Re: [PATCH] scsi_allocate_request() reference

[Jens Axboe <axboe@suse.de>]

On Tue, Mar 22 2005, Tejun Heo wrote:
>  Hello, Jens.
>  Hello, James.
> 
> On Mon, Mar 21, 2005 at 05:57:52PM +0100, Jens Axboe wrote:
> > On Mon, Mar 21 2005, James Bottomley wrote:
> > > On Mon, 2005-03-21 at 14:26 +0100, Jens Axboe wrote:
> > > > scsi_allocate_request() doesn't hold a reference to the device that it
> > > > points to, that is not good. This patch fixes that up.
> > > 
> > > Actually, I don't think this is correct.  The reference is taken when
> > > the command is attached to a request in the scsi_request_fn function
> > > after first checking that the entity is in a condition to have this
> > > happen.
> > 
> > Where does this happen, specifically? I can verify that this patch
> > solves at least one of the oopses I am seeing with hotplug. IMHO, the
> > reference should be taken when you reference the device (ie ->sr_device
> > is assigned in scsi_allocate_request()).
> 
>  I've been working on scsi hot plug/unplugging for a few days now but
> I haven't seen any oops caused by reference count problems.  The only

You need to have io in progress. The one ref problem with
scsi_allocate_request() is easy to trigger, if you just open/close the
device repeatedly while inserting and removing it.

>  So, please let me know about the reference counting problem you're
> encountering.  I will incorporate it in the new state machine /
> flushing patches.

See my two recent postings on this list!

-- 
Jens Axboe