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
