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    Subject[PATCH AUTOSEL 5.4 24/24] arm64/smp: Move rcu_cpu_starting() earlier
    Date
    From: Qian Cai <cai@redhat.com>

    [ Upstream commit ce3d31ad3cac765484463b4f5a0b6b1f8f1a963e ]

    The call to rcu_cpu_starting() in secondary_start_kernel() 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:
    dump_backtrace+0x0/0x3c8
    show_stack+0x14/0x60
    dump_stack+0x14c/0x1c4
    lockdep_rcu_suspicious+0x134/0x14c
    __lock_acquire+0x1c30/0x2600
    lock_acquire+0x274/0xc48
    _raw_spin_lock+0xc8/0x140
    vprintk_emit+0x90/0x3d0
    vprintk_default+0x34/0x40
    vprintk_func+0x378/0x590
    printk+0xa8/0xd4
    __cpuinfo_store_cpu+0x71c/0x868
    cpuinfo_store_cpu+0x2c/0xc8
    secondary_start_kernel+0x244/0x318

    This is avoided by moving the call to rcu_cpu_starting up near the
    beginning of the secondary_start_kernel() function.

    Signed-off-by: Qian Cai <cai@redhat.com>
    Acked-by: Paul E. McKenney <paulmck@kernel.org>
    Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
    Link: https://lore.kernel.org/r/20201028182614.13655-1-cai@redhat.com
    Signed-off-by: Will Deacon <will@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/arm64/kernel/smp.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
    index 102dc3e7f2e1d..426409e0d0713 100644
    --- a/arch/arm64/kernel/smp.c
    +++ b/arch/arm64/kernel/smp.c
    @@ -215,6 +215,7 @@ asmlinkage notrace void secondary_start_kernel(void)
    if (system_uses_irq_prio_masking())
    init_gic_priority_masking();

    + rcu_cpu_starting(cpu);
    preempt_disable();
    trace_hardirqs_off();

    --
    2.27.0
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