# next BUG: using smp\_processor\_id() in preemptible

- From: Hugh Dickins \<hughd@google.com\>
- Date: 2011-12-05 23:51:54 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2011/12/9467490
- Thread: https://ratatoskr.run/linuxppc-dev/2011/12/9467490/t.md

```text
3.2.0-rc3-next-20111202 with CONFIG_DEBUG_PREEMPT=y gives me lots of

Dec  4 20:03:19 thorn kernel: BUG: using smp_processor_id() in preemptible [00000000] code: startpar/1365
Dec  4 20:03:19 thorn kernel: caller is .arch_local_irq_restore+0x44/0x90
Dec  4 20:03:19 thorn kernel: Call Trace:
Dec  4 20:03:19 thorn kernel: [c0000001b45a7c60] [c000000000011fe8] .show_stack+0x6c/0x16c (unreliable)
Dec  4 20:03:19 thorn kernel: [c0000001b45a7d10] [c00000000024318c] .debug_smp_processor_id+0xe4/0x11c
Dec  4 20:03:19 thorn kernel: [c0000001b45a7da0] [c00000000000e2e8] .arch_local_irq_restore+0x44/0x90
Dec  4 20:03:19 thorn kernel: [c0000001b45a7e30] [c000000000005870] .do_hash_page+0x70/0x74
Dec  4 20:03:21 thorn kernel: debug_smp_processor_id: 21950 callbacks suppressed

from the u64 *next_tb = &__get_cpu_var(decrementers_next_tb)
in decrementer_check_overflow(): I've no idea whether it's safe
just to use get_cpu_var then put_cpu_var there instead,
but no hurry, I can survive with DEBUG_PREEMPT off.

Hugh
```