On Tue, Aug 05, 2008 at 09:25:01AM +0200, Peter Zijlstra wrote:

On Mon, 2008-08-04 at 22:52 +0200, John Kacur wrote:

quoted

Even after applying some fixes posted by Chirag and Peter Z, I'm still
getting some messages in my log like this

quoted

BUG: sleeping function called from invalid context swapper(0) at
kernel/rtmutex.c:743
in_atomic():1 [00000001], irqs_disabled():1
Pid: 0, comm: swapper Tainted: G        W 2.6.26.1-rt1.jk #2

Call Trace:
 [<ffffffff802305d3>] __might_sleep+0x12d/0x132
 [<ffffffff8046cdbe>] __rt_spin_lock+0x34/0x7d
 [<ffffffff8046ce15>] rt_spin_lock+0xe/0x10
 [<ffffffff802532e5>] pm_qos_requirement+0x1f/0x3c
 [<ffffffff803e1b7f>] menu_select+0x7b/0x9c
 [<ffffffff8020b1be>] ? default_idle+0x0/0x5a
 [<ffffffff8020b1be>] ? default_idle+0x0/0x5a
 [<ffffffff803e0b4b>] cpuidle_idle_call+0x68/0xd8
 [<ffffffff803e0ae3>] ? cpuidle_idle_call+0x0/0xd8
 [<ffffffff8020b1be>] ? default_idle+0x0/0x5a
 [<ffffffff8020b333>] cpu_idle+0xb2/0x12d
 [<ffffffff80466af0>] start_secondary+0x186/0x18b

---------------------------
| preempt count: 00000001 ]
| 1-level deep critical section nesting:
----------------------------------------
... [<ffffffff8020b39c>] .... cpu_idle+0x11b/0x12d
......[<ffffffff80466af0>] ..   ( <= start_secondary+0x186/0x18b)

The following simple patch makes the messages disappear - however,
there may be a better more fine grained solution, but the problem is
also that all the functions are designed to use the same lock.

Hmm, I think you're right - its called from the idle routine so we can't
go about sleeping there.

The only trouble I have is with kernel/pm_qos_params.c:update_target()'s
use of this lock - that is decidedly not O(1).

Mark, would it be possible to split that lock in two, one lock
protecting pm_qos_array[], and one lock protecting the
requirements.list ?

very likely, but I'm not sure how it will help.

the fine grain locking I had initially worked out on pm_qos was to have
a lock per pm_qos_object, that would be used for accessing the
requirement_list and the target_value.  But that isn't what you are
asking about is it?

Is what you want is a pm_qos_requirements_list_lock and a
pm_qos_target_value_lock, for each pm_qos_object instance?

I guess it wold work but besides giving the code spinlock diarrhea would
it really help solve the issue you are seeing? 

--mgross

 

[ NOTE: this is the -rt kernel we're talking about ]

quoted

Signed-off-by: John Kacur <jkacur at gmail dot com>

Index: linux-2.6.26.1-jk-rt1/kernel/pm_qos_params.c
===================================================================

--- linux-2.6.26.1-jk-rt1.orig/kernel/pm_qos_params.c
+++ linux-2.6.26.1-jk-rt1/kernel/pm_qos_params.c

@@ -110,7 +110,7 @@ static struct pm_qos_object *pm_qos_arra
        &network_throughput_pm_qos
 };
 
-static DEFINE_SPINLOCK(pm_qos_lock);
+static DEFINE_RAW_SPINLOCK(pm_qos_lock);
 
 static ssize_t pm_qos_power_write(struct file *filp, const char

__user *buf,
                size_t count, loff_t *f_pos);