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    SubjectRe: [PATCH RFC] pm_qos_requirement might sleep
    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:
    > > Even after applying some fixes posted by Chirag and Peter Z, I'm still
    > > getting some messages in my log like this
    >
    > > 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 ]
    >
    > > 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);
    > >


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