Re: [PATCH] panic.c: export panic_on_oops

Arjan van de Ven
2009-10-12T14:12:39Z

On Mon, 12 Oct 2009 13:37:58 +0200
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Artem Bityutskiy <dedekind1@gmail.com> wrote:
>
> > On Mon, 2009-10-12 at 13:15 +0200, ext Ingo Molnar wrote:
> > > > We use the mtdoops module which stores oopses on the Flash
> > > > partition, in order to make it possible to analyze them later.
> > > > And mtdoops needs to know whether 'panic_on_oops' is on or off.
> > > > Thus, we need this variable to be exported.
> > >
> > > hm, why does it need it? Could you send the patch please that
> > > makes use of it (as an easy way to explain the need for the
> > > export) - current upstream drivers/mtd/mtdoops.c doesnt need it
> > > so it must be some pending change.
> >
> > Yes, current drivers/mtd/mtdoops.c does not need it, but we have
> > this patch:
> >
> > http://lists.infradead.org/pipermail/linux-mtd/2009-October/027450.html
> >
> > which makes sure mtdoops writes the oops log immediately, because we
> > have 'panic_on_oops' set so this is our last chance to save the
> > oops.
> >
> > Here is the patch inlined as well:
> >
> > Author: Aaro Koskinen <aaro.koskinen@nokia.com>
> > Date: Thu Oct 1 18:16:55 2009 +0300
> >
> > mtd: mtdoops: do not schedule work if we are going to die
> >
> > If panic_on_oops is set, the log should be written right away
> > because this is not going to be a second chance.
> >
> > Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
> > Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
> >
> > diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> > index 1060337..ac67833 100644
> > --- a/drivers/mtd/mtdoops.c
> > +++ b/drivers/mtd/mtdoops.c
> > @@ -335,7 +335,7 @@ static void mtdoops_console_sync(void)
> > cxt->ready = 0;
> > spin_unlock_irqrestore(&cxt->writecount_lock, flags);
> >
> > - if (mtd->panic_write && in_interrupt())
> > + if (mtd->panic_write && (in_interrupt() || panic_on_oops))
> > /* Interrupt context, we're going to panic so try
> > and log */ mtdoops_write(cxt, 1);
>
> Hm, the code seems to be somewhat confused about this. It tries to
> guess when it's panic-ing, right? in_interrupt() is the wrong test
> for that.
>
> mtdoops_console_sync() gets called by regular printk() as well via:
>
> static void
> mtdoops_console_write(struct console *co, const char *s, unsigned int
> count) {
> struct mtdoops_context *cxt = co->data;
> struct mtd_info *mtd = cxt->mtd;
> unsigned long flags;
>
> if (!oops_in_progress) {
> mtdoops_console_sync();
> return;
>
> I think this is all layered incorrectly - because mtdoops (which is a
> _VERY_ cool debugging facility btw - i wish generic x86 had something
> like that) tries to be a 'driver' and tries to achieve these things
> without modifying the core kernel.
>
> But it really should do that. We can certainly enhance the core
> kernel logic to tell the console driver more clearly when printk
> should go out immediately.
>
> Instead of using oops_in_progress it might be better to go into 'sync
> immeditately' mode if the kernel gets tainted.

actually there are very nice "begin of oops" and "end of oops"
functions... they are the perfect places for this ;-)

--
Arjan van de Ven Intel Open Source Technology Centre
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