Re: [WARNING] kernel/rcu/tree.c:1058 rcu_irq_enter+0x15/0x20

From: Peter Zijlstra
Date: Fri Oct 02 2020 - 05:04:44 EST

On Wed, Sep 30, 2020 at 03:52:22PM -0400, Steven Rostedt wrote:
> On Wed, 30 Sep 2020 21:22:42 +0200
> Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> > On Wed, Sep 30, 2020 at 03:10:26PM -0400, Steven Rostedt wrote:
> > > On Wed, 30 Sep 2020 20:13:23 +0200
> > > Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > > > diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> > > > > index 6a584b3e5c74..3e5bc1dd71c6 100644
> > > > > --- a/include/linux/lockdep.h
> > > > > +++ b/include/linux/lockdep.h
> > > > > @@ -550,7 +550,8 @@ do { \
> > > > >
> > > > > #define lockdep_assert_irqs_disabled() \
> > > > > do { \
> > > > > - WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled)); \
> > > > > + WARN_ON_ONCE(debug_locks && raw_cpu_read(hardirqs_enabled) && \
> > > > > + likely(!(current->lockdep_recursion & LOCKDEP_RECURSION_MASK)));\
> > > > > } while (0)
> > > >
> > > > Blergh, IIRC there's header hell that way. The sane fix is killing off
> > > > that trace_*_rcuidle() disease.
> > >
> > > Really?
> > >
> > > I could run this through all my other tests to see if that is the case.
> > > That is, to see if it stumbles across header hell.
> >
> > I went through a lot of pain to make that per-cpu to avoid using
> > current. But that might've been driven by
> > lockdep_assert_preemption_disabled(), which is used in seqlock.h which
> > in turn is included all over the place.
> >
> > That said, there's at least two things we can do:
> >
> > - make lockdep_recursion per-cpu too, IIRC we only ever set that when
> > we have IRQs disabled anyway.
> >
> > OR
> >
> > - inspired by the above, as can save/clear - restore hardirqs_enabled
> > when we frob lockdep_recursion.
> >
> > Admittedly, the second is somewhat gross :-)
>
> I think making lockdep_recursion percpu sounds like the best approach.
>
> -- Steve

Bugger, we use current->lockdep_recursion also for lockdep_off(); I
always forget about that thing.

Anyway, something like so then.

---
include/linux/lockdep.h | 13 +++---
kernel/locking/lockdep.c | 101 ++++++++++++++++++++++++++++-------------------
2 files changed, 68 insertions(+), 46 deletions(-)

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 57d642d378c7..1cc982536640 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -559,6 +559,7 @@ 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
@@ -568,25 +569,27 @@ 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)
@@ -594,7 +597,7 @@ 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 454355c033d2..47942557b4fb 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -76,6 +76,22 @@ module_param(lock_stat, int, 0644);
#define lock_stat 0
#endif

+DEFINE_PER_CPU(unsigned int, lockdep_recursion);
+
+static inline bool lockdep_enabled(void)
+{
+ if (!debug_locks)
+ return false;
+
+ if (__this_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 +109,7 @@ 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 +117,7 @@ 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);
}
@@ -408,10 +424,15 @@ 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)
@@ -4012,7 +4033,7 @@ 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())) {
@@ -4048,7 +4069,7 @@ 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();
}
@@ -4081,7 +4102,7 @@ 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()) {
@@ -4134,7 +4155,7 @@ 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;

/*
@@ -4167,7 +4188,7 @@ 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;

/*
@@ -4182,7 +4203,7 @@ void lockdep_softirqs_on(unsigned long ip)
return;
}

- current->lockdep_recursion++;
+ lockdep_recursion_inc();
/*
* We'll do an OFF -> ON transition:
*/
@@ -4205,7 +4226,7 @@ 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;

/*
@@ -4590,11 +4611,11 @@ 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);
@@ -5277,11 +5298,11 @@ 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);
@@ -5294,11 +5315,11 @@ 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);
@@ -5336,7 +5357,7 @@ 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 (__this_cpu_read(lockdep_recursion))
return false;

if (!in_nmi())
@@ -5371,7 +5392,11 @@ 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;
+
+ raw_local_irq_save(flags);
+ if (unlikely(!lockdep_enabled())) {
/* XXX allow trylock from NMI ?!? */
if (lockdep_nmi() && !trylock) {
struct held_lock hlock;
@@ -5388,13 +5413,13 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,

verify_lock_unused(lock, &hlock, subclass);
}
+ raw_local_irq_restore(flags);
return;
}

- 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();
@@ -5408,13 +5433,13 @@ 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();
@@ -5427,13 +5452,13 @@ 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);
@@ -5448,13 +5473,13 @@ 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);
@@ -5467,13 +5492,13 @@ 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);
@@ -5484,13 +5509,13 @@ 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);
@@ -5620,15 +5645,12 @@ 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);
@@ -5641,15 +5663,12 @@ 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);