Re: [PATCH 03/31] Protect SCSI device state changes with a mutex

[Bart Van Assche]

On Wed, 2017-05-24 at 07:51 +0200, Hannes Reinecke wrote:
> On 05/24/2017 02:33 AM, Bart Van Assche wrote:
> > Enable this mechanism for all scsi_target_*block() callers but not
> > for the scsi_internal_device_unblock() calls from the mpt3sas driver
> > because that driver can call scsi_internal_device_unblock() from
> > atomic context.
> > 
> > Signed-off-by: Bart Van Assche 
> > Cc: Christoph Hellwig 
> > Cc: Hannes Reinecke 
> > Cc: Johannes Thumshirn 
> > ---
> >  drivers/scsi/scsi_error.c |  8 +++-
> >  drivers/scsi/scsi_lib.c   | 27 +--
> >  drivers/scsi/scsi_scan.c  | 16 +---
> >  drivers/scsi/scsi_sysfs.c | 24 +++-
> >  drivers/scsi/scsi_transport_srp.c |  7 ---
> >  drivers/scsi/sd.c |  7 +--
> >  include/scsi/scsi_device.h|  1 +
> >  7 files changed, 66 insertions(+), 24 deletions(-)
> > 
> 
> [ .. ]
> > diff --git a/drivers/scsi/scsi_transport_srp.c 
> > b/drivers/scsi/scsi_transport_srp.c
> > index 3c5d89852e9f..f617021c94f7 100644
> > --- a/drivers/scsi/scsi_transport_srp.c
> > +++ b/drivers/scsi/scsi_transport_srp.c
> > @@ -554,11 +554,12 @@ int srp_reconnect_rport(struct srp_rport *rport)
> >  * invoking scsi_target_unblock() won't change the state of
> >  * these devices into running so do that explicitly.
> >  */
> > -   spin_lock_irq(shost->host_lock);
> > -   __shost_for_each_device(sdev, shost)
> > +   shost_for_each_device(sdev, shost) {
> > +   mutex_lock(>state_mutex);
> > if (sdev->sdev_state == SDEV_OFFLINE)
> > sdev->sdev_state = SDEV_RUNNING;
> > -   spin_unlock_irq(shost->host_lock);
> > +   mutex_unlock(>state_mutex);
> > +   }
> > } else if (rport->state == SRP_RPORT_RUNNING) {
> > /*
> >  * srp_reconnect_rport() has been invoked with fast_io_fail
> 
> Why do you drop the host lock here? I thought that the host lock is
> needed to protect shost_for_each_device()?

Hello Hannes,

The only purpose of holding the host lock was to protect the SCSI device list
iteration by __shost_for_each_device(). shost_for_each_device() obtains that
lock itself. From :

#define shost_for_each_device(sdev, shost) \
for ((sdev) = __scsi_iterate_devices((shost), NULL); \
 (sdev); \
 (sdev) = __scsi_iterate_devices((shost), (sdev)))

>From drivers/scsi/scsi.c:

struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
   struct scsi_device *prev)
{
struct list_head *list = (prev ? >siblings : >__devices);
struct scsi_device *next = NULL;
unsigned long flags;

spin_lock_irqsave(shost->host_lock, flags);
while (list->next != >__devices) {
next = list_entry(list->next, struct scsi_device, siblings);
/* skip devices that we can't get a reference to */
if (!scsi_device_get(next))
break;
next = NULL;
list = list->next;
}
spin_unlock_irqrestore(shost->host_lock, flags);

if (prev)
scsi_device_put(prev);
return next;
}

Bart.

Re: [PATCH 03/31] Protect SCSI device state changes with a mutex

[Hannes Reinecke]

On 05/24/2017 02:33 AM, Bart Van Assche wrote:
> Enable this mechanism for all scsi_target_*block() callers but not
> for the scsi_internal_device_unblock() calls from the mpt3sas driver
> because that driver can call scsi_internal_device_unblock() from
> atomic context.
> 
> Signed-off-by: Bart Van Assche 
> Cc: Christoph Hellwig 
> Cc: Hannes Reinecke 
> Cc: Johannes Thumshirn 
> ---
>  drivers/scsi/scsi_error.c |  8 +++-
>  drivers/scsi/scsi_lib.c   | 27 +--
>  drivers/scsi/scsi_scan.c  | 16 +---
>  drivers/scsi/scsi_sysfs.c | 24 +++-
>  drivers/scsi/scsi_transport_srp.c |  7 ---
>  drivers/scsi/sd.c |  7 +--
>  include/scsi/scsi_device.h|  1 +
>  7 files changed, 66 insertions(+), 24 deletions(-)
> 
[ .. ]
> diff --git a/drivers/scsi/scsi_transport_srp.c 
> b/drivers/scsi/scsi_transport_srp.c
> index 3c5d89852e9f..f617021c94f7 100644
> --- a/drivers/scsi/scsi_transport_srp.c
> +++ b/drivers/scsi/scsi_transport_srp.c
> @@ -554,11 +554,12 @@ int srp_reconnect_rport(struct srp_rport *rport)
>* invoking scsi_target_unblock() won't change the state of
>* these devices into running so do that explicitly.
>*/
> - spin_lock_irq(shost->host_lock);
> - __shost_for_each_device(sdev, shost)
> + shost_for_each_device(sdev, shost) {
> + mutex_lock(>state_mutex);
>   if (sdev->sdev_state == SDEV_OFFLINE)
>   sdev->sdev_state = SDEV_RUNNING;
> - spin_unlock_irq(shost->host_lock);
> + mutex_unlock(>state_mutex);
> + }
>   } else if (rport->state == SRP_RPORT_RUNNING) {
>   /*
>* srp_reconnect_rport() has been invoked with fast_io_fail
Why do you drop the host lock here? I thought that the host lock is
needed to protect shost_for_each_device()?

Cheers,

Hannes
-- 
Dr. Hannes ReineckeTeamlead Storage & Networking
h...@suse.de   +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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