LinuxLists.cc - [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu

2024-01-17 07:51:12

Subject: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu

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")
Signed-off-by: Zhiguo Niu <[email protected]>
Signed-off-by: Xuewen Yan <[email protected]>
---
changes of v2: update patch according to Boqun's suggestions.
---
---
kernel/locking/lockdep.c | 47 +++++++++++++++++++++++++++++++----------------
1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 151bd3d..ddcaa69 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 +6242,17 @@ 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 anything on the open list, close and start a new callback.
+ */
+ if (need_callback)
+ call_rcu(&delayed_free.rcu_head, free_zapped_rcu);

- lockdep_unlock();
- raw_local_irq_restore(flags);
}

/*
@@ -6286,6 +6292,7 @@ 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 +6300,11 @@ 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 +6398,7 @@ 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 +6407,13 @@ 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 +6457,7 @@ 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 +6478,14 @@ 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

2024-01-17 15:06:33

by Waiman Long

[permalink] [raw]

Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu

On 1/17/24 02:48, 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")
> Signed-off-by: Zhiguo Niu <[email protected]>
> Signed-off-by: Xuewen Yan <[email protected]>
> ---
> changes of v2: update patch according to Boqun's suggestions.
> ---
> ---
> kernel/locking/lockdep.c | 47 +++++++++++++++++++++++++++++++----------------
> 1 file changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 151bd3d..ddcaa69 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 +6242,17 @@ 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 anything on the open list, close and start a new callback.
> + */
> + if (need_callback)
> + call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
>
> - lockdep_unlock();
> - raw_local_irq_restore(flags);
> }
>
> /*
> @@ -6286,6 +6292,7 @@ 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 +6300,11 @@ 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 +6398,7 @@ 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 +6407,13 @@ 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 +6457,7 @@ 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 +6478,14 @@ 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();
> }

LGTM.

Reviewed-by: Waiman Long <[email protected]>

2024-01-17 21:01:21

by Boqun Feng

[permalink] [raw]

Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu

On Wed, Jan 17, 2024 at 03:48:34PM +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")
> Signed-off-by: Zhiguo Niu <[email protected]>
> Signed-off-by: Xuewen Yan <[email protected]>

Reviewed-by: Boqun Feng <[email protected]>

Regards,
Boqun

> ---
> changes of v2: update patch according to Boqun's suggestions.
> ---
> ---
> kernel/locking/lockdep.c | 47 +++++++++++++++++++++++++++++++----------------
> 1 file changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 151bd3d..ddcaa69 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 +6242,17 @@ 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 anything on the open list, close and start a new callback.
> + */
> + if (need_callback)
> + call_rcu(&delayed_free.rcu_head, free_zapped_rcu);
>
> - lockdep_unlock();
> - raw_local_irq_restore(flags);
> }
>
> /*
> @@ -6286,6 +6292,7 @@ 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 +6300,11 @@ 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 +6398,7 @@ 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 +6407,13 @@ 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 +6457,7 @@ 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 +6478,14 @@ 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
>

2024-02-01 17:10:08

by Carlos Llamas

[permalink] [raw]

Dear All,
Thanks for your discussion and suggestions , I update and send patch
version3 according to your comments.
thanks!

On Fri, Feb 2, 2024 at 10:13 AM Bart Van Assche <[email protected]> wrote:
>
> On 2/1/24 13:53, Boqun Feng wrote:
> > Have you checked the change in the patch? Now call_rcu_zapped() has been
> > splitted into two parts: preparing the callback and calling call_rcu(),
> > the preparing part checks and sets the delayed_free.scheduled under
> > graph_lock(), so only one CPU/thread will win and do the actual
> > call_rcu(). And the RCU callback free_zapped_rcu() will unset
> > delayed_free.scheduled, again under graph_lock().
> >
> > If you think it's still possible, could you provide a case where the
> > race may happen?
>
> Yes, I noticed that call_rcu_zapped() has been split but the first time
> I took a look at this patch I wasn't sure that the new code is correct.
> After having taken a second look, the new mechanism for deciding whether
> or not to invoke call_rcu() seems fine to me.
>
> Bart.