From: Qian Cai <cai@xxxxxxxxxx>
commit 99f070b62322a4b8c1252952735806d09eb44b68 upstream.
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 (with CONFIG_PROVE_RCU_LIST=y):
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 adding a call to rcu_cpu_starting() 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.
It's safe to call rcu_cpu_starting() in the arch code as well as later
in generic code, as explained by Paul:
It uses a per-CPU variable so that RCU pays attention only to the
first call to rcu_cpu_starting() if there is more than one of them.
This is even intentional, due to there being a generic
arch-independent call to rcu_cpu_starting() in
notify_cpu_starting().
So multiple calls to rcu_cpu_starting() are fine by design.
Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion")
Signed-off-by: Qian Cai <cai@xxxxxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
[mpe: Add Fixes tag, reword slightly & expand change log]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20201028182334.13466-1-cai@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kernel/smp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1251,7 +1251,7 @@ static bool shared_caches;
/* Activate a secondary processor. */
void start_secondary(void *unused)
{
- unsigned int cpu = smp_processor_id();
+ unsigned int cpu = raw_smp_processor_id();
struct cpumask *(*sibling_mask)(int) = cpu_sibling_mask;
mmgrab(&init_mm);
