Re: [PATCH] powerpc/smp: Move rcu_cpu_starting() earlier
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From: Paul E. McKenney <paulmck@kernel.org>
Date: 2020-10-29 02:11:25
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On Wed, Oct 28, 2020 at 02:23:34PM -0400, Qian Cai wrote:
The call to rcu_cpu_starting() in start_secondary() 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_stack+0xec/0x144 (unreliable) lockdep_rcu_suspicious+0x128/0x14c __lock_acquire+0x1060/0x1c60 lock_acquire+0x140/0x5f0 _raw_spin_lock_irqsave+0x64/0xb0 clockevents_register_device+0x74/0x270 register_decrementer_clockevent+0x94/0x110 start_secondary+0x134/0x800 start_secondary_prolog+0x10/0x14 This is avoided by moving the call to rcu_cpu_starting up near the beginning of the start_secondary() function. Note that the raw_smp_processor_id() is required in order to avoid calling into lockdep before RCU has declared the CPU to be watched for readers. Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/ (local) Signed-off-by: Qian Cai <redacted>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
quoted hunk ↗ jump to hunk
--- arch/powerpc/kernel/smp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c index 3c6b9822f978..8c2857cbd960 100644 --- a/arch/powerpc/kernel/smp.c +++ b/arch/powerpc/kernel/smp.c@@ -1393,13 +1393,14 @@ static void add_cpu_to_masks(int cpu) /* Activate a secondary processor. */ void start_secondary(void *unused) { - unsigned int cpu = smp_processor_id(); + unsigned int cpu = raw_smp_processor_id(); mmgrab(&init_mm); current->active_mm = &init_mm; smp_store_cpu_info(cpu); set_dec(tb_ticks_per_jiffy); + rcu_cpu_starting(cpu); preempt_disable(); cpu_callin_map[cpu] = 1;-- 2.28.0