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    Subject[RFC] lockdep: Put graph lock/unlock under lock_recursion protection
    Date
    A warning was hit when running xfstests/generic/068 in a Hyper-V guest:

    [...] ------------[ cut here ]------------
    [...] DEBUG_LOCKS_WARN_ON(lockdep_hardirqs_enabled())
    [...] WARNING: CPU: 2 PID: 1350 at kernel/locking/lockdep.c:5280 check_flags.part.0+0x165/0x170
    [...] ...
    [...] Workqueue: events pwq_unbound_release_workfn
    [...] RIP: 0010:check_flags.part.0+0x165/0x170
    [...] ...
    [...] Call Trace:
    [...] lock_is_held_type+0x72/0x150
    [...] ? lock_acquire+0x16e/0x4a0
    [...] rcu_read_lock_sched_held+0x3f/0x80
    [...] __send_ipi_one+0x14d/0x1b0
    [...] hv_send_ipi+0x12/0x30
    [...] __pv_queued_spin_unlock_slowpath+0xd1/0x110
    [...] __raw_callee_save___pv_queued_spin_unlock_slowpath+0x11/0x20
    [...] .slowpath+0x9/0xe
    [...] lockdep_unregister_key+0x128/0x180
    [...] pwq_unbound_release_workfn+0xbb/0xf0
    [...] process_one_work+0x227/0x5c0
    [...] worker_thread+0x55/0x3c0
    [...] ? process_one_work+0x5c0/0x5c0
    [...] kthread+0x153/0x170
    [...] ? __kthread_bind_mask+0x60/0x60
    [...] ret_from_fork+0x1f/0x30

    The cause of the problem is we have call chain lockdep_unregister_key()
    -> <irq disabled by raw_local_irq_save()> lockdep_unlock() ->
    arch_spin_unlock() -> __pv_queued_spin_unlock_slowpath() -> pv_kick() ->
    __send_ipi_one() -> trace_hyperv_send_ipi_one().

    Although this particular warning is triggered because Hyper-V has a
    trace point in ipi sending, but in general arch_spin_unlock() may call
    another function having a trace point in it, so put the arch_spin_lock()
    and arch_spin_unlock() after lock_recursion protection to fix this
    problem and avoid similiar problems.

    Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
    Cc: "K. Y. Srinivasan" <kys@microsoft.com>
    Cc: Haiyang Zhang <haiyangz@microsoft.com>
    Cc: Stephen Hemminger <sthemmin@microsoft.com>
    Cc: Wei Liu <wei.liu@kernel.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: x86@kernel.org
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    ---
    kernel/locking/lockdep.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
    index b71ad8d9f1c9..b98e44f88c6a 100644
    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -108,19 +108,21 @@ static inline void lockdep_lock(void)
    {
    DEBUG_LOCKS_WARN_ON(!irqs_disabled());

    + __this_cpu_inc(lockdep_recursion);
    arch_spin_lock(&__lock);
    __owner = current;
    - __this_cpu_inc(lockdep_recursion);
    }

    static inline void lockdep_unlock(void)
    {
    + DEBUG_LOCKS_WARN_ON(!irqs_disabled());
    +
    if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current))
    return;

    - __this_cpu_dec(lockdep_recursion);
    __owner = NULL;
    arch_spin_unlock(&__lock);
    + __this_cpu_dec(lockdep_recursion);
    }

    static inline bool lockdep_assert_locked(void)
    --
    2.29.2
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