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    Subject[PATCH AUTOSEL 5.0 229/262] cpu/hotplug: Mute hotplug lockdep during init
    Date
    From: Valentin Schneider <valentin.schneider@arm.com>

    [ Upstream commit ce48c457b95316b9a01b5aa9d4456ce820df94b4 ]

    Since we've had:

    commit cb538267ea1e ("jump_label/lockdep: Assert we hold the hotplug lock for _cpuslocked() operations")

    we've been getting some lockdep warnings during init, such as on HiKey960:

    [ 0.820495] WARNING: CPU: 4 PID: 0 at kernel/cpu.c:316 lockdep_assert_cpus_held+0x3c/0x48
    [ 0.820498] Modules linked in:
    [ 0.820509] CPU: 4 PID: 0 Comm: swapper/4 Tainted: G S 4.20.0-rc5-00051-g4cae42a #34
    [ 0.820511] Hardware name: HiKey960 (DT)
    [ 0.820516] pstate: 600001c5 (nZCv dAIF -PAN -UAO)
    [ 0.820520] pc : lockdep_assert_cpus_held+0x3c/0x48
    [ 0.820523] lr : lockdep_assert_cpus_held+0x38/0x48
    [ 0.820526] sp : ffff00000a9cbe50
    [ 0.820528] x29: ffff00000a9cbe50 x28: 0000000000000000
    [ 0.820533] x27: 00008000b69e5000 x26: ffff8000bff4cfe0
    [ 0.820537] x25: ffff000008ba69e0 x24: 0000000000000001
    [ 0.820541] x23: ffff000008fce000 x22: ffff000008ba70c8
    [ 0.820545] x21: 0000000000000001 x20: 0000000000000003
    [ 0.820548] x19: ffff00000a35d628 x18: ffffffffffffffff
    [ 0.820552] x17: 0000000000000000 x16: 0000000000000000
    [ 0.820556] x15: ffff00000958f848 x14: 455f3052464d4d34
    [ 0.820559] x13: 00000000769dde98 x12: ffff8000bf3f65a8
    [ 0.820564] x11: 0000000000000000 x10: ffff00000958f848
    [ 0.820567] x9 : ffff000009592000 x8 : ffff00000958f848
    [ 0.820571] x7 : ffff00000818ffa0 x6 : 0000000000000000
    [ 0.820574] x5 : 0000000000000000 x4 : 0000000000000001
    [ 0.820578] x3 : 0000000000000000 x2 : 0000000000000001
    [ 0.820582] x1 : 00000000ffffffff x0 : 0000000000000000
    [ 0.820587] Call trace:
    [ 0.820591] lockdep_assert_cpus_held+0x3c/0x48
    [ 0.820598] static_key_enable_cpuslocked+0x28/0xd0
    [ 0.820606] arch_timer_check_ool_workaround+0xe8/0x228
    [ 0.820610] arch_timer_starting_cpu+0xe4/0x2d8
    [ 0.820615] cpuhp_invoke_callback+0xe8/0xd08
    [ 0.820619] notify_cpu_starting+0x80/0xb8
    [ 0.820625] secondary_start_kernel+0x118/0x1d0

    We've also had a similar warning in sched_init_smp() for every
    asymmetric system that would enable the sched_asym_cpucapacity static
    key, although that was singled out in:

    commit 40fa3780bac2 ("sched/core: Take the hotplug lock in sched_init_smp()")

    Those warnings are actually harmless, since we cannot have hotplug
    operations at the time they appear. Instead of starting to sprinkle
    useless hotplug lock operations in the init codepaths, mute the
    warnings until they start warning about real problems.

    Suggested-by: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: cai@gmx.us
    Cc: daniel.lezcano@linaro.org
    Cc: dietmar.eggemann@arm.com
    Cc: linux-arm-kernel@lists.infradead.org
    Cc: longman@redhat.com
    Cc: marc.zyngier@arm.com
    Cc: mark.rutland@arm.com
    Link: https://lkml.kernel.org/r/1545243796-23224-2-git-send-email-valentin.schneider@arm.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/cpu.c | 9 +++++++++
    1 file changed, 9 insertions(+)

    diff --git a/kernel/cpu.c b/kernel/cpu.c
    index d1c6d152da89..025f419d16f6 100644
    --- a/kernel/cpu.c
    +++ b/kernel/cpu.c
    @@ -313,6 +313,15 @@ void cpus_write_unlock(void)

    void lockdep_assert_cpus_held(void)
    {
    + /*
    + * We can't have hotplug operations before userspace starts running,
    + * and some init codepaths will knowingly not take the hotplug lock.
    + * This is all valid, so mute lockdep until it makes sense to report
    + * unheld locks.
    + */
    + if (system_state < SYSTEM_RUNNING)
    + return;
    +
    percpu_rwsem_assert_held(&cpu_hotplug_lock);
    }

    --
    2.19.1
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