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author | Qian Cai <cai@redhat.com> | 2020-10-28 21:23:34 +0300 |
---|---|---|
committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-11-02 04:54:20 +0300 |
commit | 99f070b62322a4b8c1252952735806d09eb44b68 (patch) | |
tree | 450e1d03728cab55b85575d88c42e2393a11e25b /arch/powerpc | |
parent | fd552e0542b4532483289cce48fdbd27b692984b (diff) | |
download | linux-99f070b62322a4b8c1252952735806d09eb44b68.tar.xz |
powerpc/smp: Call rcu_cpu_starting() earlier
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@redhat.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
[mpe: Add Fixes tag, reword slightly & expand change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201028182334.13466-1-cai@redhat.com
Diffstat (limited to 'arch/powerpc')
-rw-r--r-- | arch/powerpc/kernel/smp.c | 3 |
1 files changed, 2 insertions, 1 deletions
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; |