Messages in this thread Patch in this message | | | Subject | Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier | From | Qian Cai <> | Date | Thu, 29 Oct 2020 09:17:35 -0400 |
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On Thu, 2020-10-29 at 09:10 +0000, Will Deacon wrote: > On Wed, Oct 28, 2020 at 02:26:14PM -0400, Qian Cai wrote: > > The call to rcu_cpu_starting() in secondary_start_kernel() is not early > > enough in the CPU-hotplug onlining process, which results in lockdep > > splats as follows: > > > > WARNING: suspicious RCU usage > > ----------------------------- > > kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!! > > > > other info that might help us debug this: > > > > RCU used illegally from offline CPU! > > rcu_scheduler_active = 1, debug_locks = 1 > > no locks held by swapper/1/0. > > > > Call trace: > > dump_backtrace+0x0/0x3c8 > > show_stack+0x14/0x60 > > dump_stack+0x14c/0x1c4 > > lockdep_rcu_suspicious+0x134/0x14c > > __lock_acquire+0x1c30/0x2600 > > lock_acquire+0x274/0xc48 > > _raw_spin_lock+0xc8/0x140 > > vprintk_emit+0x90/0x3d0 > > vprintk_default+0x34/0x40 > > vprintk_func+0x378/0x590 > > printk+0xa8/0xd4 > > __cpuinfo_store_cpu+0x71c/0x868 > > cpuinfo_store_cpu+0x2c/0xc8 > > secondary_start_kernel+0x244/0x318 > > > > This is avoided by moving the call to rcu_cpu_starting up near the > > beginning of the secondary_start_kernel() function. > > Hmm, it's not really a move though -- we'll end up calling this thing twice > afaict. It would be better to make sure we've called notify_cpu_starting() > early enough. Can we do that instead?
Paul mentioned that it is fine to call rcu_cpu_starting() multiple times, and Peter mentioned that CPU bringup is complicated. Thus, I thought about doing something safe here.
I tested a bit of patch below which seems fine, but I can't tell for sure if it is safe. Any suggestion?
--- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -224,6 +224,7 @@ asmlinkage notrace void secondary_start_kernel(void) preempt_disable(); trace_hardirqs_off(); + notify_cpu_starting(cpu); /* * If the system has established the capabilities, make sure @@ -244,7 +245,6 @@ asmlinkage notrace void secondary_start_kernel(void) /* * Enable GIC and timers. */ - notify_cpu_starting(cpu); ipi_setup(cpu);
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