4.19-stable review patch. If anyone has any objections, please let me know.
------------------
[ 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.ho...@arm.com>
Tested-by: Sudeep Holla <sudeep.ho...@arm.com>
Signed-off-by: Valentin Schneider <valentin.schnei...@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Cc: dietmar.eggem...@arm.com
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: morten.rasmus...@arm.com
Cc: quentin.per...@arm.com
Link:
http://lkml.kernel.org/r/1540301851-3048-1-git-send-email-valentin.schnei...@arm.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Sasha Levin <sas...@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
