[Qemu-devel] Re: [PATCH 2/2] lsi, scsi-disk: check for reentrance via tag matching

[Ryan Harper <ryanh@us.ibm.com>]

* Anthony Liguori <anthony@codemonkey.ws> [2009-01-23 09:09]:
> 
> By virtue of the fact that we do bdrv_aio_read() here, it *has* to be 
> safe to run the scsi_command_completes from a bottom half because 
> scsi_read_complete is going to get invoked from a bottom half anyway in 
> this path.
> 
> Am I missing something?

Just moving scsi_command_complete to a bottom half won't be sufficent
since lsi_command_complete() is also re-entrent via calls to
lsi_resume_script() which can invoke lsi_do_command().  The issue of
bottom halves for lsi is something I've thought about, but haven't
figured out how to only execute enough lsi scripts to complete the
current command.  Having the device stop executing scripts after sending
back the command completion to the OS was my first though on how to
prevent this loop, but so far, just stopping after just sending
the completion back to the OS isn't something that the OS driver
handles well.

I suppose once we figure out how to stop executing scripts after
sending command completion in a way that the OS drivers understand,
moving that to a bottom half will work fine.


-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
ryanh@us.ibm.com