On Tue, 2010-12-14 at 10:53 +0100, Tejun Heo wrote:
> Hello, James.
>
> On 12/12/2010 11:48 PM, James Bottomley wrote:
> > The analysis above isn't quite correct, I'm afraid. We use the
> > execute_in_process_context() not to avoid deadlocks, but to acquire
> > process context if we don't have it because the API allows calling from
> > sites at interrupt context. The point of using
> > execute_in_process_context() is that we actually want to make use of the
> > user context if we have one ... there's no point using a workqueue in
> > that case, because there's nothing to be gained (except to slow
> > everything down). We have no ordering constraints (the traditional
> > reason for using workqueues) so this is purely about context.
>
> Sure, what I tried to say was that the change couldn't introduce
> deadlock no matter how it was used. Sure execute_in_process_context()
> would be slightly more efficient, but it currently is used a few times
> only in quite cold paths where optimization isn't necessary at all and
> the API is somewhat incomplete in that it doesn't provide ordering or
> synchronization APIs.
That's the point ... it's purely for operations which require user
context which may not have it. There's no synchronisation by design
(it's a simple API).
> So, unless there's a compelling reason, let's remove it.
The open coding of if (in_atomic()) { do workqueue stuff } else
{ execute function } is rather bug prone (most people tend to do
in_interrupt()). It's better to encapsulate it in an API.
> It has been
> there for quite some time now and hasn't grown any other users. There
> wouldn't be any noticeable difference for the current users either.
> If you really like to keep it in the current users, let's move it into
> SCSI. I don't see much reason to keep it as a part of generic
> workqueue API in its current form.
It was in SCSI ... I got told to make it generic.
James
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