On 11/07/2023 15:05, Greg Kroah-Hartman wrote:
> On Tue, Jul 11, 2023 at 03:05:36PM +0800, quanyang.wang@xxxxxxxxxxxxx wrote:
>> From: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
>>
>> For PREEMPT_RT kernel, spinlock_t locks become sleepable. The functions
>> etm_dying_cpu and etm_starting_cpu which call spin_lock/unlock run in
>> an irq-disabled context, this will trigger the following calltrace:
>>
>> BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
>> in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 25, name: migration/1
>> preempt_count: 1, expected: 0
>> RCU nest depth: 0, expected: 0
>> 1 lock held by migration/1/25:
>> #0: 82a7587c (&drvdata->spinlock){....}-{2:2}, at: etm_dying_cpu+0x28/0x54
>> Preemption disabled at:
>> [<801ec760>] cpu_stopper_thread+0x94/0x120
>> CPU: 1 PID: 25 Comm: migration/1 Not tainted 6.1.35-rt10-yocto-preempt-rt #30
>> Hardware name: Xilinx Zynq Platform
>> Stopper: multi_cpu_stop+0x0/0x174 <- __stop_cpus.constprop.0+0x48/0x88
>> unwind_backtrace from show_stack+0x18/0x1c
>> show_stack from dump_stack_lvl+0x58/0x70
>> dump_stack_lvl from __might_resched+0x14c/0x1c0
>> __might_resched from rt_spin_lock+0x4c/0x84
>> rt_spin_lock from etm_dying_cpu+0x28/0x54
>> etm_dying_cpu from cpuhp_invoke_callback+0x140/0x33c
>> cpuhp_invoke_callback from __cpuhp_invoke_callback_range+0xa4/0x104
>> __cpuhp_invoke_callback_range from take_cpu_down+0x7c/0xa8
>> take_cpu_down from multi_cpu_stop+0x15c/0x174
>> multi_cpu_stop from cpu_stopper_thread+0x9c/0x120
>> cpu_stopper_thread from smpboot_thread_fn+0x31c/0x360
>> smpboot_thread_fn from kthread+0x100/0x124
>> kthread from ret_from_fork+0x14/0x2c
>>
>> Convert struct etm_drvdata's spinlock to raw_spinlock to fix it.
>
> wait, why will a raw_spinlock fix this? Why not fix the root problem
> here, that of calling these locks inproperly in irq context?
>
> How is changing to a raw_spinlock going to fix the above splat?
>
> thanks,
>
> greg k-h
>
If it's just etm_starting_cpu() and etm_dying_cpu() as mentioned in the
commit message then can those spinlocks be removed?
Surely there can't be any concurrent access to the per-cpu data when the
hotplug callbacks are called?
James
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
