[tip: locking/core] lockdep: Fix lockdep recursion

From: tip-bot2 for Peter Zijlstra
Date: Fri Oct 09 2020 - 03:58:47 EST

The following commit has been merged into the locking/core branch of tip:

Commit-ID: 4d004099a668c41522242aa146a38cc4eb59cb1e
Gitweb: https://git.kernel.org/tip/4d004099a668c41522242aa146a38cc4eb59cb1e
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Fri, 02 Oct 2020 11:04:21 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Fri, 09 Oct 2020 08:53:30 +02:00

lockdep: Fix lockdep recursion

Steve reported that lockdep_assert*irq*(), when nested inside lockdep
itself, will trigger a false-positive.

One example is the stack-trace code, as called from inside lockdep,
triggering tracing, which in turn calls RCU, which then uses
lockdep_assert_irqs_disabled().

Fixes: a21ee6055c30 ("lockdep: Change hardirq{s_enabled,_context} to per-cpu variables")
Reported-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
include/linux/lockdep.h | 13 +++--
kernel/locking/lockdep.c | 99 ++++++++++++++++++++++----------------
2 files changed, 67 insertions(+), 45 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 6a584b3..b1227be 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -534,6 +534,7 @@ do { \

DECLARE_PER_CPU(int, hardirqs_enabled);
DECLARE_PER_CPU(int, hardirq_context);
+DECLARE_PER_CPU(unsigned int, lockdep_recursion);

/*
* The below lockdep_assert_*() macros use raw_cpu_read() to access the above
@@ -543,25 +544,27 @@ DECLARE_PER_CPU(int, hardirq_context);
* read the value from our previous CPU.
*/

+#define __lockdep_enabled (debug_locks && !raw_cpu_read(lockdep_recursion))
+
#define lockdep_assert_irqs_enabled() \
do { \
- WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirqs_enabled)); \
+ WARN_ON_ONCE(__lockdep_enabled && !raw_cpu_read(hardirqs_enabled)); \
} while (0)

#define lockdep_assert_irqs_disabled() \
do { \
- WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled)); \
+ WARN_ON_ONCE(__lockdep_enabled && raw_cpu_read(hardirqs_enabled)); \
} while (0)

#define lockdep_assert_in_irq() \
do { \
- WARN_ON_ONCE(debug_locks && !raw_cpu_read(hardirq_context)); \
+ WARN_ON_ONCE(__lockdep_enabled && !raw_cpu_read(hardirq_context)); \
} while (0)

#define lockdep_assert_preemption_enabled() \
do { \
WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT) && \
- debug_locks && \
+ __lockdep_enabled && \
(preempt_count() != 0 || \
!raw_cpu_read(hardirqs_enabled))); \
} while (0)
@@ -569,7 +572,7 @@ do { \
#define lockdep_assert_preemption_disabled() \
do { \
WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_COUNT) && \
- debug_locks && \
+ __lockdep_enabled && \
(preempt_count() == 0 && \
raw_cpu_read(hardirqs_enabled))); \
} while (0)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index a430fbb..85d15f0 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -76,6 +76,23 @@ module_param(lock_stat, int, 0644);
#define lock_stat 0
#endif

+DEFINE_PER_CPU(unsigned int, lockdep_recursion);
+EXPORT_PER_CPU_SYMBOL_GPL(lockdep_recursion);
+
+static inline bool lockdep_enabled(void)
+{
+ if (!debug_locks)
+ return false;
+
+ if (raw_cpu_read(lockdep_recursion))
+ return false;
+
+ if (current->lockdep_recursion)
+ return false;
+
+ return true;
+}
+
/*
* lockdep_lock: protects the lockdep graph, the hashes and the
* class/list/hash allocators.
@@ -93,7 +110,7 @@ static inline void lockdep_lock(void)

arch_spin_lock(&__lock);
__owner = current;
- current->lockdep_recursion++;
+ __this_cpu_inc(lockdep_recursion);
}

static inline void lockdep_unlock(void)
@@ -101,7 +118,7 @@ static inline void lockdep_unlock(void)
if (debug_locks && DEBUG_LOCKS_WARN_ON(__owner != current))
return;

- current->lockdep_recursion--;
+ __this_cpu_dec(lockdep_recursion);
__owner = NULL;
arch_spin_unlock(&__lock);
}
@@ -393,10 +410,15 @@ void lockdep_init_task(struct task_struct *task)
task->lockdep_recursion = 0;
}

+static __always_inline void lockdep_recursion_inc(void)
+{
+ __this_cpu_inc(lockdep_recursion);
+}
+
static __always_inline void lockdep_recursion_finish(void)
{
- if (WARN_ON_ONCE((--current->lockdep_recursion) & LOCKDEP_RECURSION_MASK))
- current->lockdep_recursion = 0;
+ if (WARN_ON_ONCE(__this_cpu_dec_return(lockdep_recursion)))
+ __this_cpu_write(lockdep_recursion, 0);
}

void lockdep_set_selftest_task(struct task_struct *task)
@@ -3659,7 +3681,7 @@ void lockdep_hardirqs_on_prepare(unsigned long ip)
if (unlikely(in_nmi()))
return;

- if (unlikely(current->lockdep_recursion & LOCKDEP_RECURSION_MASK))
+ if (unlikely(__this_cpu_read(lockdep_recursion)))
return;

if (unlikely(lockdep_hardirqs_enabled())) {
@@ -3695,7 +3717,7 @@ void lockdep_hardirqs_on_prepare(unsigned long ip)

current->hardirq_chain_key = current->curr_chain_key;

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
__trace_hardirqs_on_caller();
lockdep_recursion_finish();
}
@@ -3728,7 +3750,7 @@ void noinstr lockdep_hardirqs_on(unsigned long ip)
goto skip_checks;
}

- if (unlikely(current->lockdep_recursion & LOCKDEP_RECURSION_MASK))
+ if (unlikely(__this_cpu_read(lockdep_recursion)))
return;

if (lockdep_hardirqs_enabled()) {
@@ -3781,7 +3803,7 @@ void noinstr lockdep_hardirqs_off(unsigned long ip)
if (in_nmi()) {
if (!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_NMI))
return;
- } else if (current->lockdep_recursion & LOCKDEP_RECURSION_MASK)
+ } else if (__this_cpu_read(lockdep_recursion))
return;

/*
@@ -3814,7 +3836,7 @@ void lockdep_softirqs_on(unsigned long ip)
{
struct irqtrace_events *trace = &current->irqtrace;

- if (unlikely(!debug_locks || current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

/*
@@ -3829,7 +3851,7 @@ void lockdep_softirqs_on(unsigned long ip)
return;
}

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
/*
* We'll do an OFF -> ON transition:
*/
@@ -3852,7 +3874,7 @@ void lockdep_softirqs_on(unsigned long ip)
*/
void lockdep_softirqs_off(unsigned long ip)
{
- if (unlikely(!debug_locks || current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

/*
@@ -4233,11 +4255,11 @@ void lockdep_init_map_waits(struct lockdep_map *lock, const char *name,
if (subclass) {
unsigned long flags;

- if (DEBUG_LOCKS_WARN_ON(current->lockdep_recursion))
+ if (DEBUG_LOCKS_WARN_ON(!lockdep_enabled()))
return;

raw_local_irq_save(flags);
- current->lockdep_recursion++;
+ lockdep_recursion_inc();
register_lock_class(lock, subclass, 1);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -4920,11 +4942,11 @@ void lock_set_class(struct lockdep_map *lock, const char *name,
{
unsigned long flags;

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

raw_local_irq_save(flags);
- current->lockdep_recursion++;
+ lockdep_recursion_inc();
check_flags(flags);
if (__lock_set_class(lock, name, key, subclass, ip))
check_chain_key(current);
@@ -4937,11 +4959,11 @@ void lock_downgrade(struct lockdep_map *lock, unsigned long ip)
{
unsigned long flags;

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

raw_local_irq_save(flags);
- current->lockdep_recursion++;
+ lockdep_recursion_inc();
check_flags(flags);
if (__lock_downgrade(lock, ip))
check_chain_key(current);
@@ -4979,7 +5001,7 @@ static void verify_lock_unused(struct lockdep_map *lock, struct held_lock *hlock

static bool lockdep_nmi(void)
{
- if (current->lockdep_recursion & LOCKDEP_RECURSION_MASK)
+ if (raw_cpu_read(lockdep_recursion))
return false;

if (!in_nmi())
@@ -5000,7 +5022,10 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,

trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);

- if (unlikely(current->lockdep_recursion)) {
+ if (!debug_locks)
+ return;
+
+ if (unlikely(!lockdep_enabled())) {
/* XXX allow trylock from NMI ?!? */
if (lockdep_nmi() && !trylock) {
struct held_lock hlock;
@@ -5023,7 +5048,7 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
raw_local_irq_save(flags);
check_flags(flags);

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
__lock_acquire(lock, subclass, trylock, read, check,
irqs_disabled_flags(flags), nest_lock, ip, 0, 0);
lockdep_recursion_finish();
@@ -5037,13 +5062,13 @@ void lock_release(struct lockdep_map *lock, unsigned long ip)

trace_lock_release(lock, ip);

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

raw_local_irq_save(flags);
check_flags(flags);

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
if (__lock_release(lock, ip))
check_chain_key(current);
lockdep_recursion_finish();
@@ -5056,13 +5081,13 @@ noinstr int lock_is_held_type(const struct lockdep_map *lock, int read)
unsigned long flags;
int ret = 0;

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return 1; /* avoid false negative lockdep_assert_held() */

raw_local_irq_save(flags);
check_flags(flags);

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
ret = __lock_is_held(lock, read);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -5077,13 +5102,13 @@ struct pin_cookie lock_pin_lock(struct lockdep_map *lock)
struct pin_cookie cookie = NIL_COOKIE;
unsigned long flags;

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return cookie;

raw_local_irq_save(flags);
check_flags(flags);

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
cookie = __lock_pin_lock(lock);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -5096,13 +5121,13 @@ void lock_repin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
{
unsigned long flags;

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

raw_local_irq_save(flags);
check_flags(flags);

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
__lock_repin_lock(lock, cookie);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -5113,13 +5138,13 @@ void lock_unpin_lock(struct lockdep_map *lock, struct pin_cookie cookie)
{
unsigned long flags;

- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lockdep_enabled()))
return;

raw_local_irq_save(flags);
check_flags(flags);

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
__lock_unpin_lock(lock, cookie);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -5249,15 +5274,12 @@ void lock_contended(struct lockdep_map *lock, unsigned long ip)

trace_lock_acquired(lock, ip);

- if (unlikely(!lock_stat || !debug_locks))
- return;
-
- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lock_stat || !lockdep_enabled()))
return;

raw_local_irq_save(flags);
check_flags(flags);
- current->lockdep_recursion++;
+ lockdep_recursion_inc();
__lock_contended(lock, ip);
lockdep_recursion_finish();
raw_local_irq_restore(flags);
@@ -5270,15 +5292,12 @@ void lock_acquired(struct lockdep_map *lock, unsigned long ip)

trace_lock_contended(lock, ip);

- if (unlikely(!lock_stat || !debug_locks))
- return;
-
- if (unlikely(current->lockdep_recursion))
+ if (unlikely(!lock_stat || !lockdep_enabled()))
return;

raw_local_irq_save(flags);
check_flags(flags);
- current->lockdep_recursion++;
+ lockdep_recursion_inc();
__lock_acquired(lock, ip);
lockdep_recursion_finish();
raw_local_irq_restore(flags);