Re: [RFC] [PATCH 2/2] kdump: cciss driver initialization issue fix

[Andrew Morton <akpm@osdl.org>]

On Sat, 24 Jun 2006 07:19:54 -0400
Vivek Goyal <vgoyal@in.ibm.com> wrote:

> On Fri, Jun 23, 2006 at 11:55:53PM -0700, Andrew Morton wrote:
> > On Fri, 23 Jun 2006 17:04:24 -0400
> > Vivek Goyal <vgoyal@in.ibm.com> wrote:
> > 
> > > 
> > > o cciss driver initialization fails and hits BUG() if underlying device
> > >   was active during the driver initialization. Device might be active
> > >   if previous kernel crashed and this kernel is booting after that using
> > >   kdump.
> > > 
> > >
> > > ...
> > >
> > > o If crash_boot parameter is set, then ignore the completed command messages
> > >   sent by device which have not been issued in the context of this kernel.
> > > 
> > > Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
> > > ---
> > > 
> > >  linux-2.6.17-1M-vivek/drivers/block/cciss.c |    7 +++++++
> > >  1 files changed, 7 insertions(+)
> > > 
> > > diff -puN drivers/block/cciss.c~cciss-initialization-issue-over-kdump-fix drivers/block/cciss.c
> > > --- linux-2.6.17-1M/drivers/block/cciss.c~cciss-initialization-issue-over-kdump-fix	2006-06-23 14:04:55.000000000 -0400
> > > +++ linux-2.6.17-1M-vivek/drivers/block/cciss.c	2006-06-23 14:08:12.000000000 -0400
> > > @@ -1976,6 +1976,13 @@ static int add_sendcmd_reject(__u8 cmd, 
> > >  			ctlr, complete);
> > >  		/* not much we can do. */
> > >  #ifdef CONFIG_CISS_SCSI_TAPE
> > > +		/* We might get notification of completion of commands
> > > +		 * which we never issued in this kernel if this boot is
> > > +		 * taking place after previous kernel's crash. Simply
> > > +		 * ignore the commands in this case.
> > > +		 */
> > > +		if (crash_boot)
> > > +			return 0;
> > >  		return 1;
> > 
> > Looks like this is working around a driver problem rather than fixing it
> > properly ;)
> 
> That's true. Its more of a working around the problem. I think in all
> such cases we should soft reset the device so that device drops the messages
> issued from the context of previous kernel and starts afresh.

Sounds good.

> But looks like not all the devices provide software reset facility
> (Or I can't find it out from the source code or limited documentation
> available). Mike, can I soft reset this device?
> 
> I am facing similar problem in megaraid driver as well where detailed
> technical documentation is not available and I can't find a way to
> soft reset the device.

Megaraid has a maintainer who has documents and hardware engineers.

> Or is there a generic way to handle these situations? Fixing them driver
> by driver is a long painful process. 

Some generic way of whacking a PCI device via the standard PCI registers? 
Not that I know of.