On Thu, 2017-02-09 at 08:06 +0100, Hannes Reinecke wrote:
> On 02/08/2017 11:24 PM, 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>
> > ---
> > 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;
> >
> >
>
> What a curious construct.
> Why not a normal kref here?
> Using an atomic here would make sense if you need to bail out if both
> counters would be independent.
> But as it stands the 'tgt_kref' _has_ to be '0' before the final call to
> __target_put_sess_cmd() (otherwise you'll end up with a hanging
> wait_for_completion).
> Which means that the lifetime of 'tgt_kref' is bounded by the lifetime
> of se_cmd, and we can just add a second kref there.
Although that will result in more code, I will change the atomic_t into a
kref_t.
Bart.--
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