Re: [PATCH] scsi, mptsas : drop scsi_host lock when calling mptsas_qcmd

["Nicholas A. Bellinger" <nab@linux-iscsi.org>]

On Thu, 2010-09-16 at 19:25 -0400, Christoph Hellwig wrote:
> On Thu, Sep 16, 2010 at 05:24:47PM -0400, James Bottomley wrote:
> > > into the drivers (similar to how it has been done with the BKL).
> > > This would be a fairly mechanic mindless patch. Lots of typing,
> > > but not really a lot of real code review needed.
> > > 
> > > Then next step the drivers who know they don't want it can remove it.
> > 
> > Yes, that's basically what Christoph did when he moved the lock out of
> > the eh path.
> 
> And it is what we should do here as well.  I'm just wondering if we rely
> on the fact that we hold the lock over the check for the device beeing
> deleted and the queuecommand call.
> 

Ugh, I completely forgot the about the (host->shost_state == SHOST_DEL)
check in scsi_dispatch_cmd() in patch #1, and just fixed this in
lio-core-2.6.git/drop-host_lock here:

http://git.kernel.org/?p=linux/kernel/git/nab/lio-core-2.6.git;a=commitdiff;h=e222907d9baac56425f87c602acdd757dc5fde08

Here is what the updated scsi_dispatch_cmd() now looks like:

	<SNIP>

        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
         */
        scsi_cmd_get_serial(host, cmd);

        if (unlikely(host->shost_state == SHOST_DEL)) {
                spin_unlock_irqrestore(host->host_lock, flags);
                cmd->result = (DID_NO_CONNECT << 16);
                scsi_done(cmd);
        } else {
                spin_unlock_irqrestore(host->host_lock, flags);
                trace_scsi_dispatch_cmd_start(cmd);
                rtn = host->hostt->queuecommand(cmd, scsi_done);
        }

	<SNIP>

Thanks!

--nab