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    Subject[PATCH 5.4 063/232] locking/lockdep: Avoid recursion in lockdep_count_{for,back}ward_deps()
    Date
    From: Boqun Feng <boqun.feng@gmail.com>

    [ Upstream commit 25016bd7f4caf5fc983bbab7403d08e64cba3004 ]

    Qian Cai reported a bug when PROVE_RCU_LIST=y, and read on /proc/lockdep
    triggered a warning:

    [ ] DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)
    ...
    [ ] Call Trace:
    [ ] lock_is_held_type+0x5d/0x150
    [ ] ? rcu_lockdep_current_cpu_online+0x64/0x80
    [ ] rcu_read_lock_any_held+0xac/0x100
    [ ] ? rcu_read_lock_held+0xc0/0xc0
    [ ] ? __slab_free+0x421/0x540
    [ ] ? kasan_kmalloc+0x9/0x10
    [ ] ? __kmalloc_node+0x1d7/0x320
    [ ] ? kvmalloc_node+0x6f/0x80
    [ ] __bfs+0x28a/0x3c0
    [ ] ? class_equal+0x30/0x30
    [ ] lockdep_count_forward_deps+0x11a/0x1a0

    The warning got triggered because lockdep_count_forward_deps() call
    __bfs() without current->lockdep_recursion being set, as a result
    a lockdep internal function (__bfs()) is checked by lockdep, which is
    unexpected, and the inconsistency between the irq-off state and the
    state traced by lockdep caused the warning.

    Apart from this warning, lockdep internal functions like __bfs() should
    always be protected by current->lockdep_recursion to avoid potential
    deadlocks and data inconsistency, therefore add the
    current->lockdep_recursion on-and-off section to protect __bfs() in both
    lockdep_count_forward_deps() and lockdep_count_backward_deps()

    Reported-by: Qian Cai <cai@lca.pw>
    Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lkml.kernel.org/r/20200312151258.128036-1-boqun.feng@gmail.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/locking/lockdep.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
    index 35d3b6925b1ee..9ab1a965c3b92 100644
    --- a/kernel/locking/lockdep.c
    +++ b/kernel/locking/lockdep.c
    @@ -1719,9 +1719,11 @@ unsigned long lockdep_count_forward_deps(struct lock_class *class)
    this.class = class;

    raw_local_irq_save(flags);
    + current->lockdep_recursion = 1;
    arch_spin_lock(&lockdep_lock);
    ret = __lockdep_count_forward_deps(&this);
    arch_spin_unlock(&lockdep_lock);
    + current->lockdep_recursion = 0;
    raw_local_irq_restore(flags);

    return ret;
    @@ -1746,9 +1748,11 @@ unsigned long lockdep_count_backward_deps(struct lock_class *class)
    this.class = class;

    raw_local_irq_save(flags);
    + current->lockdep_recursion = 1;
    arch_spin_lock(&lockdep_lock);
    ret = __lockdep_count_backward_deps(&this);
    arch_spin_unlock(&lockdep_lock);
    + current->lockdep_recursion = 0;
    raw_local_irq_restore(flags);

    return ret;
    --
    2.20.1


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