Re: spinlock in completion_done() (was: Re: Async resume patch (was: Re: [GIT PULL] PM updates for 2.6.33))

Ingo Molnar
2009-12-09T09:30:19Z

* Rafael J. Wysocki <rjw@sisk.pl> wrote:

> On Tuesday 08 December 2009, Alan Stern wrote:
> > On Tue, 8 Dec 2009, Rafael J. Wysocki wrote:
> >
> > > BTW, is there a good reason why completion_done() doesn't use spin_lock_irqsave
> > > and spin_unlock_irqrestore? complete() and complete_all() use them, so why not
> > > here?
> >
> > And likewise in try_wait_for_completion(). It looks like a bug. Maybe
> > these routines were not intended to be called with interrupts disabled,
> > but that requirement doesn't seem to be documented. And it isn't a
> > natural requirement anyway.
>
> OK, let's ask Ingo about that.
>
> Ingo, is there any particular reason why completion_done() and
> try_wait_for_completion() don't use spin_lock_irqsave() and
> spin_unlock_irqrestore()?

that's a bug that should be fixed - all the wakeup side (and atomic)
variants of completetion API should be irq safe.

It appears that these new completion APIs were added via the XFS tree
about a year ago:

39d2f1a: [XFS] extend completions to provide XFS object flush requirements

Please Cc: scheduler folks to all scheduler patches.

Ingo