| From e191124695dc19780026800e54c2c5d21db070f7 Mon Sep 17 00:00:00 2001 |
| From: Valentin Schneider <valentin.schneider@arm.com> |
| Date: Tue, 23 Oct 2018 14:37:31 +0100 |
| Subject: sched/core: Take the hotplug lock in sched_init_smp() |
| |
| [ Upstream commit 40fa3780bac2b654edf23f6b13f4e2dd550aea10 ] |
| |
| When running on linux-next (8c60c36d0b8c ("Add linux-next specific files |
| for 20181019")) + CONFIG_PROVE_LOCKING=y on a big.LITTLE system (e.g. |
| Juno or HiKey960), we get the following report: |
| |
| [ 0.748225] Call trace: |
| [ 0.750685] lockdep_assert_cpus_held+0x30/0x40 |
| [ 0.755236] static_key_enable_cpuslocked+0x20/0xc8 |
| [ 0.760137] build_sched_domains+0x1034/0x1108 |
| [ 0.764601] sched_init_domains+0x68/0x90 |
| [ 0.768628] sched_init_smp+0x30/0x80 |
| [ 0.772309] kernel_init_freeable+0x278/0x51c |
| [ 0.776685] kernel_init+0x10/0x108 |
| [ 0.780190] ret_from_fork+0x10/0x18 |
| |
| The static_key in question is 'sched_asym_cpucapacity' introduced by |
| commit: |
| |
| df054e8445a4 ("sched/topology: Add static_key for asymmetric CPU capacity optimizations") |
| |
| In this particular case, we enable it because smp_prepare_cpus() will |
| end up fetching the capacity-dmips-mhz entry from the devicetree, |
| so we already have some asymmetry detected when entering sched_init_smp(). |
| |
| This didn't get detected in tip/sched/core because we were missing: |
| |
| commit cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations") |
| |
| Calls to build_sched_domains() post sched_init_smp() will hold the |
| hotplug lock, it just so happens that this very first call is a |
| special case. As stated by a comment in sched_init_smp(), "There's no |
| userspace yet to cause hotplug operations" so this is a harmless |
| warning. |
| |
| However, to both respect the semantics of underlying |
| callees and make lockdep happy, take the hotplug lock in |
| sched_init_smp(). This also satisfies the comment atop |
| sched_init_domains() that says "Callers must hold the hotplug lock". |
| |
| Reported-by: Sudeep Holla <sudeep.holla@arm.com> |
| Tested-by: Sudeep Holla <sudeep.holla@arm.com> |
| Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> |
| Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> |
| Cc: Dietmar.Eggemann@arm.com |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Peter Zijlstra <peterz@infradead.org> |
| Cc: Thomas Gleixner <tglx@linutronix.de> |
| Cc: morten.rasmussen@arm.com |
| Cc: quentin.perret@arm.com |
| Link: http://lkml.kernel.org/r/1540301851-3048-1-git-send-email-valentin.schneider@arm.com |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| kernel/sched/core.c | 5 ++++- |
| 1 file changed, 4 insertions(+), 1 deletion(-) |
| |
| diff --git a/kernel/sched/core.c b/kernel/sched/core.c |
| index ad97f3ba5ec5..35551110d277 100644 |
| --- a/kernel/sched/core.c |
| +++ b/kernel/sched/core.c |
| @@ -5854,11 +5854,14 @@ void __init sched_init_smp(void) |
| /* |
| * There's no userspace yet to cause hotplug operations; hence all the |
| * CPU masks are stable and all blatant races in the below code cannot |
| - * happen. |
| + * happen. The hotplug lock is nevertheless taken to satisfy lockdep, |
| + * but there won't be any contention on it. |
| */ |
| + cpus_read_lock(); |
| mutex_lock(&sched_domains_mutex); |
| sched_init_domains(cpu_active_mask); |
| mutex_unlock(&sched_domains_mutex); |
| + cpus_read_unlock(); |
| |
| /* Move init over to a non-isolated CPU */ |
| if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0) |
| -- |
| 2.17.1 |
| |