Re: [PATCH] Save command pool address of Scsi_Host

[Christoph Hellwig <hch@infradead.org>]

On Sat, Aug 02, 2014 at 12:24:34AM +0400, James Bottomley wrote:
> Wait, that's not right at all.  There looks to be a thinko in the
> command pool handling code.  We have both a cmd_pool in the host
> structure and in the host template structure, but there's confusion
> about which one we're supposed to be using.

For anything in the I/O path: shost->cmd_pool, for finding a pool
created for a specific host template: template->cmd_pool.

> The origin of confusion seems to be the reference counting in the pool
> itself ... you want the same pool for all hosts, since they can only
> have one cmd_size, but you want it created on first host use and
> destroyed again on the last one.
> 
> If you take this patch, a host that attached, detaches and then attaches
> a host will panic because it will use a freed pool structure.

Yes, it also needs to set hostt->cmd_pool to NULL when the last
reference goes away.