2020-12-03 02:12:59

by Tyrel Datwyler

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

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 <[email protected]>
---
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(&evt->timer);
list_del(&evt->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

2020-12-04 21:39:30

by Brian King

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

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 <[email protected]>
> ---
> 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(&evt->timer);
> list_del(&evt->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

2020-12-05 00:25:40

by Tyrel Datwyler

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

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 <[email protected]>
>> ---
>> 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(&evt->timer);
>> list_del(&evt->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

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