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;