On Fri, Sep 24, 2010 at 01:44:00PM -0700, Nicholas A. Bellinger wrote:
> On Fri, 2010-09-24 at 08:41 -0500, Brian King wrote:
> > On 09/23/2010 06:37 PM, Nicholas A. Bellinger wrote:
> > > @@ -651,7 +655,6 @@ static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd
> > > int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
> > > {
> > > struct Scsi_Host *host = cmd->device->host;
> > > - unsigned long flags = 0;
> > > unsigned long timeout;
> > > int rtn = 0;
> > >
> > > @@ -736,15 +739,11 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
> > > scsi_done(cmd);
> > > goto out;
> > > }
> > > -
> > > - spin_lock_irqsave(host->host_lock, flags);
> > > /*
> > > - * AK: unlikely race here: for some reason the timer could
> > > - * expire before the serial number is set up below.
> > > - *
> > > - * TODO: kill serial or move to blk layer
> > > + * Note that scsi_cmd_get_serial() used to be called here, but
> > > + * now we expect the legacy SCSI LLDs that actually need this
> > > + * to call it directly within their SHT->queuecommand() caller.
> > > */
> > > - scsi_cmd_get_serial(host, cmd);
> > >
> > > if (unlikely(host->shost_state == SHOST_DEL)) {
> > > cmd->result = (DID_NO_CONNECT << 16);
> > > @@ -753,7 +752,7 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
> > > trace_scsi_dispatch_cmd_start(cmd);
> > > rtn = host->hostt->queuecommand(cmd, scsi_done);
> > > }
> > > - spin_unlock_irqrestore(host->host_lock, flags);
> > > +
> > > if (rtn) {
> > > trace_scsi_dispatch_cmd_error(cmd, rtn);
> > > if (rtn != SCSI_MLQUEUE_DEVICE_BUSY &&
> >
> > Are you planning a future revision that moves the acquiring of the host lock
> > into the LLDD's queuecommand for all the other drivers you don't currently
> > touch in this patch set?
> >
>
> Hi Brian,
>
> I was under the impression that this would be unnecessary for the vast
> majority of existing LLD drivers, but if you are aware of specific LLDs
> that would still need the struct Scsi_Host->host_lock held in their
> SHT->queuecommand() for whaterver reason please let me know and I would
> be happy to include this into an RFCv4.
>
> Thanks for your comments!
zfcp relies on having the interrupts disabled when calling
queuecommand. Without the spin_lock_irqsave in scsi_dispatch_cmd, the
locking in zfcp_fsf_send_fcp_command_task has to be changed from
spin_lock(&qdio->req_q_lock) to spin_lock_irqsave. It is a simple
change, but other drivers might have similar requirements.
Christof
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