Deadlock in sd_open/revalidate [lk <= 2.4]

["Philip R. Auld" <pauld@egenera.com>]

Hi folks,
	There seems to be a potential deadlock in the sd_open path. The problem
is this while loop:

	...
	while (rscsi_disks[target].device->busy) {
                barrier();
                cpu_relax();
        }
	...

In revalidate_scsidisk we do this:
	
	...
	device->busy = 1;
	...
	almost certain schedule();
	...
	device-busy = 0;

Both paths hold the kernel lock so if sd_open gets into the while loop when 
the revalidate is sleeping it's all over.

As a simple preventative fix I'd say put a schedule in the while loop. It's
a little ugly, but less intrusive that adding a wait queue to the device.

Anoyone see anything wrong with doing that? Other solutions?

This seems to be present in 2.0, 2.2. and 2.4 (where we hit it).
The while-forever-loop-with -kernel-lock seems to be gone in 2.5.


Cheers,

Phil

-- 
Philip R. Auld, Ph.D.                  Technical Staff 
Egenera Corp.                        pauld@egenera.com
165 Forest St., Marlboro, MA 01752       (508)858-2600