Messages in this thread | | | Subject | Re: [PATCH 1/2] cpu/hotplug: Mute hotplug lockdep during init | From | Marc Zyngier <> | Date | Wed, 19 Dec 2018 18:31:49 +0000 |
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On 19/12/2018 18:23, Valentin Schneider wrote: > Since we've had: > > commit cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations") > > we've been getting some lockdep warnings during init, such as on HiKey960: > > [ 0.820495] WARNING: CPU: 4 PID: 0 at kernel/cpu.c:316 lockdep_assert_cpus_held+0x3c/0x48 > [ 0.820498] Modules linked in: > [ 0.820509] CPU: 4 PID: 0 Comm: swapper/4 Tainted: G S 4.20.0-rc5-00051-g4cae42a #34 > [ 0.820511] Hardware name: HiKey960 (DT) > [ 0.820516] pstate: 600001c5 (nZCv dAIF -PAN -UAO) > [ 0.820520] pc : lockdep_assert_cpus_held+0x3c/0x48 > [ 0.820523] lr : lockdep_assert_cpus_held+0x38/0x48 > [ 0.820526] sp : ffff00000a9cbe50 > [ 0.820528] x29: ffff00000a9cbe50 x28: 0000000000000000 > [ 0.820533] x27: 00008000b69e5000 x26: ffff8000bff4cfe0 > [ 0.820537] x25: ffff000008ba69e0 x24: 0000000000000001 > [ 0.820541] x23: ffff000008fce000 x22: ffff000008ba70c8 > [ 0.820545] x21: 0000000000000001 x20: 0000000000000003 > [ 0.820548] x19: ffff00000a35d628 x18: ffffffffffffffff > [ 0.820552] x17: 0000000000000000 x16: 0000000000000000 > [ 0.820556] x15: ffff00000958f848 x14: 455f3052464d4d34 > [ 0.820559] x13: 00000000769dde98 x12: ffff8000bf3f65a8 > [ 0.820564] x11: 0000000000000000 x10: ffff00000958f848 > [ 0.820567] x9 : ffff000009592000 x8 : ffff00000958f848 > [ 0.820571] x7 : ffff00000818ffa0 x6 : 0000000000000000 > [ 0.820574] x5 : 0000000000000000 x4 : 0000000000000001 > [ 0.820578] x3 : 0000000000000000 x2 : 0000000000000001 > [ 0.820582] x1 : 00000000ffffffff x0 : 0000000000000000 > [ 0.820587] Call trace: > [ 0.820591] lockdep_assert_cpus_held+0x3c/0x48 > [ 0.820598] static_key_enable_cpuslocked+0x28/0xd0 > [ 0.820606] arch_timer_check_ool_workaround+0xe8/0x228 > [ 0.820610] arch_timer_starting_cpu+0xe4/0x2d8 > [ 0.820615] cpuhp_invoke_callback+0xe8/0xd08 > [ 0.820619] notify_cpu_starting+0x80/0xb8 > [ 0.820625] secondary_start_kernel+0x118/0x1d0 > > We've also had a similar warning in sched_init_smp() for every > asymmetric system that would enable the sched_asym_cpucapacity static > key, although that was singled out in: > > commit 40fa3780bac2 ("sched/core: Take the hotplug lock in sched_init_smp()") > > Those warnings are actually harmless, since we cannot have hotplug > operations at the time they appear. Instead of starting to sprinkle > useless hotplug lock operations in the init codepaths, mute the > warnings until they start warning about real problems. > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> > --- > FYI Thomas Gleixner suggested using SYSTEM_SCHEDULING instead of > SYSTEM_RUNNING, but that seems to still be too early - sched_init_smp() > (and kernel_init() actually) hasn't completed yet, so we'd still get > those warnings. > --- > kernel/cpu.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/kernel/cpu.c b/kernel/cpu.c > index 91d5c38..34e40ef 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -313,6 +313,15 @@ void cpus_write_unlock(void) > > void lockdep_assert_cpus_held(void) > { > + /* > + * We can't have hotplug operations before userspace starts running, > + * and some init codepaths will knowingly not take the hotplug lock. > + * This is all valid, so mute lockdep until it makes sense to report > + * unheld locks. > + */ > + if (system_state < SYSTEM_RUNNING) > + return; > + > percpu_rwsem_assert_held(&cpu_hotplug_lock); > } > > -- > 2.7.4 >
FWIW: Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Thanks for having kept an eye on it!
M. -- Jazz is not dead. It just smells funny...
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