Re: [PATCH 00/11] Task watchers: Introduction

[Matt Helsley <matthltc@us.ibm.com>]

On Wed, 2006-06-21 at 21:41 +1000, Peter Williams wrote:
> Peter Williams wrote:
> > Matt Helsley wrote:
> >> On Wed, 2006-06-21 at 15:41 +1000, Peter Williams wrote:
> >>> On a related note, I can't see where the new task's notify field gets 
> >>> initialized during fork.
> >>
> >> It's initialized in kernel/sys.c:notify_per_task_watchers(), which calls
> >> RAW_INIT_NOTIFIER_HEAD(&task->notify) in response to WATCH_TASK_INIT.
> > 
> > I think that's too late.  It needs to be done at the start of 
> > notify_watchers() before any other watchers are called for the new task.

	I don't see why you think it's too late. It needs to be initialized
before it's used. Waiting until notify_per_task_watchers() is called
with WATCH_TASK_INIT does this.

> On second thoughts, it would simpler just before the WATCH_TASK_INIT 
> call in copy_process() in fork.c.  It can be done unconditionally there.
> 
> Peter

	That would work. It would not simplify the control flow of the code.
The branch for WATCH_TASK_INIT in notify_per_task_watchers() is
unavoidable; we need to call the parent task's chain in that case since
we know the child task's is empty.

	It is also counter to one goal of the patches -- reducing the "clutter"
in these paths. Arguably task watchers is the same kind of clutter that
existed before. However, it is a means of factoring such clutter into
fewer instances (ideally one) of the pattern.

Cheers,
	-Matt Helsley

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