Re: [Fwd: Re: via-pmu runs device_power_down in atomic context]

[Andrew Morton <akpm@osdl.org>]

Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:
>
> -------- Forwarded Message --------
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> To: Johannes Berg <johannes@sipsolutions.net>
> Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>, Michael Hanselmann
> <linux-kernel@hansmi.ch>, cpufreq@lists.linux.org.uk
> Subject: Re: via-pmu runs device_power_down in atomic context
> Date: Thu, 25 May 2006 12:28:15 +1000
> 
> On Wed, 2006-05-24 at 10:01 +0200, Johannes Berg wrote:
> > Hey,
> > 
> > Everytime I suspend my powerbook, I see the following trace:
> > 
> > [10655.887546] BUG: sleeping function called from invalid context at include/linux/rwsem.h:43
> > [10655.887558] in_atomic():0, irqs_disabled():1
> > [10655.887562] Call Trace:
> > [10655.887565] [C581BD20] [C00081E8] show_stack+0x50/0x190 (unreliable)
> > [10655.887582] [C581BD50] [C0023BB0] __might_sleep+0xcc/0xe8
> > [10655.887592] [C581BD60] [C0038290] blocking_notifier_call_chain+0x2c/0xc0
> > [10655.887606] [C581BD80] [C01E90C0] cpufreq_suspend+0x130/0x148
> > [10655.887616] [C581BDB0] [C019D9E8] sysdev_suspend+0x10c/0x300
> > [10655.887627] [C581BDF0] [C01A3888] device_power_down+0x74/0xac
> > [10655.887636] [C581BE10] [C01B1264] pmac_suspend_devices+0x98/0x188
> > [10655.887643] [C581BE30] [C01B18F0] pmu_ioctl+0x59c/0xbc0
> > [10655.887649] [C581BED0] [C008E898] do_ioctl+0x80/0x84
> > [10655.887660] [C581BEE0] [C008E928] vfs_ioctl+0x8c/0x48c
> > [10655.887666] [C581BF10] [C008ED68] sys_ioctl+0x40/0x74
> > [10655.887673] [C581BF40] [C000F3A4] ret_from_syscall+0x0/0x38
> > 
> > The might_sleep() comes from down_read() and this happens because
> > blocking_notifier_call_chain calls it, it is also commented to run in
> > process context so this is all proper.
> 
> device_power_down should be called with interrupts off, thus the PMU
> driver is fine. It's a misnamed function, it calls the sysdev's suspend
> and those should be called with irq off. I think the problem is more due
> to some cpufreq or notifier change that somebody done to recent kernels
> and that added some might_sleep.... I wonder why. 
> 
> Andrew, what's up there ? What is this new
> "blocking_notifier_call_chain" thing ? notifiers use to not use
> semaphores and not be blocking... at least powermac implementation of
> cpufreq relies on that.

notifiers used to be racy too - we just waddled across them without any
locking.

Alan made a best-effort conversion of callers, and there have been a few
problems.

Here, pmac has gone and unilaterally decided that device_power_down() is
atomic, even though device_power_down() _already_ calls suspend_device(),
which does down().  So I'd say you've gone and found a via-pmu bug here.

A way of shutting up the warning would be to use an atomic notifier, but
it'll still be buggy.  Better would be to teach pmac_suspend_devices() not
to assume things which aren't true ;)