linux-kernel - [PATCH 5.5 075/257] locking/lockdep: Avoid recursion in lockdep_count_{for,back}ward

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Message-Id: <20200416131335.345336402@linuxfoundation.org>
Date:   Thu, 16 Apr 2020 15:22:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Qian Cai <cai@....pw>,
        Boqun Feng <boqun.feng@...il.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.5 075/257] locking/lockdep: Avoid recursion in lockdep_count_{for,back}ward_deps()

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

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 32406ef0d6a2d..5142a6b11bf5b 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