Re: [PATCH v3 18/18] ibmvfc: drop host lock when completing commands in CRQ

2020-12-04 Thread Tyrel Datwyler 
On 12/4/20 1:35 PM, Brian King wrote:
> On 12/2/20 8:08 PM, Tyrel Datwyler wrote:
>> The legacy CRQ holds the host lock the even while completing commands.
>> This presents a problem when in legacy single queue mode and
>> nr_hw_queues is greater than one since calling scsi_done() introduces
>> the potential for deadlock.
>>
>> If nr_hw_queues is greater than one drop the hostlock in the legacy CRQ
>> path when completing a command.
>>
>> Signed-off-by: Tyrel Datwyler 
>> ---
>>  drivers/scsi/ibmvscsi/ibmvfc.c | 8 +++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
>> index e499599662ec..e2200bdff2be 100644
>> --- a/drivers/scsi/ibmvscsi/ibmvfc.c
>> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c
>> @@ -2969,6 +2969,7 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, 
>> struct ibmvfc_host *vhost)
>>  {
>>  long rc;
>>  struct ibmvfc_event *evt = (struct ibmvfc_event 
>> *)be64_to_cpu(crq->ioba);
>> +unsigned long flags;
>>  
>>  switch (crq->valid) {
>>  case IBMVFC_CRQ_INIT_RSP:
>> @@ -3039,7 +3040,12 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, 
>> struct ibmvfc_host *vhost)
>>  del_timer(>timer);
>>  list_del(>queue);
>>  ibmvfc_trc_end(evt);
>> -evt->done(evt);
>> +if (nr_scsi_hw_queues > 1) {
>> +spin_unlock_irqrestore(vhost->host->host_lock, flags);
>> +evt->done(evt);
>> +spin_lock_irqsave(vhost->host->host_lock, flags);
>> +} else
>> +evt->done(evt);
> 
> Similar comment here as previously. The flags parameter is an output for
> spin_lock_irqsave but an input for spin_unlock_irqrestore. You'll need
> to rethink the locking here. You could just do a spin_unlock_irq / 
> spin_lock_irq
> here and that would probably be OK, but probably isn't the best. 
> 

Yeah, this will also get its own lock and flags saved in the per-queue struct in
the next spin.

-Tyrel

>>  }
>>  
>>  /**
>>
> 
>

Re: [PATCH v3 18/18] ibmvfc: drop host lock when completing commands in CRQ

2020-12-04 Thread Brian King 
On 12/2/20 8:08 PM, Tyrel Datwyler wrote:
> The legacy CRQ holds the host lock the even while completing commands.
> This presents a problem when in legacy single queue mode and
> nr_hw_queues is greater than one since calling scsi_done() introduces
> the potential for deadlock.
> 
> If nr_hw_queues is greater than one drop the hostlock in the legacy CRQ
> path when completing a command.
> 
> Signed-off-by: Tyrel Datwyler 
> ---
>  drivers/scsi/ibmvscsi/ibmvfc.c | 8 +++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
> index e499599662ec..e2200bdff2be 100644
> --- a/drivers/scsi/ibmvscsi/ibmvfc.c
> +++ b/drivers/scsi/ibmvscsi/ibmvfc.c
> @@ -2969,6 +2969,7 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, 
> struct ibmvfc_host *vhost)
>  {
>   long rc;
>   struct ibmvfc_event *evt = (struct ibmvfc_event 
> *)be64_to_cpu(crq->ioba);
> + unsigned long flags;
>  
>   switch (crq->valid) {
>   case IBMVFC_CRQ_INIT_RSP:
> @@ -3039,7 +3040,12 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, 
> struct ibmvfc_host *vhost)
>   del_timer(>timer);
>   list_del(>queue);
>   ibmvfc_trc_end(evt);
> - evt->done(evt);
> + if (nr_scsi_hw_queues > 1) {
> + spin_unlock_irqrestore(vhost->host->host_lock, flags);
> + evt->done(evt);
> + spin_lock_irqsave(vhost->host->host_lock, flags);
> + } else
> + evt->done(evt);

Similar comment here as previously. The flags parameter is an output for
spin_lock_irqsave but an input for spin_unlock_irqrestore. You'll need
to rethink the locking here. You could just do a spin_unlock_irq / spin_lock_irq
here and that would probably be OK, but probably isn't the best. 

>  }
>  
>  /**
> 


-- 
Brian King
Power Linux I/O
IBM Linux Technology Center

[PATCH v3 18/18] ibmvfc: drop host lock when completing commands in CRQ

2020-12-02 Thread Tyrel Datwyler 
The legacy CRQ holds the host lock the even while completing commands.
This presents a problem when in legacy single queue mode and
nr_hw_queues is greater than one since calling scsi_done() introduces
the potential for deadlock.

If nr_hw_queues is greater than one drop the hostlock in the legacy CRQ
path when completing a command.

Signed-off-by: Tyrel Datwyler 
---
 drivers/scsi/ibmvscsi/ibmvfc.c | 8 +++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
index e499599662ec..e2200bdff2be 100644
--- a/drivers/scsi/ibmvscsi/ibmvfc.c
+++ b/drivers/scsi/ibmvscsi/ibmvfc.c
@@ -2969,6 +2969,7 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, 
struct ibmvfc_host *vhost)
 {
long rc;
struct ibmvfc_event *evt = (struct ibmvfc_event 
*)be64_to_cpu(crq->ioba);
+   unsigned long flags;
 
switch (crq->valid) {
case IBMVFC_CRQ_INIT_RSP:
@@ -3039,7 +3040,12 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, 
struct ibmvfc_host *vhost)
del_timer(>timer);
list_del(>queue);
ibmvfc_trc_end(evt);
-   evt->done(evt);
+   if (nr_scsi_hw_queues > 1) {
+   spin_unlock_irqrestore(vhost->host->host_lock, flags);
+   evt->done(evt);
+   spin_lock_irqsave(vhost->host->host_lock, flags);
+   } else
+   evt->done(evt);
 }
 
 /**
-- 
2.27.0