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Date: Fri, 13 Mar 2020 11:21:07 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
"Joel Fernandes (Google)" <joel@...lfernandes.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
Qian Cai <cai@....pw>, Ingo Molnar <mingo@...hat.com>,
Will Deacon <will@...nel.org>
Subject: Re: [PATCH] locking/lockdep: Avoid recursion in
lockdep_count_{for,back}ward_deps()
On Thu, Mar 12, 2020 at 11:12:55PM +0800, Boqun Feng wrote:
> 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.
This also had me look at __bfs(), while there is a WARN in there, it
doesn't really assert all the expectations.
This lead to the below patch.
---
Subject: locking/lockdep: Rework lockdep_lock
From: Peter Zijlstra <peterz@...radead.org>
Date: Fri Mar 13 11:09:49 CET 2020
A few sites want to assert we own the graph_lock/lockdep_lock, provide
a more conventional lock interface for it with a number of trivial
debug checks.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
kernel/locking/lockdep.c | 89 +++++++++++++++++++++++++----------------------
1 file changed, 48 insertions(+), 41 deletions(-)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -84,12 +84,39 @@ module_param(lock_stat, int, 0644);
* to use a raw spinlock - we really dont want the spinlock
* code to recurse back into the lockdep code...
*/
-static arch_spinlock_t lockdep_lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
+static arch_spinlock_t __lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
+static struct task_struct *__owner;
+
+static inline void lockdep_lock(void)
+{
+ DEBUG_LOCKS_WARN_ON(!irqs_disabled());
+
+ arch_spin_lock(&__lock);
+ __owner = current;
+ current->lockdep_recursion++;
+}
+
+static inline void lockdep_unlock(void)
+{
+ if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current))
+ return;
+
+ current->lockdep_recursion--;
+ __owner = NULL;
+ arch_spin_unlock(&__lock);
+}
+
+static inline bool lockdep_assert_locked(void)
+{
+ return DEBUG_LOCKS_WARN_ON(__owner != current);
+}
+
static struct task_struct *lockdep_selftest_task_struct;
+
static int graph_lock(void)
{
- arch_spin_lock(&lockdep_lock);
+ lockdep_lock();
/*
* Make sure that if another CPU detected a bug while
* walking the graph we dont change it (while the other
@@ -97,27 +124,15 @@ static int graph_lock(void)
* dropped already)
*/
if (!debug_locks) {
- arch_spin_unlock(&lockdep_lock);
+ lockdep_unlock();
return 0;
}
- /* prevent any recursions within lockdep from causing deadlocks */
- current->lockdep_recursion++;
return 1;
}
-static inline int graph_unlock(void)
+static inline void graph_unlock(void)
{
- if (debug_locks && !arch_spin_is_locked(&lockdep_lock)) {
- /*
- * The lockdep graph lock isn't locked while we expect it to
- * be, we're confused now, bye!
- */
- return DEBUG_LOCKS_WARN_ON(1);
- }
-
- current->lockdep_recursion--;
- arch_spin_unlock(&lockdep_lock);
- return 0;
+ lockdep_unlock();
}
/*
@@ -128,7 +143,7 @@ static inline int debug_locks_off_graph_
{
int ret = debug_locks_off();
- arch_spin_unlock(&lockdep_lock);
+ lockdep_unlock();
return ret;
}
@@ -1475,6 +1490,8 @@ static int __bfs(struct lock_list *sourc
struct circular_queue *cq = &lock_cq;
int ret = 1;
+ lockdep_assert_locked();
+
if (match(source_entry, data)) {
*target_entry = source_entry;
ret = 0;
@@ -1497,8 +1514,6 @@ static int __bfs(struct lock_list *sourc
head = get_dep_list(lock, offset);
- DEBUG_LOCKS_WARN_ON(!irqs_disabled());
-
list_for_each_entry_rcu(entry, head, entry) {
if (!lock_accessed(entry)) {
unsigned int cq_depth;
@@ -1725,11 +1740,9 @@ unsigned long lockdep_count_forward_deps
this.class = class;
raw_local_irq_save(flags);
- current->lockdep_recursion++;
- arch_spin_lock(&lockdep_lock);
+ lockdep_lock();
ret = __lockdep_count_forward_deps(&this);
- arch_spin_unlock(&lockdep_lock);
- current->lockdep_recursion--;
+ lockdep_unlock();
raw_local_irq_restore(flags);
return ret;
@@ -1754,11 +1767,9 @@ unsigned long lockdep_count_backward_dep
this.class = class;
raw_local_irq_save(flags);
- current->lockdep_recursion++;
- arch_spin_lock(&lockdep_lock);
+ lockdep_lock();
ret = __lockdep_count_backward_deps(&this);
- arch_spin_unlock(&lockdep_lock);
- current->lockdep_recursion--;
+ lockdep_unlock();
raw_local_irq_restore(flags);
return ret;
@@ -2813,7 +2824,7 @@ static inline int add_chain_cache(struct
* disabled to make this an IRQ-safe lock.. for recursion reasons
* lockdep won't complain about its own locking errors.
*/
- if (DEBUG_LOCKS_WARN_ON(!irqs_disabled()))
+ if (lockdep_assert_locked())
return 0;
chain = alloc_lock_chain();
@@ -4968,8 +4979,7 @@ static void free_zapped_rcu(struct rcu_h
return;
raw_local_irq_save(flags);
- arch_spin_lock(&lockdep_lock);
- current->lockdep_recursion++;
+ lockdep_lock();
/* closed head */
pf = delayed_free.pf + (delayed_free.index ^ 1);
@@ -4981,8 +4991,7 @@ static void free_zapped_rcu(struct rcu_h
*/
call_rcu_zapped(delayed_free.pf + delayed_free.index);
- current->lockdep_recursion--;
- arch_spin_unlock(&lockdep_lock);
+ lockdep_unlock();
raw_local_irq_restore(flags);
}
@@ -5027,13 +5036,11 @@ static void lockdep_free_key_range_reg(v
init_data_structures_once();
raw_local_irq_save(flags);
- arch_spin_lock(&lockdep_lock);
- current->lockdep_recursion++;
+ lockdep_lock();
pf = get_pending_free();
__lockdep_free_key_range(pf, start, size);
call_rcu_zapped(pf);
- current->lockdep_recursion--;
- arch_spin_unlock(&lockdep_lock);
+ lockdep_unlock();
raw_local_irq_restore(flags);
/*
@@ -5055,10 +5062,10 @@ static void lockdep_free_key_range_imm(v
init_data_structures_once();
raw_local_irq_save(flags);
- arch_spin_lock(&lockdep_lock);
+ lockdep_lock();
__lockdep_free_key_range(pf, start, size);
__free_zapped_classes(pf);
- arch_spin_unlock(&lockdep_lock);
+ lockdep_unlock();
raw_local_irq_restore(flags);
}
@@ -5154,10 +5161,10 @@ static void lockdep_reset_lock_imm(struc
unsigned long flags;
raw_local_irq_save(flags);
- arch_spin_lock(&lockdep_lock);
+ lockdep_lock();
__lockdep_reset_lock(pf, lock);
__free_zapped_classes(pf);
- arch_spin_unlock(&lockdep_lock);
+ lockdep_unlock();
raw_local_irq_restore(flags);
}
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