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    Subject[PATCH AUTOSEL 4.19 15/21] s390/smp: move rcu_cpu_starting() earlier
    Date
    From: Qian Cai <cai@redhat.com>

    [ Upstream commit de5d9dae150ca1c1b5c7676711a9ca139d1a8dec ]

    The call to rcu_cpu_starting() in smp_init_secondary() is not early
    enough in the CPU-hotplug onlining process, which results in lockdep
    splats as follows:

    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:
    show_stack+0x158/0x1f0
    dump_stack+0x1f2/0x238
    __lock_acquire+0x2640/0x4dd0
    lock_acquire+0x3a8/0xd08
    _raw_spin_lock_irqsave+0xc0/0xf0
    clockevents_register_device+0xa8/0x528
    init_cpu_timer+0x33e/0x468
    smp_init_secondary+0x11a/0x328
    smp_start_secondary+0x82/0x88

    This is avoided by moving the call to rcu_cpu_starting up near the
    beginning of the smp_init_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.

    Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
    Signed-off-by: Qian Cai <cai@redhat.com>
    Acked-by: Paul E. McKenney <paulmck@kernel.org>
    Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/s390/kernel/smp.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
    index 8e31dfd85de32..888f247c9261a 100644
    --- a/arch/s390/kernel/smp.c
    +++ b/arch/s390/kernel/smp.c
    @@ -831,7 +831,7 @@ void __init smp_detect_cpus(void)
    */
    static void smp_start_secondary(void *cpuvoid)
    {
    - int cpu = smp_processor_id();
    + int cpu = raw_smp_processor_id();

    S390_lowcore.last_update_clock = get_tod_clock();
    S390_lowcore.restart_stack = (unsigned long) restart_stack;
    @@ -844,6 +844,7 @@ static void smp_start_secondary(void *cpuvoid)
    set_cpu_flag(CIF_ASCE_PRIMARY);
    set_cpu_flag(CIF_ASCE_SECONDARY);
    cpu_init();
    + rcu_cpu_starting(cpu);
    preempt_disable();
    init_cpu_timer();
    vtime_init();
    --
    2.27.0
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