Re: [PATCH -rt] scheduling while atomic in fs/file.c

[Steven Rostedt <rostedt@goodmis.org>]

On Sun, 14 May 2006, Daniel Walker wrote:

> On Sun, 2006-05-14 at 12:44 -0400, Steven Rostedt wrote:
> > On Sun, 14 May 2006, Daniel Walker wrote:
> >
> > > Quite the smp_processor_id() wanrings. I don't see any SMP
> > > concerns here . It just adds to a percpu list, so it shouldn't
> > > matter if it switches after sampling fdtable_defer_list .
> >
> > I'm not so sure that there isn't SMP concerns here. I have to catch a
> > train in a few minutes, otherwise I would look deeper into this. But this
> > might be a candidate to turn fdtable_defer_list into a per_cpu_locked.
>
> I reviewed it again, and it looks like these percpu structures have a
> spinlock to protect the list from being emptied by a work queue while
> things are being added to the list . The lock appears to be used
> properly .  The work queue frees struct fdtable pointers added to the
> list , the only place these structures are added is in the block I've
> modified .
>
> I think making this a locked percpu would just be overkill ..
>

It seems that the timer is percpu. So it has a timer for each cpu.  If you
switch CPUs after the put, the modtimer might put the fddef->timer onto
another CPU, and thus have more than one going off on the same CPU.

-- Steve

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