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Subject[tip: locking/core] locking/lockdep: Avoid recursion in lockdep_count_{for,back}ward_deps()
The following commit has been merged into the locking/core branch of tip:

Commit-ID: 25016bd7f4caf5fc983bbab7403d08e64cba3004
Gitweb: https://git.kernel.org/tip/25016bd7f4caf5fc983bbab7403d08e64cba3004
Author: Boqun Feng <boqun.feng@gmail.com>
AuthorDate: Thu, 12 Mar 2020 23:12:55 +08:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Fri, 20 Mar 2020 13:06:25 +01:00

locking/lockdep: Avoid recursion in lockdep_count_{for,back}ward_deps()

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
---
kernel/locking/lockdep.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index e55c4ee..2564950 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -1723,9 +1723,11 @@ 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;
@@ -1750,9 +1752,11 @@ 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;
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