Re: [PATCH 2/2] libsas: Enhance libsas hotplug

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Hi,

There are some comments, inline.

In general, if it works, it looks ok.

Other reviews would be greatly appreciated - Hannes, Christoph, Johannes, Dan - please.

> Libsas complete a hotplug event notified by LLDD in several works,
> for example, if libsas receive a PHYE_LOSS_OF_SIGNAL, we process it
> in following steps:
>
> notify_phy_event    [interrupt context]
>     sas_queue_event        [queue work on shost->work_q]
>         sas_phye_loss_of_signal        [running in shost->work_q]
>             sas_deform_port        [remove sas port]
>                 sas_unregister_dev
> sas_discover_event [queue destruct work on shost->work_q tail]
>
> In above case, complete whole hotplug in two works, remove sas port first, then > put the destruction of device in another work and queue it on in the tail of > workqueue, since sas port is the parent of the children rphy device, so if remove > sas port first, the children rphy device would also be deleted, when the destruction > work coming, it would find the target has been removed already, and report a
> sysfs warning calltrace.
>
> queue tail                                             queue head
> DISCE_DESTRUCT----> PORTE_BYTES_DMAED event ----->PHYE_LOSS_OF_SIGNAL[running]
>
> There are other hotplug issues in current framework, in above case, if there is > hotadd sas event queued between hotremove works, the hotplug order would be broken
> and unexpected issues would happen.
>
> In this patch, we try to solve these issues in following steps:
> 1. create a new workqueue used to run sas event work, instead of scsi host workqueue, > because we may block sas event work, we cannot block the normal scsi works.

What do we block the event work for?

> 2. create a new workqueue used to run sas discovery events work, instead of scsi host > workqueue, because in some cases, eg. in revalidate domain event, we may unregister > a sas device and discover new one, we must sync the execution, wait the remove process > finish, then start a new discovery. So we must put the probe and destruct discovery
>    events in a new workqueue to avoid deadlock.
> 3. introudce a asd_sas_port level wait-complete and a sas_discovery level wait-complete > we use former wait-complete to achieve a sas event atomic process and use latter to
>    make a sas discovery sync.
> 4. remove disco_mutex in sas_revalidate_domain, since now sas_revalidate_domain sync > the destruct discovery event execution, it's no need to lock disco mutex there.
>
> Signed-off-by: Yijing Wang <wangyijing@xxxxxxxxxx>
> ---
> drivers/scsi/libsas/sas_discover.c | 58 ++++++++++++++++++++++++++++----------
>  drivers/scsi/libsas/sas_event.c    |  2 +-
>  drivers/scsi/libsas/sas_expander.c |  9 +++++-
>  drivers/scsi/libsas/sas_init.c     | 31 +++++++++++++++++++-
>  drivers/scsi/libsas/sas_internal.h | 50 ++++++++++++++++++++++++++++++++
>  drivers/scsi/libsas/sas_port.c     |  4 +++
>  include/scsi/libsas.h              | 11 +++++++-
>  7 files changed, 146 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/scsi/libsas/sas_discover.c b/drivers/scsi/libsas/sas_discover.c
> index 60de662..43e8a1e 100644
> --- a/drivers/scsi/libsas/sas_discover.c
> +++ b/drivers/scsi/libsas/sas_discover.c
> @@ -503,11 +503,10 @@ static void sas_revalidate_domain(struct work_struct *work)
>      struct domain_device *ddev = port->port_dev;
>
>      /* prevent revalidation from finding sata links in recovery */
> -    mutex_lock(&ha->disco_mutex);
>      if (test_bit(SAS_HA_ATA_EH_ACTIVE, &ha->state)) {
>          SAS_DPRINTK("REVALIDATION DEFERRED on port %d, pid:%d\n",
>                  port->id, task_pid_nr(current));
> -        goto out;
> +        return;
>      }
>
>      clear_bit(DISCE_REVALIDATE_DOMAIN, &port->disc.pending);
> @@ -521,20 +520,57 @@ static void sas_revalidate_domain(struct work_struct *work)
>
> SAS_DPRINTK("done REVALIDATING DOMAIN on port %d, pid:%d, res 0x%x\n",
>              port->id, task_pid_nr(current), res);
> - out:
> -    mutex_unlock(&ha->disco_mutex);
> +}
> +
> +static const work_func_t sas_event_fns[DISC_NUM_EVENTS] = {
> +    [DISCE_DISCOVER_DOMAIN] = sas_discover_domain,
> +    [DISCE_REVALIDATE_DOMAIN] = sas_revalidate_domain,
> +    [DISCE_PROBE] = sas_probe_devices,
> +    [DISCE_SUSPEND] = sas_suspend_devices,
> +    [DISCE_RESUME] = sas_resume_devices,
> +    [DISCE_DESTRUCT] = sas_destruct_devices,
> +};
> +
> +/* a simple wrapper for sas discover event funtions */
> +static void sas_discover_common_fn(struct work_struct *work)
> +{
> +    struct sas_discovery_event *ev = to_sas_discovery_event(work);
> +    struct asd_sas_port *port = ev->port;
> +
> +    sas_event_fns[ev->type](work);
> +    sas_unbusy_port(port);
>  }
>
>  /* ---------- Events ---------- */
>
> static void sas_chain_work(struct sas_ha_struct *ha, struct sas_work *sw)
>  {
> +    int ret;
> +    struct sas_discovery_event *ev = to_sas_discovery_event(&sw->work);
> +    struct asd_sas_port *port = ev->port;
> +
>      /* chained work is not subject to SA_HA_DRAINING or
>       * SAS_HA_REGISTERED, because it is either submitted in the
>       * workqueue, or known to be submitted from a context that is
>       * not racing against draining
>       */

Is this comment still valid (even if you have not touched the drain logic work)?

> -    scsi_queue_work(ha->core.shost, &sw->work);
> +    sas_busy_port(port);
> +
> +    /*
> +     * discovery event probe and destruct would be called in other
> +     * discovery event like discover domain and revalidate domain
> +     * events, in some cases, we need to sync execute probe and destruct
> +     * events, so run discover events except probe/destruct in a new
> +     * workqueue.
> +     */
> +    if (ev->type == DISCE_PROBE || ev->type == DISCE_DESTRUCT)
> +        ret = scsi_queue_work(ha->core.shost, &sw->work);
> +    else
> +        ret = queue_work(ha->disc_q, &sw->work);
> +
> +    if (ret != 1)
> +        /* queue a work fail, unbusy the ha before return */
> +        sas_unbusy_port(port);

Do we really need to check for this error case, since we have dynamic work structs (I think queue_work only fails if we try requeuing a work item)?

>  }
>
>  static void sas_chain_event(int event, unsigned long *pending,
> @@ -575,18 +611,10 @@ void sas_init_disc(struct sas_discovery *disc, struct asd_sas_port *port)
>  {
>      int i;
>
> -    static const work_func_t sas_event_fns[DISC_NUM_EVENTS] = {
> -        [DISCE_DISCOVER_DOMAIN] = sas_discover_domain,
> -        [DISCE_REVALIDATE_DOMAIN] = sas_revalidate_domain,
> -        [DISCE_PROBE] = sas_probe_devices,
> -        [DISCE_SUSPEND] = sas_suspend_devices,
> -        [DISCE_RESUME] = sas_resume_devices,
> -        [DISCE_DESTRUCT] = sas_destruct_devices,
> -    };
> -
>      disc->pending = 0;
>      for (i = 0; i < DISC_NUM_EVENTS; i++) {
> -        INIT_SAS_WORK(&disc->disc_work[i].work, sas_event_fns[i]);
> +        INIT_SAS_WORK(&disc->disc_work[i].work, sas_discover_common_fn);
>          disc->disc_work[i].port = port;
> +        disc->disc_work[i].type = i;
>      }
>  }
> diff --git a/drivers/scsi/libsas/sas_event.c b/drivers/scsi/libsas/sas_event.c
> index 06c5c4b..c0fc07d 100644
> --- a/drivers/scsi/libsas/sas_event.c
> +++ b/drivers/scsi/libsas/sas_event.c
> @@ -41,7 +41,7 @@ void sas_queue_work(struct sas_ha_struct *ha, struct sas_work *sw)
>          if (list_empty(&sw->drain_node))
>              list_add(&sw->drain_node, &ha->defer_q);
>      } else
> -        scsi_queue_work(ha->core.shost, &sw->work);
> +        queue_work(ha->event_q, &sw->work);
>  }
>
>  static void sas_queue_event(int event, struct sas_work *work,
> diff --git a/drivers/scsi/libsas/sas_expander.c b/drivers/scsi/libsas/sas_expander.c
> index 570b2cb..a8c8ae1 100644
> --- a/drivers/scsi/libsas/sas_expander.c
> +++ b/drivers/scsi/libsas/sas_expander.c
> @@ -822,7 +822,9 @@ static struct domain_device *sas_ex_discover_end_dev(
>
> list_add_tail(&child->disco_list_node, &parent->port->disco_list);
>
> +        wait_discover_event_init(child->port);
>          res = sas_discover_sata(child);
> +        wait_for_discover_event_finish(child->port);
>          if (res) {
>              SAS_DPRINTK("sas_discover_sata() for device %16llx at "
>                      "%016llx:0x%x returned 0x%x\n",
> @@ -847,7 +849,9 @@ static struct domain_device *sas_ex_discover_end_dev(
>
> list_add_tail(&child->disco_list_node, &parent->port->disco_list);
>
> +        wait_discover_event_init(child->port);
>          res = sas_discover_end_dev(child);

In sas_discover_end_dev(), we may return before sending the queue event (if LLDD notify dev found returns error), we please take care of this.

> +        wait_for_discover_event_finish(child->port);
>          if (res) {
>              SAS_DPRINTK("sas_discover_end_dev() for device %16llx "
>                      "at %016llx:0x%x returned 0x%x\n",
> @@ -1890,8 +1894,11 @@ static void sas_unregister_devs_sas_addr(struct domain_device *parent,
>                  if (child->dev_type == SAS_EDGE_EXPANDER_DEVICE ||
>                      child->dev_type == SAS_FANOUT_EXPANDER_DEVICE)
>                      sas_unregister_ex_tree(parent->port, child);
> -                else
> +                else {
> +                    wait_discover_event_init(parent->port);
>                      sas_unregister_dev(parent->port, child);
> +                    wait_for_discover_event_finish(parent->port);
> +                }
>                  found = child;
>                  break;
>              }
> diff --git a/drivers/scsi/libsas/sas_init.c b/drivers/scsi/libsas/sas_init.c
> index 79f95d0..1c49483 100644
> --- a/drivers/scsi/libsas/sas_init.c
> +++ b/drivers/scsi/libsas/sas_init.c
> @@ -38,6 +38,8 @@
>
>  #include "../scsi_sas_internal.h"
>
> +static DEFINE_IDA(sas_ida);
> +
>  static struct kmem_cache *sas_task_cache;
>
>  struct sas_task *sas_alloc_task(gfp_t flags)
> @@ -116,6 +118,7 @@ void sas_hae_reset(struct work_struct *work)
>  int sas_register_ha(struct sas_ha_struct *sas_ha)
>  {
>      int error = 0;
> +    char name[64];
>
>      mutex_init(&sas_ha->disco_mutex);
>      spin_lock_init(&sas_ha->phy_port_lock);
> @@ -146,6 +149,30 @@ int sas_register_ha(struct sas_ha_struct *sas_ha)
>          goto Undo_ports;
>      }
>
> +    sas_ha->id = ida_simple_get(&sas_ida, 0, 0, GFP_KERNEL);
> +    if(sas_ha->id < 0)
> +        goto Undo_ports;
> +
> +    memset(name, 0, 64);

Why memset and then sprintf?

> +    snprintf(name, 64, "sas-event-%d", sas_ha->id);

Can you just use unique dev_name(sas_ha->dev) to help form this name, so that you don't have to introduce IDR?

> +    sas_ha->event_q = create_singlethread_workqueue(name);
> +
> +    /*
> +     * sas-disc-xx workqueue run the discover work except
> +     * probe and destruct.
> +     */
> +    snprintf(name, 64, "sas-disc-%d", sas_ha->id);
> +    sas_ha->disc_q = create_singlethread_workqueue(name);
> +    if(!sas_ha->event_q || !sas_ha->disc_q) {
> +        ida_simple_remove(&sas_ida, sas_ha->id);
> +        if (sas_ha->event_q)
> +            destroy_workqueue(sas_ha->event_q);
> +        if (sas_ha->disc_q)
> +            destroy_workqueue(sas_ha->disc_q);

Can this error handling be a bit more concise?

> +        goto Undo_ports;
> +    }
> +
> +
>      INIT_LIST_HEAD(&sas_ha->eh_done_q);
>      INIT_LIST_HEAD(&sas_ha->eh_ata_q);
>
> @@ -181,6 +208,9 @@ int sas_unregister_ha(struct sas_ha_struct *sas_ha)
>      __sas_drain_work(sas_ha);
>      mutex_unlock(&sas_ha->drain_mutex);
>
> +    destroy_workqueue(sas_ha->event_q);
> +    destroy_workqueue(sas_ha->disc_q);
> +    ida_simple_remove(&sas_ida, sas_ha->id);
>      return 0;
>  }
>
> @@ -568,7 +598,6 @@ void sas_domain_release_transport(struct scsi_transport_template *stt)
>  EXPORT_SYMBOL_GPL(sas_domain_release_transport);
>
>  /* ---------- SAS Class register/unregister ---------- */
> -
>  static int __init sas_class_init(void)
>  {
>      sas_task_cache = KMEM_CACHE(sas_task, SLAB_HWCACHE_ALIGN);
> diff --git a/drivers/scsi/libsas/sas_internal.h b/drivers/scsi/libsas/sas_internal.h
> index 33ce7e5..276df8e 100644
> --- a/drivers/scsi/libsas/sas_internal.h
> +++ b/drivers/scsi/libsas/sas_internal.h
> @@ -100,6 +100,56 @@ void sas_free_device(struct kref *kref);
>  extern const work_func_t sas_phy_event_fns[PHY_NUM_EVENTS];
>  extern const work_func_t sas_port_event_fns[PORT_NUM_EVENTS];
>
> +static inline void wait_discover_event_init(struct asd_sas_port *port)

You need to change function names to have "sas" prefix. Actually these functions are all a bit messy.

> +{
> +    if (port) {

This init and wait function are currently act ask bookend wrappers. I think it may be better to put them in the wrapped function (if possible), as:
a. probably then we don't need port NULL check
b. handles situations where event is possibly not queued, like the suspected sas_discover_end_dev()

> +        init_completion(&port->disc.completion);
> +        port->disc.wait = 1;
> +    }
> +}
> +
> +static inline void wait_for_discover_event_finish(
> +        struct asd_sas_port *port)
> +{
> +    if (port && port->disc.wait == 1)

Can you just use completion_done() instead of introducing another variable in discovery_event.wait?

> +        wait_for_completion(&port->disc.completion);
> +}
> +
> +static inline void wait_sas_event_init(struct asd_sas_port *port)
> +{
> +    if (port) {
> +        init_completion(&port->completion);
> +        port->busy = 0;
> +    }
> +}
> +
> +static inline void wait_for_sas_event_finish(
> +        struct asd_sas_port *port)
> +{
> +    if (port && port->busy)
> +        wait_for_completion(&port->completion);
> +}
> +
> +static inline void sas_busy_port(struct asd_sas_port *port)
> +{
> +    if (port)
> +        port->busy++;

Why not use kref?

> +}
> +
> +static inline void sas_unbusy_port(struct asd_sas_port *port)
> +{
> +    if (port && (port->busy > 0)) {
> +        port->busy--;
> +        if (!port->busy)
> +            complete(&port->completion);
> +    }
> +
> +    if (port && (port->disc.wait == 1)) {

Why check port twice?

> +        complete(&port->disc.completion);
> +        port->disc.wait = 0;
> +    }
> +}
> +
>  #ifdef CONFIG_SCSI_SAS_HOST_SMP
> extern int sas_smp_host_handler(struct Scsi_Host *shost, struct request *req,
>                  struct request *rsp);
> diff --git a/drivers/scsi/libsas/sas_port.c b/drivers/scsi/libsas/sas_port.c
> index 9326628..8d8b38c 100644
> --- a/drivers/scsi/libsas/sas_port.c
> +++ b/drivers/scsi/libsas/sas_port.c
> @@ -191,7 +191,9 @@ static void sas_form_port(struct asd_sas_phy *phy)
>      if (si->dft->lldd_port_formed)
>          si->dft->lldd_port_formed(phy);
>
> +    wait_sas_event_init(port);
>      sas_discover_event(phy->port, DISCE_DISCOVER_DOMAIN);
> +    wait_for_sas_event_finish(port);

Is it neater to put these calls inside sas_discover_event()?

>  }
>
>  /**
> @@ -218,7 +220,9 @@ void sas_deform_port(struct asd_sas_phy *phy, int gone)
>          dev->pathways--;
>
>      if (port->num_phys == 1) {
> +        wait_sas_event_init(port);
>          sas_unregister_domain_devices(port, gone);
> +        wait_for_sas_event_finish(port);
>          sas_port_delete(port->port);
>          port->port = NULL;
>      } else {
> diff --git a/include/scsi/libsas.h b/include/scsi/libsas.h
> index c4444ad..4b931d4 100644
> --- a/include/scsi/libsas.h
> +++ b/include/scsi/libsas.h
> @@ -240,6 +240,9 @@ static inline void INIT_SAS_WORK(struct sas_work *sw, void (*fn)(struct work_str
>  struct sas_discovery_event {
>      struct sas_work work;
>      struct asd_sas_port *port;
> +    enum discover_event    type;
> +    int wait;
> +    struct completion completion;
>  };
>
> static inline struct sas_discovery_event *to_sas_discovery_event(struct work_struct *work)
> @@ -256,6 +259,8 @@ struct sas_discovery {
>      u8     eeds_a[8];
>      u8     eeds_b[8];
>      int    max_level;
> +    int    wait;
> +    struct completion completion;

Again, does completion_done() do the same job as wait element?

>  };
>
>  /* The port struct is Class:RW, driver:RO */
> @@ -276,7 +281,8 @@ struct asd_sas_port {
>
>  /* public: */
>      int id;
> -
> +    int busy;
> +    struct completion completion;

I think public means LLDD can access, which is not the case

>      enum sas_class   class;
>      u8               sas_addr[SAS_ADDR_SIZE];
>      u8               attached_sas_addr[SAS_ADDR_SIZE];
> @@ -387,6 +393,7 @@ struct sas_ha_struct {
>      int          eh_active;
>      wait_queue_head_t eh_wait_q;
>      struct list_head  eh_dev_q;
> +    int       id; /* for create workqueue */
>
>      struct mutex disco_mutex;
>
> @@ -396,6 +403,8 @@ struct sas_ha_struct {
>      char *sas_ha_name;
>      struct device *dev;      /* should be set */
>      struct module *lldd_module; /* should be set */
> +    struct workqueue_struct    *event_q;
> +    struct workqueue_struct    *disc_q;
>
>      u8 *sas_addr;          /* must be set */
>      u8 hashed_sas_addr[HASHED_SAS_ADDR_SIZE];
>




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