Re: [RFC][PATCH] allow sleep inside EH hooks

[Christoph Hellwig <hch@infradead.org>]

On Fri, May 27, 2005 at 01:04:49PM -0400, James Bottomley wrote:
> On Fri, 2005-05-27 at 12:49 -0400, Jeff Garzik wrote:
> > I'm also curious to see what others think about removing the host_lock 
> > acquisition from ->queuecommand() calls.
> 
> Personally I don't see the need for it for two reasons:
> 
> 1) There are certain atomic ops in the mid layer issue that necessitate
> we acquire it anyway (serial number generation and state model checking)
> 2) All queuecommand routines should move to the model of either issuing
> or rejecting the command ... if they do that, often there's no need for
> the mucking with lock, they remain locked throughout.
> 
> On point 2), look at the changes to the aic7xxx driver.  Once its
> internal issue queueing was pulled out, it no longer needs to muck with
> the host lock in ahc_linux_queue.  If you don't enter this locked, it
> would just have to take it at the top and release it before return, as
> would most other well written drivers.

The only think host_lock in ->queuecommand protects against is the
interrupt handler, which is completely in the driver.  At which point
it makes lots of sense to use a driver-private lock for it.  Even better
we can get the scsi subsystem out of the irq disabling business once
all drivers use their own locks in the interrupt handler.