netdev - Re: [PATCH 1/2] Convert target drivers to use sbitmap

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Date:   Tue, 12 Jun 2018 16:32:03 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "willy@...radead.org" <willy@...radead.org>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kent.overstreet@...il.com" <kent.overstreet@...il.com>,
        "linux1394-devel@...ts.sourceforge.net" 
        <linux1394-devel@...ts.sourceforge.net>,
        "jgross@...e.com" <jgross@...e.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "mawilcox@...rosoft.com" <mawilcox@...rosoft.com>,
        "qla2xxx-upstream@...gic.com" <qla2xxx-upstream@...gic.com>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/2] Convert target drivers to use sbitmap

On Tue, 2018-06-12 at 09:15 -0700, Matthew Wilcox wrote:
> On Tue, Jun 12, 2018 at 03:22:42PM +0000, Bart Van Assche wrote:
> > On Tue, 2018-05-15 at 09:00 -0700, Matthew Wilcox wrote:
> > > diff --git a/drivers/scsi/qla2xxx/qla_target.c b/drivers/scsi/qla2xxx/qla_target.c
> > > index 025dc2d3f3de..cdf671c2af61 100644
> > > --- a/drivers/scsi/qla2xxx/qla_target.c
> > > +++ b/drivers/scsi/qla2xxx/qla_target.c
> > > @@ -3719,7 +3719,8 @@ void qlt_free_cmd(struct qla_tgt_cmd *cmd)
> > >  		return;
> > >  	}
> > >  	cmd->jiffies_at_free = get_jiffies_64();
> > > -	percpu_ida_free(&sess->se_sess->sess_tag_pool, cmd->se_cmd.map_tag);
> > > +	sbitmap_queue_clear(&sess->se_sess->sess_tag_pool, cmd->se_cmd.map_tag,
> > > +			cmd->se_cmd.map_cpu);
> > >  }
> > >  EXPORT_SYMBOL(qlt_free_cmd);
> > 
> > Please introduce functions in the target core for allocating and freeing a tag
> > instead of spreading the knowledge of how to allocate and free tags over all
> > target drivers.
> 
> I can't without doing an unreasonably large amount of work on drivers that
> I have no way to test.  Some of the drivers have the se_cmd already; some
> of them don't.  I'd be happy to introduce a common function for freeing
> a tag.

Which target drivers are you referring to? If you are referring to the sbp driver:
I think that driver is dead and can be removed from the kernel tree. I even don't
know whether that driver ever has had any users other than the developer of that
driver.

> > This looks weird to me. Shouldn't target code ignore signals instead of causing
> > tag allocation to fail if a signal is received?
> 
> It's what the current code did:
> 
> -               if (signal_pending_state(state, current)) {
> -                       tag = -ERESTARTSYS;
> -                       break;
> -               }
> 
> and the current callers literally indicate that they want signals:
> 
> drivers/infiniband/ulp/isert/ib_isert.c:        cmd = iscsit_allocate_cmd(conn, TASK_INTERRUPTIBLE);
> drivers/target/iscsi/iscsi_target.c:    cmd = iscsit_allocate_cmd(conn, TASK_INTERRUPTIBLE);

Right, the iSCSI target driver uses signals to wake up threads (see also the
send_sig() calls in the iSCSI target code).

Bart.