On Sun, Sep 02, 2012 at 11:24:47PM -0700, Gregoire Gentil wrote:

Hello,

I'm trying to debug a wifi bug with 3.4-rt17 applied, running on an
OMAP4 ARM board such as Pandaboard.

Wi-Fi works perfectly well without rt patches. It also works quite
well with rt patches AND without wifi module loaded. But with both
rt patches and wifi module, the system is very flaky and even if I
manage to launch a big download, I get a kernel hang. I managed to
get a trace:

BUG: scheduling while atomic: irq/213-wl12xx/1588/0x00010002
Modules linked in: omapdce(C) wl12xx wlcore omaprpc(C) mac80211 d
[<c001beb4>] (unwind_backtrace+0x0/0xf0) from [<c0613548>] (dump)
[<c0613548>] (dump_stack+0x20/0x24) from [<c0073908>] (__schedul)
[<c0073908>] (__schedule_bug+0x54/0x60) from [<c0614818>] (__sch)
[<c0614818>] (__schedule+0x74/0x6c0) from [<c0614f60>] (schedule)
[<c0614f60>] (schedule+0xa0/0xb8) from [<c0615eb8>] (rt_spin_loc)
[<c0615eb8>] (rt_spin_lock_slowlock+0x198/0x288) from [<c06160a8)
[<c06160a8>] (rt_spin_lock+0x18/0x1c) from [<bf0c6b24>] (wl12xx_)
[<bf0c6b24>] (wl12xx_hardirq+0x2c/0xa4 [wlcore]) from [<c00bd4f0)
[<c00bd4f0>] (handle_irq_event_percpu+0xac/0x24c) from [<c00bd70)
[<c00bd70c>] (handle_irq_event+0x7c/0x9c) from [<c00c08f0>] (han)
[<c00c08f0>] (handle_level_irq+0xe4/0x134) from [<c00bcf58>] (ge)
[<c00bcf58>] (generic_handle_irq+0x34/0x3c) from [<c03217e8>] (g)
[<c03217e8>] (gpio_irq_handler+0x160/0x1a4) from [<c00bcf58>] (g)
[<c00bcf58>] (generic_handle_irq+0x34/0x3c) from [<c001449c>] (h)
[<c001449c>] (handle_IRQ+0x88/0xc8)

Source code including the function wl12xx_hardirq is here:
http://dev.omapzoom.org/?p=integration/kernel-ubuntu.git;a=blob;f=drivers/net/wireless/ti/wlcore/main.c;h=45fe911a6504f92dddff5a9415bb77a643b3c4a9;hb=f84c72f6b36418ff11d16808c16a7c3216730bb0

Any idea what could be wrong and how I could debug and fix this situation?

On first glance, it looks like the driver uses request_threaded_irq(),
to register its handlers, but is trying to acquire a regular spin_lock
in its primary handler.  That's bad news, since spin_locks' can
schedule() when contended with CONFIG_PREEMPT_RT.

And it's not just that, unfortunately, since the primary handler also
complete()s a completion, which also can schedule().

It looks like the overall interrupt handling strategy of this driver
probably needs to be revisited. :(.

-- 
          joshc