On Wed, 2017-02-08 at 14:24 -0800, Bart Van Assche wrote:
> This reference count keeps track of the number of references held
> by a target driver on a command. se_cmd.complete is set once the
> target driver has released all references it held on a command.
>
> Signed-off-by: Bart Van Assche <bart.vanassche@xxxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Andy Grover <agrover@xxxxxxxxxx>
> Cc: David Disseldorp <ddiss@xxxxxxx>
> ---
I'm strongly opposed to adding another reference count and struct
completion to every se_cmd, and using a special version of
__target_put_sess_cmd() sprinkled all over the place.
We've already got a se_cmd->cmd_kref, se_cmd->t_transport_stop_comp used
for se_cmd quiesce (CMD_T_STOP) during CMD_T_ABORT and
transport_generic_free_cmd() shutdown, and se_cmd->cmd_wait_set for
drivers doing active I/O shutdown via target_sess_cmd_list_set_waiting.
Adding a new reference count, a third struct completion, and fast path
complete_all() for everyone (not just CMD_T_ABORT) just to get rid of
se_cmd->cmd_wait_set doesn't simplify anything.
So that said, dropping this patch until you can figure out how to use
the single existing se_cmd->cmd_kref.
> drivers/target/target_core_internal.h | 1 +
> drivers/target/target_core_tmr.c | 8 ++++----
> drivers/target/target_core_transport.c | 24 +++++++++++++++++++++---
> include/target/target_core_base.h | 2 ++
> 4 files changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/target/target_core_internal.h b/drivers/target/target_core_internal.h
> index 9ab7090f7c83..48de996ad28d 100644
> --- a/drivers/target/target_core_internal.h
> +++ b/drivers/target/target_core_internal.h
> @@ -146,6 +146,7 @@ int transport_dump_vpd_assoc(struct t10_vpd *, unsigned char *, int);
> int transport_dump_vpd_ident_type(struct t10_vpd *, unsigned char *, int);
> int transport_dump_vpd_ident(struct t10_vpd *, unsigned char *, int);
> void transport_clear_lun_ref(struct se_lun *);
> +int __target_put_sess_cmd(struct se_cmd *se_cmd);
> void transport_send_task_abort(struct se_cmd *);
> sense_reason_t target_cmd_size_check(struct se_cmd *cmd, unsigned int size);
> void target_qf_do_work(struct work_struct *work);
> diff --git a/drivers/target/target_core_tmr.c b/drivers/target/target_core_tmr.c
> index 367799b4dde1..161c8b8482db 100644
> --- a/drivers/target/target_core_tmr.c
> +++ b/drivers/target/target_core_tmr.c
> @@ -188,7 +188,7 @@ void core_tmr_abort_task(
> if (!tmr->tmr_dev &&
> transport_lookup_tmr_lun(tmr->task_cmd,
> se_cmd->orig_fe_lun) < 0) {
> - target_put_sess_cmd(se_cmd);
> + __target_put_sess_cmd(se_cmd);
> continue;
> }
>
> @@ -199,7 +199,7 @@ void core_tmr_abort_task(
> transport_wait_for_tasks(se_cmd);
>
> transport_cmd_finish_abort(se_cmd, true);
> - target_put_sess_cmd(se_cmd);
> + __target_put_sess_cmd(se_cmd);
>
> printk("ABORT_TASK: Sending TMR_FUNCTION_COMPLETE for"
> " ref_tag: %llu\n", ref_tag);
> @@ -299,7 +299,7 @@ static void core_tmr_drain_tmr_list(
> transport_wait_for_tasks(cmd);
>
> transport_cmd_finish_abort(cmd, 1);
> - target_put_sess_cmd(cmd);
> + __target_put_sess_cmd(cmd);
> }
> }
>
> @@ -398,7 +398,7 @@ static void core_tmr_drain_state_list(
> transport_wait_for_tasks(cmd);
>
> core_tmr_handle_tas_abort(cmd, tas);
> - target_put_sess_cmd(cmd);
> + __target_put_sess_cmd(cmd);
> }
> }
>
> diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
> index 8f2169e92771..533b584c2806 100644
> --- a/drivers/target/target_core_transport.c
> +++ b/drivers/target/target_core_transport.c
> @@ -1217,6 +1217,7 @@ void transport_init_se_cmd(
> init_completion(&cmd->cmd_wait_comp);
> spin_lock_init(&cmd->t_state_lock);
> kref_init(&cmd->cmd_kref);
> + atomic_set(&cmd->tgt_ref, 1);
> cmd->transport_state = CMD_T_DEV_ACTIVE;
>
> cmd->se_tfo = tfo;
> @@ -2554,6 +2555,7 @@ int target_get_sess_cmd(struct se_cmd *se_cmd, bool ack_kref)
> if (!kref_get_unless_zero(&se_cmd->cmd_kref))
> return -EINVAL;
>
> + atomic_inc(&se_cmd->tgt_ref);
> se_cmd->se_cmd_flags |= SCF_ACK_KREF;
> }
>
> @@ -2590,6 +2592,8 @@ static void target_release_cmd_kref(struct kref *kref)
> unsigned long flags;
> bool fabric_stop;
>
> + WARN_ON_ONCE(atomic_read(&se_cmd->tgt_ref) != 0);
> +
> if (se_sess) {
> spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
>
> @@ -2614,15 +2618,29 @@ static void target_release_cmd_kref(struct kref *kref)
> }
>
> /**
> + * __target_put_sess_cmd - drop a reference obtained by kref_get_unless_zero()
> + */
> +int __target_put_sess_cmd(struct se_cmd *se_cmd)
> +{
> + return kref_put(&se_cmd->cmd_kref, target_release_cmd_kref);
> +}
> +
> +/**
> * target_put_sess_cmd - decrease the command reference count
> - * @se_cmd: command to drop a reference from
> + * @se_cmd: Drop a reference obtained by target_get_sess_cmd().
> *
> * Returns 1 if and only if this target_put_sess_cmd() call caused the
> * refcount to drop to zero. Returns zero otherwise.
> */
> int target_put_sess_cmd(struct se_cmd *se_cmd)
> {
> - return kref_put(&se_cmd->cmd_kref, target_release_cmd_kref);
> + long ref = atomic_dec_return(&se_cmd->tgt_ref);
> +
> + WARN_ON_ONCE(ref < 0);
> + if (ref == 0)
> + complete(&se_cmd->complete);
> +
> + return __target_put_sess_cmd(se_cmd);
> }
> EXPORT_SYMBOL(target_put_sess_cmd);
>
> @@ -2680,7 +2698,7 @@ void target_wait_for_sess_cmds(struct se_session *se_sess)
> tas = (se_cmd->transport_state & CMD_T_TAS);
> spin_unlock_irqrestore(&se_cmd->t_state_lock, flags);
>
> - if (!target_put_sess_cmd(se_cmd)) {
> + if (!__target_put_sess_cmd(se_cmd)) {
> if (tas)
> target_put_sess_cmd(se_cmd);
> }
> diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
> index fb87f0e5d0d6..c84e5eecb94d 100644
> --- a/include/target/target_core_base.h
> +++ b/include/target/target_core_base.h
> @@ -495,7 +495,9 @@ struct se_cmd {
> #define CMD_T_FABRIC_STOP (1 << 11)
> spinlock_t t_state_lock;
> struct kref cmd_kref;
> + atomic_t tgt_ref;
> struct completion t_transport_stop_comp;
> + struct completion complete;
>
> struct work_struct work;
>
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