Re: [PATCH 1/2] mac80211: do not iterate active interfaces when in re-configure

[Adrian Chadd]

fwiw, I'm facing the same kinds of cleanup problems with my port of
(oct 2015) ath10k to freebsd.

The oct 2015 ath10k tree doesn't have the firmware per-txq/tid/peer
feedback stuff in it, so this hasn't yet bitten me, but there rest of
the races have - mostly surrounding handling pending TX frames when a
VAP is deleted (vdev/interface in ath10k/mac80211 language) and if any
TX frames were stuck. Stuck TX frames happens more often than I'd like
because of how earlier firmware required peer entries to first appear
in the hardware.

Maybe we need some kind of lifecycle checkpoint for things like peer
addition/removal (for the txq issues ben had before) and the ability
to ask the firmware to stop/flush HTT TX and re-start it. That way we
can cleanly add/remove interfaces at any point without worrying about
any dangling frames in the transmit queue waiting for completion.



-adrian

Re: [PATCH 1/2] mac80211: do not iterate active interfaces when in re-configure

[Ben Greear]

On 12/05/2016 07:00 AM, Johannes Berg wrote:

On Mon, 2016-12-05 at 06:57 -0800, Ben Greear wrote:


I think clearing sdata-in-driver would fix the ath10k problem, at
least, but I was afraid it would break something else in mac80211 or
maybe in other thick firmware drivers.


It's pretty much an internal thing - not sure what it'd break. OTOH,
some drivers might actually assume that iterating finds them all, if
they never clear the data even across a restart?


One way or another, we cannot be iterating over interfaces while
the interfaces are at the same time being (re)added.


Well, we obviously *can* be, and we do in fact do that - it's just that
ath10k specifically has issues with the data it's putting there, no?


It causes races that appear to be very difficult to resolve in the
driver alone.  On normal bringup of an interface, the sdata-in-driver
flag is only set at the bottom of the add-interface.  In case of re-config,
the flag is already set, and never cleared, so behaviour is different
w/regard to the iterate.




Maybe mac80211 should explicitly remove all interfaces from the
driver during crash recovery?


I don't think that'll work. Removing them would interact with the
firmware, which is dead, etc. That'd just cause trouble.


That issue already causes trouble and is dealt with in ath10k, I think,
but clearing the flag in mac80211 would probably be enough to fix the
iterate logic.


And the behaviour needs to be clearly documented somewhere
easy to find so that we can think about and program to the correct
API behaviour.


We assume that the driver resets all its internal state - this whole
interface iteration is a corner case we hadn't considered, I suppose.


Yeah, tricky beastie.  I think the txq issue is also part of this since there
are references up in mac80211 and also down in ath10k.  Part of my hack
to clean up that crash might be resolved by mac80211 doing better cleanup
API when firmware crashes.

Thanks,
Ben



johannes



--
Ben Greear 
Candela Technologies Inc  http://www.candelatech.com

Re: [PATCH 1/2] mac80211: do not iterate active interfaces when in re-configure

[Johannes Berg]

On Mon, 2016-12-05 at 06:57 -0800, Ben Greear wrote:

> I think clearing sdata-in-driver would fix the ath10k problem, at
> least, but I was afraid it would break something else in mac80211 or
> maybe in other thick firmware drivers.

It's pretty much an internal thing - not sure what it'd break. OTOH,
some drivers might actually assume that iterating finds them all, if
they never clear the data even across a restart?

> One way or another, we cannot be iterating over interfaces while
> the interfaces are at the same time being (re)added.

Well, we obviously *can* be, and we do in fact do that - it's just that
ath10k specifically has issues with the data it's putting there, no?

> Maybe mac80211 should explicitly remove all interfaces from the
> driver during crash recovery?  

I don't think that'll work. Removing them would interact with the
firmware, which is dead, etc. That'd just cause trouble.

> And the behaviour needs to be clearly documented somewhere
> easy to find so that we can think about and program to the correct
> API behaviour.

We assume that the driver resets all its internal state - this whole
interface iteration is a corner case we hadn't considered, I suppose.

johannes

Re: [PATCH 1/2] mac80211: do not iterate active interfaces when in re-configure

[Johannes Berg]

On Mon, 2016-12-05 at 09:13 +0100, Michal Kazior wrote:
> On 2 December 2016 at 03:29,   wrote:
> > 
> > From: Ben Greear 
> > 
> > This appears to fix a problem where ath10k firmware would crash,
> > mac80211 would start re-adding interfaces to the driver, but the
> > iterate-active-interfaces logic would then try to use the half-
> > built
> > interfaces.  With a bit of extra debug to catch the problem, the
> > ath10k crash looks like this:
> > 
> > ath10k_pci :05:00.0: Initializing arvif: 8801ce97e320 on
> > vif: 8801ce97e1d8
> > 
> > [the print that happens after arvif->ar is assigned is not shown,
> > so code did not make it that far before
> >  the tx-beacon-nowait method was called]
> > 
> > tx-beacon-nowait:  arvif: 8801ce97e320  ar:   (null)
> [...]
> > 
> > 
> > Signed-off-by: Ben Greear 
> > ---
> >  net/mac80211/util.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/net/mac80211/util.c b/net/mac80211/util.c
> > index 863f2c1..abe1f64 100644
> > --- a/net/mac80211/util.c
> > +++ b/net/mac80211/util.c
> > @@ -705,7 +705,7 @@ static void __iterate_interfaces(struct
> > ieee80211_local *local,
> > break;
> > }
> > if (!(iter_flags & IEEE80211_IFACE_ITER_RESUME_ALL)
> > &&
> > -   active_only && !(sdata->flags &
> > IEEE80211_SDATA_IN_DRIVER))
> > +   (active_only && (local->in_reconfig || !(sdata-
> > >flags & IEEE80211_SDATA_IN_DRIVER
> > continue;
> 
> Doesn't this effectivelly prevent you from iterating over interfaces
> completely during reconfig? As you bring up interfaces you might
> need/want to iterate over others to re-adjust your own state.

Agree, that doesn't really make sense.

> I'd argue there should be another flag, IEEE80211_SDATA_RESUMING,
> used with sdata->flags for resuming so that once it is re-added to
> the driver it can be cleared (and therefore properly iterated over).

That would make some sense, or perhaps the sdata_in_driver should be
cleared (and remembered elsewhere) at some point during the restart.

johannes

Re: [PATCH 1/2] mac80211: do not iterate active interfaces when in re-configure

[Michal Kazior]

On 2 December 2016 at 03:29,   wrote:
> From: Ben Greear 
>
> This appears to fix a problem where ath10k firmware would crash,
> mac80211 would start re-adding interfaces to the driver, but the
> iterate-active-interfaces logic would then try to use the half-built
> interfaces.  With a bit of extra debug to catch the problem, the
> ath10k crash looks like this:
>
> ath10k_pci :05:00.0: Initializing arvif: 8801ce97e320 on vif: 
> 8801ce97e1d8
>
> [the print that happens after arvif->ar is assigned is not shown, so code did 
> not make it that far before
>  the tx-beacon-nowait method was called]
>
> tx-beacon-nowait:  arvif: 8801ce97e320  ar:   (null)
[...]
>
> Signed-off-by: Ben Greear 
> ---
>  net/mac80211/util.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/mac80211/util.c b/net/mac80211/util.c
> index 863f2c1..abe1f64 100644
> --- a/net/mac80211/util.c
> +++ b/net/mac80211/util.c
> @@ -705,7 +705,7 @@ static void __iterate_interfaces(struct ieee80211_local 
> *local,
> break;
> }
> if (!(iter_flags & IEEE80211_IFACE_ITER_RESUME_ALL) &&
> -   active_only && !(sdata->flags & 
> IEEE80211_SDATA_IN_DRIVER))
> +   (active_only && (local->in_reconfig || !(sdata->flags & 
> IEEE80211_SDATA_IN_DRIVER
> continue;

Doesn't this effectivelly prevent you from iterating over interfaces
completely during reconfig? As you bring up interfaces you might
need/want to iterate over others to re-adjust your own state.

I'd argue there should be another flag, IEEE80211_SDATA_RESUMING, used
with sdata->flags for resuming so that once it is re-added to the
driver it can be cleared (and therefore properly iterated over).


Michał