Re: [PATCH 07/12] target/pr: Convert registration check to RCU pointer

Christoph Hellwig
2015-05-13T06:13:44Z

On Tue, May 12, 2015 at 09:25:31AM +0000, Nicholas A. Bellinger wrote:
> From: Nicholas Bellinger <nab@linux-iscsi.org>
>
> This patch converts core_scsi3_pr_seq_non_holder() check for non
> reservation holding registrations to use se_deve->pr_reg as an RCU
> protected pointer.

->pr_reg is only used a boolean flag:

drivers/target/target_core_device.c: rcu_assign_pointer(orig->pr_reg, NULL);
drivers/target/target_core_pr.c: registered = (se_deve->pr_reg
!= NULL);
drivers/target/target_core_pr.c:
rcu_assign_pointer(deve->pr_reg, pr_reg);
drivers/target/target_core_pr.c: * conditional checks for deve->pr_reg
pointer access complete.
drivers/target/target_core_pr.c:
rcu_assign_pointer(deve->pr_reg, pr_reg_tmp);
drivers/target/target_core_pr.c: * conditional checks for
deve->pr_reg pointer access complete.
drivers/target/target_core_pr.c:
rcu_assign_pointer(deve->pr_reg, NULL);
drivers/target/target_core_pr.c: * conditional checks for deve->pr_reg
pointer access complete.

so no need to any RCU magic here, it's never dereferences and can be
replace with a scalar, or probably better an atomic bitop.

>
> It also includes associated rcu_assign_pointer() + synchronize_rcu()
> in __core_scsi3_add_registration() and __core_scsi3_free_registration()
> for the RCU updater path.
>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Sagi Grimberg <sagig@mellanox.com>
> Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
> ---
> drivers/target/target_core_device.c | 1 +
> drivers/target/target_core_pr.c | 75 +++++++++++++++++++++++++++----------
> include/target/target_core_base.h | 4 +-
> 3 files changed, 59 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
> index 911758b..430d3d6 100644
> --- a/drivers/target/target_core_device.c
> +++ b/drivers/target/target_core_device.c
> @@ -448,6 +448,7 @@ int core_disable_device_list_for_node(
> * Disable struct se_dev_entry LUN ACL mapping
> */
> core_scsi3_ua_release_all(orig);
> + rcu_assign_pointer(orig->pr_reg, NULL);
> rcu_assign_pointer(orig->se_lun, NULL);
> rcu_assign_pointer(orig->se_lun_acl, NULL);
> orig->lun_flags = 0;
> diff --git a/drivers/target/target_core_pr.c b/drivers/target/target_core_pr.c
> index c0b593a..491043d 100644
> --- a/drivers/target/target_core_pr.c
> +++ b/drivers/target/target_core_pr.c
> @@ -327,9 +327,13 @@ static int core_scsi3_pr_seq_non_holder(
> int we = 0; /* Write Exclusive */
> int legacy = 0; /* Act like a legacy device and return
> * RESERVATION CONFLICT on some CDBs */
> + bool registered = false;
>
> rcu_read_lock();
> se_deve = target_nacl_find_deve(nacl, cmd->orig_fe_lun);
> + if (se_deve)
> + registered = (se_deve->pr_reg != NULL);
> + rcu_read_unlock();
> /*
> * Determine if the registration should be ignored due to
> * non-matching ISIDs in target_scsi3_pr_reservation_check().
> @@ -346,7 +350,7 @@ static int core_scsi3_pr_seq_non_holder(
> * Some commands are only allowed for the persistent reservation
> * holder.
> */
> - if ((se_deve->def_pr_registered) && !(ignore_reg))
> + if ((registered) && !(ignore_reg))
> registered_nexus = 1;
> break;
> case PR_TYPE_WRITE_EXCLUSIVE_REGONLY:
> @@ -356,7 +360,7 @@ static int core_scsi3_pr_seq_non_holder(
> * Some commands are only allowed for registered I_T Nexuses.
> */
> reg_only = 1;
> - if ((se_deve->def_pr_registered) && !(ignore_reg))
> + if ((registered) && !(ignore_reg))
> registered_nexus = 1;
> break;
> case PR_TYPE_WRITE_EXCLUSIVE_ALLREG:
> @@ -366,14 +370,12 @@ static int core_scsi3_pr_seq_non_holder(
> * Each registered I_T Nexus is a reservation holder.
> */
> all_reg = 1;
> - if ((se_deve->def_pr_registered) && !(ignore_reg))
> + if ((registered) && !(ignore_reg))
> registered_nexus = 1;
> break;
> default:
> - rcu_read_unlock();
> return -EINVAL;
> }
> - rcu_read_unlock();
> /*
> * Referenced from spc4r17 table 45 for *NON* PR holder access
> */
> @@ -1009,10 +1011,6 @@ static void __core_scsi3_dump_registration(
> pr_reg->pr_reg_aptpl);
> }
>
> -/*
> - * this function can be called with struct se_device->dev_reservation_lock
> - * when register_move = 1
> - */
> static void __core_scsi3_add_registration(
> struct se_device *dev,
> struct se_node_acl *nacl,
> @@ -1023,6 +1021,7 @@ static void __core_scsi3_add_registration(
> const struct target_core_fabric_ops *tfo = nacl->se_tpg->se_tpg_tfo;
> struct t10_pr_registration *pr_reg_tmp, *pr_reg_tmp_safe;
> struct t10_reservation *pr_tmpl = &dev->t10_pr;
> + struct se_dev_entry *deve;
>
> /*
> * Increment PRgeneration counter for struct se_device upon a successful
> @@ -1039,10 +1038,22 @@ static void __core_scsi3_add_registration(
>
> spin_lock(&pr_tmpl->registration_lock);
> list_add_tail(&pr_reg->pr_reg_list, &pr_tmpl->registration_list);
> - pr_reg->pr_reg_deve->def_pr_registered = 1;
>
> __core_scsi3_dump_registration(tfo, dev, nacl, pr_reg, register_type);
> spin_unlock(&pr_tmpl->registration_lock);
> +
> + mutex_lock(&nacl->lun_entry_mutex);
> + deve = target_nacl_find_deve(nacl, pr_reg->pr_res_mapped_lun);
> + if (deve)
> + rcu_assign_pointer(deve->pr_reg, pr_reg);
> + mutex_unlock(&nacl->lun_entry_mutex);
> +
> + /*
> + * Wait for read path critical RCU in core_scsi3_pr_seq_non_holder()
> + * conditional checks for deve->pr_reg pointer access complete.
> + */
> + synchronize_rcu();
> +
> /*
> * Skip extra processing for ALL_TG_PT=0 or REGISTER_AND_MOVE.
> */
> @@ -1054,6 +1065,8 @@ static void __core_scsi3_add_registration(
> */
> list_for_each_entry_safe(pr_reg_tmp, pr_reg_tmp_safe,
> &pr_reg->pr_reg_atp_list, pr_reg_atp_mem_list) {
> + struct se_node_acl *nacl_tmp = pr_reg_tmp->pr_reg_nacl;
> +
> list_del(&pr_reg_tmp->pr_reg_atp_mem_list);
>
> pr_reg_tmp->pr_res_generation = core_scsi3_pr_generation(dev);
> @@ -1061,13 +1074,23 @@ static void __core_scsi3_add_registration(
> spin_lock(&pr_tmpl->registration_lock);
> list_add_tail(&pr_reg_tmp->pr_reg_list,
> &pr_tmpl->registration_list);
> - pr_reg_tmp->pr_reg_deve->def_pr_registered = 1;
>
> - __core_scsi3_dump_registration(tfo, dev,
> - pr_reg_tmp->pr_reg_nacl, pr_reg_tmp,
> - register_type);
> + __core_scsi3_dump_registration(tfo, dev, nacl_tmp, pr_reg_tmp,
> + register_type);
> spin_unlock(&pr_tmpl->registration_lock);
>
> + mutex_lock(&nacl->lun_entry_mutex);
> + deve = target_nacl_find_deve(nacl_tmp, pr_reg_tmp->pr_res_mapped_lun);
> + if (deve)
> + rcu_assign_pointer(deve->pr_reg, pr_reg_tmp);
> + mutex_unlock(&nacl->lun_entry_mutex);
> +
> + /*
> + * Wait for read path critical RCU in core_scsi3_pr_seq_non_holder()
> + * conditional checks for deve->pr_reg pointer access complete.
> + */
> + synchronize_rcu();
> +
> /*
> * Drop configfs group dependency reference from
> * __core_scsi3_alloc_registration()
> @@ -1243,13 +1266,13 @@ static void __core_scsi3_free_registration(
> const struct target_core_fabric_ops *tfo =
> pr_reg->pr_reg_nacl->se_tpg->se_tpg_tfo;
> struct t10_reservation *pr_tmpl = &dev->t10_pr;
> + struct se_node_acl *nacl = pr_reg->pr_reg_nacl;
> + struct se_dev_entry *deve;
> char i_buf[PR_REG_ISID_ID_LEN];
>
> memset(i_buf, 0, PR_REG_ISID_ID_LEN);
> core_pr_dump_initiator_port(pr_reg, i_buf, PR_REG_ISID_ID_LEN);
>
> - pr_reg->pr_reg_deve->def_pr_registered = 0;
> - pr_reg->pr_reg_deve->pr_res_key = 0;
> if (!list_empty(&pr_reg->pr_reg_list))
> list_del(&pr_reg->pr_reg_list);
> /*
> @@ -1258,6 +1281,8 @@ static void __core_scsi3_free_registration(
> */
> if (dec_holders)
> core_scsi3_put_pr_reg(pr_reg);
> +
> + spin_unlock(&pr_tmpl->registration_lock);
> /*
> * Wait until all reference from any other I_T nexuses for this
> * *pr_reg have been released. Because list_del() is called above,
> @@ -1265,13 +1290,24 @@ static void __core_scsi3_free_registration(
> * count back to zero, and we release *pr_reg.
> */
> while (atomic_read(&pr_reg->pr_res_holders) != 0) {
> - spin_unlock(&pr_tmpl->registration_lock);
> pr_debug("SPC-3 PR [%s] waiting for pr_res_holders\n",
> tfo->get_fabric_name());
> cpu_relax();
> - spin_lock(&pr_tmpl->registration_lock);
> }
>
> + mutex_lock(&nacl->lun_entry_mutex);
> + deve = target_nacl_find_deve(nacl, pr_reg->pr_res_mapped_lun);
> + if (deve)
> + rcu_assign_pointer(deve->pr_reg, NULL);
> + mutex_unlock(&nacl->lun_entry_mutex);
> +
> + /*
> + * Wait for read path critical RCU in core_scsi3_pr_seq_non_holder()
> + * conditional checks for deve->pr_reg pointer access complete.
> + */
> + synchronize_rcu();
> +
> + spin_lock(&pr_tmpl->registration_lock);
> pr_debug("SPC-3 PR [%s] Service Action: UNREGISTER Initiator"
> " Node: %s%s\n", tfo->get_fabric_name(),
> pr_reg->pr_reg_nacl->initiatorname,
> @@ -3428,13 +3464,14 @@ after_iport_check:
> dest_pr_reg = __core_scsi3_locate_pr_reg(dev, dest_node_acl,
> iport_ptr);
> if (!dest_pr_reg) {
> + spin_unlock(&dev->dev_reservation_lock);
> if (core_scsi3_alloc_registration(cmd->se_dev,
> dest_node_acl, dest_se_deve, iport_ptr,
> sa_res_key, 0, aptpl, 2, 1)) {
> - spin_unlock(&dev->dev_reservation_lock);
> ret = TCM_INVALID_PARAMETER_LIST;
> goto out;
> }
> + spin_lock(&dev->dev_reservation_lock);
> dest_pr_reg = __core_scsi3_locate_pr_reg(dev, dest_node_acl,
> iport_ptr);
> new_reg = 1;
> diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
> index 1b06d27..2f0c830 100644
> --- a/include/target/target_core_base.h
> +++ b/include/target/target_core_base.h
> @@ -640,7 +640,6 @@ struct se_lun_acl {
> };
>
> struct se_dev_entry {
> - bool def_pr_registered;
> /* See transport_lunflags_table */
> u32 lun_flags;
> u32 mapped_lun;
> @@ -657,7 +656,8 @@ struct se_dev_entry {
> struct se_node_acl *se_node_acl;
> struct se_lun_acl __rcu *se_lun_acl;
> spinlock_t ua_lock;
> - struct se_lun *se_lun;
> + struct se_lun __rcu *se_lun;
> + struct t10_pr_registration __rcu *pr_reg;
> struct list_head alua_port_list;
> struct list_head ua_list;
> struct hlist_node link;
> --
> 1.9.1
---end quoted text---