drm/amdkfd: Fix lock dependency warning with srcu

======================================================
WARNING: possible circular locking dependency detected
6.5.0-kfd-yangp #2289 Not tainted
------------------------------------------------------
kworker/0:2/996 is trying to acquire lock:
        (srcu){.+.+}-{0:0}, at: __synchronize_srcu+0x5/0x1a0

but task is already holding lock:
        ((work_completion)(&svms->deferred_list_work)){+.+.}-{0:0}, at:
	process_one_work+0x211/0x560

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 ((work_completion)(&svms->deferred_list_work)){+.+.}-{0:0}:
        __flush_work+0x88/0x4f0
        svm_range_list_lock_and_flush_work+0x3d/0x110 [amdgpu]
        svm_range_set_attr+0xd6/0x14c0 [amdgpu]
        kfd_ioctl+0x1d1/0x630 [amdgpu]
        __x64_sys_ioctl+0x88/0xc0

-> #2 (&info->lock#2){+.+.}-{3:3}:
        __mutex_lock+0x99/0xc70
        amdgpu_amdkfd_gpuvm_restore_process_bos+0x54/0x740 [amdgpu]
        restore_process_helper+0x22/0x80 [amdgpu]
        restore_process_worker+0x2d/0xa0 [amdgpu]
        process_one_work+0x29b/0x560
        worker_thread+0x3d/0x3d0

-> #1 ((work_completion)(&(&process->restore_work)->work)){+.+.}-{0:0}:
        __flush_work+0x88/0x4f0
        __cancel_work_timer+0x12c/0x1c0
        kfd_process_notifier_release_internal+0x37/0x1f0 [amdgpu]
        __mmu_notifier_release+0xad/0x240
        exit_mmap+0x6a/0x3a0
        mmput+0x6a/0x120
        do_exit+0x322/0xb90
        do_group_exit+0x37/0xa0
        __x64_sys_exit_group+0x18/0x20
        do_syscall_64+0x38/0x80

-> #0 (srcu){.+.+}-{0:0}:
        __lock_acquire+0x1521/0x2510
        lock_sync+0x5f/0x90
        __synchronize_srcu+0x4f/0x1a0
        __mmu_notifier_release+0x128/0x240
        exit_mmap+0x6a/0x3a0
        mmput+0x6a/0x120
        svm_range_deferred_list_work+0x19f/0x350 [amdgpu]
        process_one_work+0x29b/0x560
        worker_thread+0x3d/0x3d0

other info that might help us debug this:
Chain exists of:
  srcu --> &info->lock#2 --> (work_completion)(&svms->deferred_list_work)

Possible unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
        lock((work_completion)(&svms->deferred_list_work));
                        lock(&info->lock#2);
			lock((work_completion)(&svms->deferred_list_work));
        sync(srcu);

Signed-off-by: Philip Yang <[email protected]>
Reviewed-by: Felix Kuehling <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

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

@@ -2340,8 +2340,10 @@ static void svm_range_deferred_list_work(struct work_struct *work)
 		mutex_unlock(&svms->lock);
 		mmap_write_unlock(mm);
 
-		/* Pairs with mmget in svm_range_add_list_work */
-		mmput(mm);
+		/* Pairs with mmget in svm_range_add_list_work. If dropping the
+		 * last mm refcount, schedule release work to avoid circular locking
+		 */
+		mmput_async(mm);
 
 		spin_lock(&svms->deferred_list_lock);
 	}