Re: [RFC][PATCH v2 19/31] timers: net: Use del_timer_shutdown() before freeing timer

On 10/27/22 14:07, Steven Rostedt wrote:
> On Thu, 27 Oct 2022 16:34:53 -0400
> Steven Rostedt <[email protected]> wrote:
> 
>> What about del_timer_try_shutdown(), that if it removes the timer, it sets
>> the function to NULL (making it equivalent to a successful shutdown),
>> otherwise it does nothing. Allowing the the timer to be rearmed.
>>
>> I think this would work in this case.
> 
> Guenter,
> 
> Can you apply this patch on top of the series, and see if it makes the
> warning go away?
> 

That patch not only helps, it also fixes the crash seen with openrisc.
For that crash, I was able to collect some useful data; see the log below.

Thanks,
Guenter

---
WARNING: CPU: 0 PID: 7 at lib/debugobjects.c:502 debug_print_object+0xc0/0xe8
ODEBUG: free active (active state 0) object type: timer_list hint: rcu_lock_map+0x0/0x14
Modules linked in:
CPU: 0 PID: 7 Comm: ksoftirqd/0 Not tainted 6.1.0-rc2-00145-g2c4e85e9ac93 #1
Call trace:
[<048ecc8e>] dump_stack_lvl+0x44/0x80
[<c6a7029c>] dump_stack+0x1c/0x2c
[<b225e4eb>] __warn+0xdc/0x118
[<1070b766>] ? debug_print_object+0xc0/0xe8
[<57923a76>] warn_slowpath_fmt+0x78/0x90
[<1070b766>] debug_print_object+0xc0/0xe8
[<b3abbcb0>] __debug_check_no_obj_freed+0x230/0x2b8
[<508d9b5a>] ? delayed_put_task_struct+0x0/0x84
[<30f5a2a0>] ? _s_kernel_ro+0x0/0x200
[<403ab082>] debug_check_no_obj_freed+0x30/0x40
[<82702c56>] free_pcp_prepare+0xc4/0x2b0
[<508d9b5a>] ? delayed_put_task_struct+0x0/0x84
[<7798b190>] free_unref_page+0x44/0x210
[<d73717e5>] __free_pages+0x108/0x124
[<a32de4eb>] slob_free_pages+0x9c/0xac
[<bd51c171>] slob_free+0x40c/0x62c
[<a2d26e0e>] ? thread_stack_free_rcu+0x0/0x44
[<24b2df6c>] ? rcu_process_callbacks+0x114/0x224
[<24b2df6c>] ? rcu_process_callbacks+0x114/0x224
[<7794ec75>] ? rcu_process_callbacks+0xdc/0x224
[<7794ec75>] ? rcu_process_callbacks+0xdc/0x224
[<d76fe88f>] kmem_cache_free+0x64/0xa0
[<46d25dac>] free_task+0x7c/0xe0
[<2df25813>] __put_task_struct+0xe8/0x194
[<64f9675b>] delayed_put_task_struct+0x58/0x84
[<8755437e>] rcu_process_callbacks+0xf0/0x224
[<24b2df6c>] ? rcu_process_callbacks+0x114/0x224
[<020db442>] ? rcu_process_callbacks+0x178/0x224
[<87626af4>] __do_softirq+0x11c/0x2f8
[<c3f89a50>] ? smpboot_thread_fn+0x4c/0x304
[<c3f89a50>] ? smpboot_thread_fn+0x4c/0x304
[<021b0175>] ? smpboot_thread_fn+0x188/0x304
[<f2e79ebd>] ? smpboot_thread_fn+0x158/0x304
[<966be0e6>] run_ksoftirqd+0x4c/0x80
[<4bf65f60>] smpboot_thread_fn+0x180/0x304
[<3f914d93>] ? _raw_spin_unlock_irqrestore+0x50/0x84
[<bef37779>] ? __kthread_parkme+0x60/0xdc
[<b0798e10>] ? smpboot_thread_fn+0x0/0x304
[<c463cd92>] kthread+0x11c/0x144
[<3eaef0b7>] ? kthread+0x0/0x144
[<ef2f6228>] ret_from_fork+0x1c/0x84
---[ end trace 0000000000000000 ]---
Unable to handle kernel access
  at virtual address 0xbd6ed6a4

Oops#: 0000
CPU #: 0
    PC: c0056c78    SR: 00008679    SP: c1027c24
GPR00: 00000000 GPR01: c1027c24 GPR02: c1027c78 GPR03: 00008279
GPR04: 00000000 GPR05: 00000000 GPR06: 00000000 GPR07: 00000001
GPR08: 00000000 GPR09: c0056c64 GPR10: c1026000 GPR11: 00000000
GPR12: 00000000 GPR13: 00000001 GPR14: c05c0000 GPR15: 00000000
GPR16: 00000001 GPR17: bd6ed6a4 GPR18: ff4517b0 GPR19: fd145f00
GPR20: 00000000 GPR21: 00000000 GPR22: 00000000 GPR23: c0760000
GPR24: c10232a0 GPR25: 00000003 GPR26: 00000000 GPR27: 00000000
GPR28: c1a00458 GPR29: 00000000 GPR30: c0790000 GPR31: 00000000
   RES: 00000000 oGPR11: ffffffff
Process ksoftirqd/0 (pid: 7, stackpage=c10232a0)

Stack:
Call trace:
[<6ce5cfad>] __lock_acquire.constprop.0+0xa8/0x914
[<4bc14e12>] ? __del_timer_sync+0x0/0x128
[<da915c87>] lock_acquire.part.0.isra.0+0xd4/0x1ac
[<4bc14e12>] ? __del_timer_sync+0x0/0x128
[<9b341df3>] lock_acquire+0x2c/0x44
[<233b5cbc>] __del_timer_sync+0x64/0x128
[<4bc14e12>] ? __del_timer_sync+0x0/0x128
[<05cd2741>] timer_fixup_free+0x34/0x5c
[<3fa496ad>] __debug_check_no_obj_freed+0x250/0x2b8
[<508d9b5a>] ? delayed_put_task_struct+0x0/0x84
[<30f5a2a0>] ? _s_kernel_ro+0x0/0x200
[<403ab082>] debug_check_no_obj_freed+0x30/0x40
[<82702c56>] free_pcp_prepare+0xc4/0x2b0
[<508d9b5a>] ? delayed_put_task_struct+0x0/0x84
[<7798b190>] free_unref_page+0x44/0x210
[<d73717e5>] __free_pages+0x108/0x124
[<a32de4eb>] slob_free_pages+0x9c/0xac
[<bd51c171>] slob_free+0x40c/0x62c
[<a2d26e0e>] ? thread_stack_free_rcu+0x0/0x44
[<24b2df6c>] ? rcu_process_callbacks+0x114/0x224
[<24b2df6c>] ? rcu_process_callbacks+0x114/0x224
[<7794ec75>] ? rcu_process_callbacks+0xdc/0x224
[<7794ec75>] ? rcu_process_callbacks+0xdc/0x224
[<d76fe88f>] kmem_cache_free+0x64/0xa0
[<46d25dac>] free_task+0x7c/0xe0
[<2df25813>] __put_task_struct+0xe8/0x194
[<64f9675b>] delayed_put_task_struct+0x58/0x84
[<8755437e>] rcu_process_callbacks+0xf0/0x224
[<24b2df6c>] ? rcu_process_callbacks+0x114/0x224
[<020db442>] ? rcu_process_callbacks+0x178/0x224
[<87626af4>] __do_softirq+0x11c/0x2f8
[<c3f89a50>] ? smpboot_thread_fn+0x4c/0x304
[<c3f89a50>] ? smpboot_thread_fn+0x4c/0x304
[<021b0175>] ? smpboot_thread_fn+0x188/0x304
[<f2e79ebd>] ? smpboot_thread_fn+0x158/0x304
[<966be0e6>] run_ksoftirqd+0x4c/0x80
[<4bf65f60>] smpboot_thread_fn+0x180/0x304
[<3f914d93>] ? _raw_spin_unlock_irqrestore+0x50/0x84
[<bef37779>] ? __kthread_parkme+0x60/0xdc
[<b0798e10>] ? smpboot_thread_fn+0x0/0x304
[<c463cd92>] kthread+0x11c/0x144
[<3eaef0b7>] ? kthread+0x0/0x144
[<ef2f6228>] ret_from_fork+0x1c/0x84