Qian Cai reported a bug when PROVE_RCU_LIST=y, and read on /proc/lockdep triggered a warning: [26405.676199][ T3548] DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled) ... [26406.402408][ T3548] Call Trace: [26406.416739][ T3548] lock_is_held_type+0x5d/0x150 [26406.438262][ T3548] ? rcu_lockdep_current_cpu_online+0x64/0x80 [26406.466463][ T3548] rcu_read_lock_any_held+0xac/0x100 [26406.490105][ T3548] ? rcu_read_lock_held+0xc0/0xc0 [26406.513258][ T3548] ? __slab_free+0x421/0x540 [26406.535012][ T3548] ? kasan_kmalloc+0x9/0x10 [26406.555901][ T3548] ? __kmalloc_node+0x1d7/0x320 [26406.578668][ T3548] ? kvmalloc_node+0x6f/0x80 [26406.599872][ T3548] __bfs+0x28a/0x3c0 [26406.617075][ T3548] ? class_equal+0x30/0x30 [26406.637524][ T3548] 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@xxxxxx> Signed-off-by: Boqun Feng <boqun.feng@xxxxxxxxx> --- kernel/locking/lockdep.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 32406ef0d6a2..5142a6b11bf5 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; -- 2.25.1
