On 2023-08-11 17:12, Chen, Xiaogang wrote:
I know the original jira ticket. The system got RCU cpu stall, then
kernel enter panic, then no response or ssh. This patch let prange
list update task yield cpu after each range update. It can prevent
task holding mm lock too long.
Calling schedule does not drop the lock. If anything, it causes the lock
to be held longer, because the function takes longer to complete.
Regards,
Felix
mm lock is rw_semophore, not RCU mechanism. Can you explain how that
can prevent RCU cpu stall in this case?
Regards
Xiaogang
On 8/11/2023 2:11 PM, James Zhu wrote:
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update_list could be big in list_for_each_entry(prange, &update_list,
update_list),
mmap_read_lock(mm) is kept hold all the time, adding schedule() can
remove
RCU stall on CPU for this case.
RIP: 0010:svm_range_cpu_invalidate_pagetables+0x317/0x610 [amdgpu]
Code: 00 00 00 bf 00 02 00 00 48 81 c2 90 00 00 00 e8 1f 6a b9 e0 65
48 8b 14 25 00 bd 01 00 8b 42 2c 48 8b 3c 24 80 e4 f7 0b 43 d8 <89>
42 2c e8 51 dd 2d e1 48 8b 7b 38 e8 98 29 b7 e0 48 83 c4 30 b8
RSP: 0018:ffffc9000ffd7b10 EFLAGS: 00000206
RAX: 0000000000000100 RBX: ffff88c493968d80 RCX: ffff88d1a6469b18
RDX: ffff88e18ef1ec80 RSI: ffffc9000ffd7be0 RDI: ffff88c493968d38
RBP: 000000000003062e R08: 000000003042f000 R09: 000000003062efff
R10: 0000000000001000 R11: ffff88c1ad255000 R12: 000000000003042f
R13: ffff88c493968c00 R14: ffffc9000ffd7be0 R15: ffff88c493968c00
__mmu_notifier_invalidate_range_start+0x132/0x1d0
? amdgpu_vm_bo_update+0x3fd/0x520 [amdgpu]
migrate_vma_setup+0x6c7/0x8f0
? kfd_smi_event_migration_start+0x5f/0x80 [amdgpu]
svm_migrate_ram_to_vram+0x14e/0x580 [amdgpu]
svm_range_set_attr+0xe34/0x11a0 [amdgpu]
kfd_ioctl+0x271/0x4e0 [amdgpu]
? kfd_ioctl_set_xnack_mode+0xd0/0xd0 [amdgpu]
__x64_sys_ioctl+0x92/0xd0
Signed-off-by: James Zhu <James.Zhu@xxxxxxx>
---
drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index 113fd11aa96e..9f2d48ade7fa 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -3573,6 +3573,7 @@ svm_range_set_attr(struct kfd_process *p,
struct mm_struct *mm,
r = svm_range_trigger_migration(mm, prange, &migrated);
if (r)
goto out_unlock_range;
+ schedule();
if (migrated && (!p->xnack_enabled ||
(prange->flags &
KFD_IOCTL_SVM_FLAG_GPU_ALWAYS_MAPPED)) &&
--
2.34.1
