Ryan Harper wrote:
* Anthony Liguori <anthony@xxxxxxxxxxxxx> [2009-01-23 09:09]:
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.
I think we're talking past each other. Let me describe what my
(limited) understanding of the problem is and you can correct me if I've
got it wrong.
lsi_do_command():
does some action on the next command
stores some info in global state
calls into scsi disk
scsi_disk normally does:
bdrv_aio_read() with callback of scsi_complete.
returns
lsi_do_command()
finishes up command and touching global state
returns
When IO completes:
scsi_complete:
executes lsi_do_command() to run next command
We run into trouble when:
lsi_do_command():
does some action on the next command
stores some info in global state
calls into scsi disk
scsi_disk abnormally does:
scsi_command_complete()
scsi_command_complete:
executes lsi_do_command() to run next command
lsi_do_command():
does some action on the next command
we're fubar because the global state is setup to process another command
So what a bottom half would do is:
lsi_do_command():
does some action on the next command
stores some info in global state
calls into scsi disk
scsi_disk abnormally does:
schedule bottom half for scsi_command_complete
returns
lsi_do_command()
finishes up command and touching global state
returns
When bottom halves get run
scsi_complete:
executes lsi_do_command() to run next command
And we avoid getting fubar.
Regards,
Anthony Liguori
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