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SubjectRe: [PATCH] Make e100 suspend handler support PCI cards lacking PM capability
Hi,

On Sun, Jun 14, 2009 at 07:09:45PM +0200, Rafael J. Wysocki wrote:
> On Sunday 14 June 2009, Andreas Mohr wrote:
> > - why do we call netif_device_detach() _after_ doing hardware shutdown
> > of the network controller? I'd guess this can cause huge issues?
> > Someone told me he had rtnl lock issues upon S2D with e100
> > (very similar to my rtnl issues during aborted .suspend),
> > and that might possibly be the reason?
>
> I think you're right, but I'm not a network driver expert.
>
> Perhaps you can change the ordering and see if that fixes the rtnl issue
> (since you're able to reproduce it without my patch, that should be easy to
> verify).

Well, I just moved netif_device_detach() above netif_running() check,
but this didn't fix my network issues in case of a rejecting .suspend
handler: after resume when unloading e100, that hangs, and I get tons of
rtnl timeouts and locked rtnl mutex.
This is most likely because upon e100 unload, a backtrace showed that I
was hanging in e100_down -> msleep (somewhere at the very beginning of e100_down),
which is most definitely the inlined napi_disable() call there:

static inline void napi_disable(struct napi_struct *n)
{
set_bit(NAPI_STATE_DISABLE, &n->state);
while (test_and_set_bit(NAPI_STATE_SCHED, &n->state))
msleep(1);
clear_bit(NAPI_STATE_DISABLE, &n->state);
}
IOW the .suspend seems to keep NAPI layer active, yet due to .suspend failure
there's no .resume called, thus card is in an _inoperable_ state and
NAPI cannot be processed any further, thus napi_disable() on driver unload
locks up.


BTW, in include/linux/napi.h, shouldn't napi_disable() make use of
napi_synchronize() instead of C&P?
(simply move napi_synchronize() above napi_disable() and use it there)
Oh wait, there's the CONFIG_SMP complication:
napi_synchronize() is implemented for SMP only, whereas napi_disable()
checks the same thing _always_.
(or is it a BUG that napi_disable() does the same check for non-SMP,
too??)

Thanks,

Andreas Mohr


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