Re: question on freeze and aio

[Nigel Cunningham <nigel@nigel.suspend2.net>]

Hi.

On Fri, 2007-02-09 at 17:03 -0500, Alan Stern wrote:
> On Sat, 10 Feb 2007, Nigel Cunningham wrote:
> 
> > Hi.
> > 
> > On Fri, 2007-02-09 at 17:04 +0100, Oliver Neukum wrote:
> > > Hi,
> > > 
> > > can there be running aio requests if all tasks are frozen?
> > 
> > Since tasks are frozen, no new aio requests would be submitted. We do a
> > sync to ssek to complete existing requests; I haven't looked to see
> > whether that would need extending to flush aio as well, but don't think
> > that would be the case. Given everyone else's silence, so far, you might
> > be better to ask the author(s) of the aio code.
> 
> I believe Nigel is basically correct.  However sync will only flush aio 
> for block devices.  Other types of aio will remain active.
> 
> aio callbacks are interrupt-driven and execute in a workqueue (see
> fs/aio.c), and as far as I can tell that workqueue doesn't freeze.  
> Unless some general facility freezes all workqueues...

Hmm. That applies to Raid, too? I've had some reports of raid i/o being
caught in the BUG_ON() I have to catch I/O that shouldn't be happening,
but haven't gotten around to looking at them yet.

Regards,

Nigel