There is a deadlock scenario between lockdep and rcu when
rcu nocb feature is enabled, just as following call stack:
rcuop/x
-000|queued_spin_lock_slowpath(lock = 0xFFFFFF817F2A8A80, val = ?)
-001|queued_spin_lock(inline) // try to hold nocb_gp_lock
-001|do_raw_spin_lock(lock = 0xFFFFFF817F2A8A80)
-002|__raw_spin_lock_irqsave(inline)
-002|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F2A8A80)
-003|wake_nocb_gp_defer(inline)
-003|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F30B680)
-004|__call_rcu_common(inline)
-004|call_rcu(head = 0xFFFFFFC082EECC28, func = ?)
-005|call_rcu_zapped(inline)
-005|free_zapped_rcu(ch = ?)// hold graph lock
-006|rcu_do_batch(rdp = 0xFFFFFF817F245680)
-007|nocb_cb_wait(inline)
-007|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F245680)
-008|kthread(_create = 0xFFFFFF80803122C0)
-009|ret_from_fork(asm)
rcuop/y
-000|queued_spin_lock_slowpath(lock = 0xFFFFFFC08291BBC8, val = 0)
-001|queued_spin_lock()
-001|lockdep_lock()
-001|graph_lock() // try to hold graph lock
-002|lookup_chain_cache_add()
-002|validate_chain()
-003|lock_acquire
-004|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F211D80)
-005|lock_timer_base(inline)
-006|mod_timer(inline)
-006|wake_nocb_gp_defer(inline)// hold nocb_gp_lock
-006|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F2A8680)
-007|__call_rcu_common(inline)
-007|call_rcu(head = 0xFFFFFFC0822E0B58, func = ?)
-008|call_rcu_hurry(inline)
-008|rcu_sync_call(inline)
-008|rcu_sync_func(rhp = 0xFFFFFFC0822E0B58)
-009|rcu_do_batch(rdp = 0xFFFFFF817F266680)
-010|nocb_cb_wait(inline)
-010|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F266680)
-011|kthread(_create = 0xFFFFFF8080363740)
-012|ret_from_fork(asm)
rcuop/x and rcuop/y are rcu nocb threads with the same nocb gp thread.
This patch release the graph lock before lockdep call_rcu.
Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
Cc: <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Carlos Llamas <[email protected]>
Cc: Bart Van Assche <[email protected]>
Signed-off-by: Zhiguo Niu <[email protected]>
Signed-off-by: Xuewen Yan <[email protected]>
Reviewed-by: Boqun Feng <[email protected]>
Reviewed-by: Waiman Long <[email protected]>
Reviewed-by: Carlos Llamas <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
---
changes of v4: add Reviewed-by info from reviewers.
changes of v3: correct code comments and add Cc tag.
changes of v2: update patch according to Boqun's suggestions.
---
---
kernel/locking/lockdep.c | 48 ++++++++++++++++++++++++++++++++----------------
1 file changed, 32 insertions(+), 16 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 151bd3d..3468d82 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -6184,25 +6184,27 @@ static struct pending_free *get_pending_free(void)
static void free_zapped_rcu(struct rcu_head *cb);
/*
- * Schedule an RCU callback if no RCU callback is pending. Must be called with
- * the graph lock held.
- */
-static void call_rcu_zapped(struct pending_free *pf)
+* See if we need to queue an RCU callback, must called with
+* the lockdep lock held, returns false if either we don't have
+* any pending free or the callback is already scheduled.
+* Otherwise, a call_rcu() must follow this function call.
+*/
+static bool prepare_call_rcu_zapped(struct pending_free *pf)
{
WARN_ON_ONCE(inside_selftest());
if (list_empty(&pf->zapped))
- return;
+ return false;
if (delayed_free.scheduled)
- return;
+ return false;
delayed_free.scheduled = true;
WARN_ON_ONCE(delayed_free.pf + delayed_free.index != pf);
delayed_free.index ^= 1;
- call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
+ return true;
}
/* The caller must hold the graph lock. May be called from RCU context. */
@@ -6228,6 +6230,7 @@ static void free_zapped_rcu(struct rcu_head *ch)
{
struct pending_free *pf;
unsigned long flags;
+ bool need_callback;
if (WARN_ON_ONCE(ch != &delayed_free.rcu_head))
return;
@@ -6239,14 +6242,18 @@ static void free_zapped_rcu(struct rcu_head *ch)
pf = delayed_free.pf + (delayed_free.index ^ 1);
__free_zapped_classes(pf);
delayed_free.scheduled = false;
+ need_callback =
+ prepare_call_rcu_zapped(delayed_free.pf + delayed_free.index);
+ lockdep_unlock();
+ raw_local_irq_restore(flags);
/*
- * If there's anything on the open list, close and start a new callback.
- */
- call_rcu_zapped(delayed_free.pf + delayed_free.index);
+ * If there's pending free and its callback has not been scheduled,
+ * queue an RCU callback.
+ */
+ if (need_callback)
+ call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
- lockdep_unlock();
- raw_local_irq_restore(flags);
}
/*
@@ -6286,6 +6293,7 @@ static void lockdep_free_key_range_reg(void *start, unsigned long size)
{
struct pending_free *pf;
unsigned long flags;
+ bool need_callback;
init_data_structures_once();
@@ -6293,10 +6301,11 @@ static void lockdep_free_key_range_reg(void *start, unsigned long size)
lockdep_lock();
pf = get_pending_free();
__lockdep_free_key_range(pf, start, size);
- call_rcu_zapped(pf);
+ need_callback = prepare_call_rcu_zapped(pf);
lockdep_unlock();
raw_local_irq_restore(flags);
-
+ if (need_callback)
+ call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
/*
* Wait for any possible iterators from look_up_lock_class() to pass
* before continuing to free the memory they refer to.
@@ -6390,6 +6399,7 @@ static void lockdep_reset_lock_reg(struct lockdep_map *lock)
struct pending_free *pf;
unsigned long flags;
int locked;
+ bool need_callback = false;
raw_local_irq_save(flags);
locked = graph_lock();
@@ -6398,11 +6408,13 @@ static void lockdep_reset_lock_reg(struct lockdep_map *lock)
pf = get_pending_free();
__lockdep_reset_lock(pf, lock);
- call_rcu_zapped(pf);
+ need_callback = prepare_call_rcu_zapped(pf);
graph_unlock();
out_irq:
raw_local_irq_restore(flags);
+ if (need_callback)
+ call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
}
/*
@@ -6446,6 +6458,7 @@ void lockdep_unregister_key(struct lock_class_key *key)
struct pending_free *pf;
unsigned long flags;
bool found = false;
+ bool need_callback = false;
might_sleep();
@@ -6466,11 +6479,14 @@ void lockdep_unregister_key(struct lock_class_key *key)
if (found) {
pf = get_pending_free();
__lockdep_free_key_range(pf, key, 1);
- call_rcu_zapped(pf);
+ need_callback = prepare_call_rcu_zapped(pf);
}
lockdep_unlock();
raw_local_irq_restore(flags);
+ if (need_callback)
+ call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
+
/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
synchronize_rcu();
}
--
1.9.1
On Tue, Feb 06, 2024 at 07:44:55PM +0800, Zhiguo Niu wrote:
> There is a deadlock scenario between lockdep and rcu when
> rcu nocb feature is enabled, just as following call stack:
>
> rcuop/x
> -000|queued_spin_lock_slowpath(lock = 0xFFFFFF817F2A8A80, val = ?)
> -001|queued_spin_lock(inline) // try to hold nocb_gp_lock
> -001|do_raw_spin_lock(lock = 0xFFFFFF817F2A8A80)
> -002|__raw_spin_lock_irqsave(inline)
> -002|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F2A8A80)
> -003|wake_nocb_gp_defer(inline)
> -003|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F30B680)
> -004|__call_rcu_common(inline)
> -004|call_rcu(head = 0xFFFFFFC082EECC28, func = ?)
> -005|call_rcu_zapped(inline)
> -005|free_zapped_rcu(ch = ?)// hold graph lock
> -006|rcu_do_batch(rdp = 0xFFFFFF817F245680)
> -007|nocb_cb_wait(inline)
> -007|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F245680)
> -008|kthread(_create = 0xFFFFFF80803122C0)
> -009|ret_from_fork(asm)
>
> rcuop/y
> -000|queued_spin_lock_slowpath(lock = 0xFFFFFFC08291BBC8, val = 0)
> -001|queued_spin_lock()
> -001|lockdep_lock()
> -001|graph_lock() // try to hold graph lock
> -002|lookup_chain_cache_add()
> -002|validate_chain()
> -003|lock_acquire
> -004|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F211D80)
> -005|lock_timer_base(inline)
> -006|mod_timer(inline)
> -006|wake_nocb_gp_defer(inline)// hold nocb_gp_lock
> -006|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F2A8680)
> -007|__call_rcu_common(inline)
> -007|call_rcu(head = 0xFFFFFFC0822E0B58, func = ?)
> -008|call_rcu_hurry(inline)
> -008|rcu_sync_call(inline)
> -008|rcu_sync_func(rhp = 0xFFFFFFC0822E0B58)
> -009|rcu_do_batch(rdp = 0xFFFFFF817F266680)
> -010|nocb_cb_wait(inline)
> -010|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F266680)
> -011|kthread(_create = 0xFFFFFF8080363740)
> -012|ret_from_fork(asm)
>
> rcuop/x and rcuop/y are rcu nocb threads with the same nocb gp thread.
> This patch release the graph lock before lockdep call_rcu.
>
> Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
> Cc: <[email protected]>
> Cc: Boqun Feng <[email protected]>
> Cc: Waiman Long <[email protected]>
> Cc: Carlos Llamas <[email protected]>
> Cc: Bart Van Assche <[email protected]>
> Signed-off-by: Zhiguo Niu <[email protected]>
> Signed-off-by: Xuewen Yan <[email protected]>
> Reviewed-by: Boqun Feng <[email protected]>
> Reviewed-by: Waiman Long <[email protected]>
> Reviewed-by: Carlos Llamas <[email protected]>
> Reviewed-by: Bart Van Assche <[email protected]>
> ---
This patch should be good to go. Maybe it just slipped through the
cracks. Ingo, will you be taking this?
--
Carlos Llamas
On Tue, Apr 2, 2024 at 11:41 PM Carlos Llamas <[email protected]> wrote:
>
> On Tue, Feb 06, 2024 at 07:44:55PM +0800, Zhiguo Niu wrote:
> > There is a deadlock scenario between lockdep and rcu when
> > rcu nocb feature is enabled, just as following call stack:
> >
> > rcuop/x
> > -000|queued_spin_lock_slowpath(lock = 0xFFFFFF817F2A8A80, val = ?)
> > -001|queued_spin_lock(inline) // try to hold nocb_gp_lock
> > -001|do_raw_spin_lock(lock = 0xFFFFFF817F2A8A80)
> > -002|__raw_spin_lock_irqsave(inline)
> > -002|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F2A8A80)
> > -003|wake_nocb_gp_defer(inline)
> > -003|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F30B680)
> > -004|__call_rcu_common(inline)
> > -004|call_rcu(head = 0xFFFFFFC082EECC28, func = ?)
> > -005|call_rcu_zapped(inline)
> > -005|free_zapped_rcu(ch = ?)// hold graph lock
> > -006|rcu_do_batch(rdp = 0xFFFFFF817F245680)
> > -007|nocb_cb_wait(inline)
> > -007|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F245680)
> > -008|kthread(_create = 0xFFFFFF80803122C0)
> > -009|ret_from_fork(asm)
> >
> > rcuop/y
> > -000|queued_spin_lock_slowpath(lock = 0xFFFFFFC08291BBC8, val = 0)
> > -001|queued_spin_lock()
> > -001|lockdep_lock()
> > -001|graph_lock() // try to hold graph lock
> > -002|lookup_chain_cache_add()
> > -002|validate_chain()
> > -003|lock_acquire
> > -004|_raw_spin_lock_irqsave(lock = 0xFFFFFF817F211D80)
> > -005|lock_timer_base(inline)
> > -006|mod_timer(inline)
> > -006|wake_nocb_gp_defer(inline)// hold nocb_gp_lock
> > -006|__call_rcu_nocb_wake(rdp = 0xFFFFFF817F2A8680)
> > -007|__call_rcu_common(inline)
> > -007|call_rcu(head = 0xFFFFFFC0822E0B58, func = ?)
> > -008|call_rcu_hurry(inline)
> > -008|rcu_sync_call(inline)
> > -008|rcu_sync_func(rhp = 0xFFFFFFC0822E0B58)
> > -009|rcu_do_batch(rdp = 0xFFFFFF817F266680)
> > -010|nocb_cb_wait(inline)
> > -010|rcu_nocb_cb_kthread(arg = 0xFFFFFF817F266680)
> > -011|kthread(_create = 0xFFFFFF8080363740)
> > -012|ret_from_fork(asm)
> >
> > rcuop/x and rcuop/y are rcu nocb threads with the same nocb gp thread.
> > This patch release the graph lock before lockdep call_rcu.
> >
> > Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in use")
> > Cc: <[email protected]>
> > Cc: Boqun Feng <[email protected]>
> > Cc: Waiman Long <[email protected]>
> > Cc: Carlos Llamas <[email protected]>
> > Cc: Bart Van Assche <[email protected]>
> > Signed-off-by: Zhiguo Niu <[email protected]>
> > Signed-off-by: Xuewen Yan <[email protected]>
> > Reviewed-by: Boqun Feng <[email protected]>
> > Reviewed-by: Waiman Long <[email protected]>
> > Reviewed-by: Carlos Llamas <[email protected]>
> > Reviewed-by: Bart Van Assche <[email protected]>
> > ---
>
> This patch should be good to go. Maybe it just slipped through the
> cracks. Ingo, will you be taking this?
Hi Carlos,
Thanks for restoring this mail and now this patch can only be
temporarily included in my code locally when I do related jobs.
and hope someone can help merge it if there are no review suggestions.
>
> --
> Carlos Llamas