Hi Paul,
"Paul E. McKenney" <paulmck@xxxxxxxxxx> writes:
> Nice speedup!
>
> However, I am not convinced that the code shown below is safe.
>
> I believe that you need either a synchronize_rcu() in your free_ipc()
> function or that you need to pass free_ipc() to queue_rcu_work() instead
> of directly schedule_work(). As things are, I would expect you to see
> free_ipc_ns() being invoke too soon on heavily loaded CONFIG_PREEMPT=y
> kernels. Which can be quite a pain to debug!
>
> Or am I missing something?
thanks for the review!
Would being called too soon be a problem? The current version calls
free_ipc_ns() as part of the put_ipc_ns cleanup.
free_ipc() calls immediately synchronize_rcu() through free_ipc_ns():
free_ipc_ns() -> mq_put_mnt() -> kern_unmount() -> synchronize_rcu()
Do you think we should make it more explicit and add a synchronize_rcu()
as part of the free_ipc_ns() function itself?
Regards,
Giuseppe
>
> Thanx, Paul
>
>> Signed-off-by: Giuseppe Scrivano <gscrivan@xxxxxxxxxx>
>> ---
>> include/linux/ipc_namespace.h | 2 ++
>> ipc/namespace.c | 17 +++++++++++++++--
>> 2 files changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
>> index c309f43bde45..a06a78c67f19 100644
>> --- a/include/linux/ipc_namespace.h
>> +++ b/include/linux/ipc_namespace.h
>> @@ -68,6 +68,8 @@ struct ipc_namespace {
>> struct user_namespace *user_ns;
>> struct ucounts *ucounts;
>>
>> + struct llist_node mnt_llist;
>> +
>> struct ns_common ns;
>> } __randomize_layout;
>>
>> diff --git a/ipc/namespace.c b/ipc/namespace.c
>> index b3ca1476ca51..37d27e1b807a 100644
>> --- a/ipc/namespace.c
>> +++ b/ipc/namespace.c
>> @@ -117,6 +117,7 @@ void free_ipcs(struct ipc_namespace *ns, struct ipc_ids *ids,
>>
>> static void free_ipc_ns(struct ipc_namespace *ns)
>> {
>> + mq_put_mnt(ns);
>> sem_exit_ns(ns);
>> msg_exit_ns(ns);
>> shm_exit_ns(ns);
>> @@ -127,6 +128,17 @@ static void free_ipc_ns(struct ipc_namespace *ns)
>> kfree(ns);
>> }
>>
>> +static LLIST_HEAD(free_ipc_list);
>> +static void free_ipc(struct work_struct *unused)
>> +{
>> + struct llist_node *node = llist_del_all(&free_ipc_list);
>> + struct ipc_namespace *n, *t;
>> +
>> + llist_for_each_entry_safe(n, t, node, mnt_llist)
>> + free_ipc_ns(n);
>> +}
>> +static DECLARE_WORK(free_ipc_work, free_ipc);
>> +
>> /*
>> * put_ipc_ns - drop a reference to an ipc namespace.
>> * @ns: the namespace to put
>> @@ -148,8 +160,9 @@ void put_ipc_ns(struct ipc_namespace *ns)
>> if (refcount_dec_and_lock(&ns->count, &mq_lock)) {
>> mq_clear_sbinfo(ns);
>> spin_unlock(&mq_lock);
>> - mq_put_mnt(ns);
>> - free_ipc_ns(ns);
>> +
>> + if (llist_add(&ns->mnt_llist, &free_ipc_list))
>> + schedule_work(&free_ipc_work);
>> }
>> }
>>
>> --
>> 2.24.1
>>
