amdgpu]
[  253.015667]  gfx_v11_0_hw_init+0x499/0x29c0 [amdgpu]
[  253.015901]  ? __pfx_smu_v13_0_update_pcie_parameters+0x10/0x10 [amdgpu]
[  253.016159]  ? srso_alias_return_thunk+0x5/0xfbef5
[  253.016173]  ? smu_hw_init+0x18d/0x300 [amdgpu]
[  253.016403]  amdgpu_device_init+0x29ad/0x36a0 [amdgpu]
[  253.016614]  amdgpu_driver_load_kms+0x1a/0xc0 [amdgpu]
[  253.017057]  amdgpu_pci_probe+0x1c2/0x660 [amdgpu]
[  253.017493]  local_pci_probe+0x4b/0xb0
[  253.017746]  work_for_cpu_fn+0x1a/0x30
[  253.017995]  process_one_work+0x21e/0x680
[  253.018248]  worker_thread+0x190/0x330
[  253.018500]  ? __pfx_worker_thread+0x10/0x10
[  253.018746]  kthread+0xe7/0x120
[  253.018988]  ? __pfx_kthread+0x10/0x10
[  253.019231]  ret_from_fork+0x3c/0x60
[  253.019468]  ? __pfx_kthread+0x10/0x10
[  253.019701]  ret_from_fork_asm+0x1a/0x30
[  253.019939]  </TASK>

v2: s/spin_trylock/spin_lock_irqsave to be safe (Christian).

Fixes: e864180ee49b ("drm/amdgpu: Add lock around VF RLCG interface")
Cc: lin cao <lin.cao@amd.com>
Cc: Jingwen Chen <Jingwen.Chen2@amd.com>
Cc: Victor Skvortsov <victor.skvortsov@amd.com>
Cc: Zhigang Luo <zhigang.luo@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 1230ab2ba1120cb7afa4df3d3da889dcd2b74396..5aa0b40322911465872665d1d25411442562e0f0 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -4257,7 +4257,6 @@ int amdgpu_device_init(struct amdgpu_device *adev,
        mutex_init(&adev->grbm_idx_mutex);
        mutex_init(&adev->mn_lock);
        mutex_init(&adev->virt.vf_errors.lock);
-       mutex_init(&adev->virt.rlcg_reg_lock);
        hash_init(adev->mn_hash);
        mutex_init(&adev->psp.mutex);
        mutex_init(&adev->notifier_lock);
@@ -4283,6 +4282,7 @@ int amdgpu_device_init(struct amdgpu_device *adev,
        spin_lock_init(&adev->se_cac_idx_lock);
        spin_lock_init(&adev->audio_endpt_idx_lock);
        spin_lock_init(&adev->mm_stats.lock);
+       spin_lock_init(&adev->virt.rlcg_reg_lock);
        spin_lock_init(&adev->wb.lock);
 
        INIT_LIST_HEAD(&adev->reset_list);

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
index 2056efaf157d5a656b7af0b7d524b7eac1fc4f60..e6f0152e5b08720e4775d82ffd5b694370ee74b2 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.c
@@ -1017,6 +1017,7 @@ u32 amdgpu_virt_rlcg_reg_rw(struct amdgpu_device *adev, u32 offset, u32 v, u32 f
        void *scratch_reg2;
        void *scratch_reg3;
        void *spare_int;
+       unsigned long flags;
 
        if (!adev->gfx.rlc.rlcg_reg_access_supported) {
                dev_err(adev->dev,
@@ -1038,7 +1039,7 @@ u32 amdgpu_virt_rlcg_reg_rw(struct amdgpu_device *adev, u32 offset, u32 v, u32 f
        scratch_reg2 = (void __iomem *)adev->rmmio + 4 * reg_access_ctrl->scratch_reg2;
        scratch_reg3 = (void __iomem *)adev->rmmio + 4 * reg_access_ctrl->scratch_reg3;
 
-       mutex_lock(&adev->virt.rlcg_reg_lock);
+       spin_lock_irqsave(&adev->virt.rlcg_reg_lock, flags);
 
        if (reg_access_ctrl->spare_int)
                spare_int = (void __iomem *)adev->rmmio + 4 * reg_access_ctrl->spare_int;
@@ -1097,7 +1098,7 @@ u32 amdgpu_virt_rlcg_reg_rw(struct amdgpu_device *adev, u32 offset, u32 v, u32 f
 
        ret = readl(scratch_reg0);
 
-       mutex_unlock(&adev->virt.rlcg_reg_lock);
+       spin_unlock_irqrestore(&adev->virt.rlcg_reg_lock, flags);
 
        return ret;
 }

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
index 270a032e2d70997a4c8c53f699d9bde0ea4bca0b..0f3ccae5c1ab3bc7777f8e0480abbfe23e8f4644 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
@@ -279,7 +279,8 @@ struct amdgpu_virt {
        /* the ucode id to signal the autoload */
        uint32_t autoload_ucode_id;
 
-       struct mutex rlcg_reg_lock;
+       /* Spinlock to protect access to the RLCG register interface */
+       spinlock_t rlcg_reg_lock;
 
        union amd_sriov_ras_caps ras_en_caps;
        union amd_sriov_ras_caps ras_telemetry_en_caps;