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    SubjectRe: [PATCH 3.6-rc6] cpufreq/powernow-k8: workqueue user shouldn't migrate the kworker to another CPU
    So, with work_on_cpu() reimplementation just posted[1], we can do the
    following instead. Functionally it's about the same but less ugly.
    Ugly as it may be, I think the previous open coded version is better
    suited as a fix and for -stable. Thoughts?

    Thanks.

    [1] https://lkml.org/lkml/2012/9/18/430

    drivers/cpufreq/powernow-k8.c | 63 ++++++++++++++++++++++--------------------
    1 file changed, 34 insertions(+), 29 deletions(-)

    diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
    index c0e8164..1a40935 100644
    --- a/drivers/cpufreq/powernow-k8.c
    +++ b/drivers/cpufreq/powernow-k8.c
    @@ -35,7 +35,6 @@
    #include <linux/slab.h>
    #include <linux/string.h>
    #include <linux/cpumask.h>
    -#include <linux/sched.h> /* for current / set_cpus_allowed() */
    #include <linux/io.h>
    #include <linux/delay.h>

    @@ -1139,16 +1138,23 @@ static int transition_frequency_pstate(struct powernow_k8_data *data,
    return res;
    }

    -/* Driver entry point to switch to the target frequency */
    -static int powernowk8_target(struct cpufreq_policy *pol,
    - unsigned targfreq, unsigned relation)
    +struct powernowk8_target_arg {
    + struct cpufreq_policy *pol;
    + unsigned targfreq;
    + unsigned relation;
    +};
    +
    +static long powernowk8_target_fn(void *arg)
    {
    - cpumask_var_t oldmask;
    + struct powernowk8_target_arg *pta = arg;
    + struct cpufreq_policy *pol = pta->pol;
    + unsigned targfreq = pta->targfreq;
    + unsigned relation = pta->relation;
    struct powernow_k8_data *data = per_cpu(powernow_data, pol->cpu);
    u32 checkfid;
    u32 checkvid;
    unsigned int newstate;
    - int ret = -EIO;
    + int ret;

    if (!data)
    return -EINVAL;
    @@ -1156,29 +1162,16 @@ static int powernowk8_target(struct cpufreq_policy *pol,
    checkfid = data->currfid;
    checkvid = data->currvid;

    - /* only run on specific CPU from here on. */
    - /* This is poor form: use a workqueue or smp_call_function_single */
    - if (!alloc_cpumask_var(&oldmask, GFP_KERNEL))
    - return -ENOMEM;
    -
    - cpumask_copy(oldmask, tsk_cpus_allowed(current));
    - set_cpus_allowed_ptr(current, cpumask_of(pol->cpu));
    -
    - if (smp_processor_id() != pol->cpu) {
    - printk(KERN_ERR PFX "limiting to cpu %u failed\n", pol->cpu);
    - goto err_out;
    - }
    -
    if (pending_bit_stuck()) {
    printk(KERN_ERR PFX "failing targ, change pending bit set\n");
    - goto err_out;
    + return -EIO;
    }

    pr_debug("targ: cpu %d, %d kHz, min %d, max %d, relation %d\n",
    pol->cpu, targfreq, pol->min, pol->max, relation);

    if (query_current_values_with_pending_wait(data))
    - goto err_out;
    + return -EIO;

    if (cpu_family != CPU_HW_PSTATE) {
    pr_debug("targ: curr fid 0x%x, vid 0x%x\n",
    @@ -1196,7 +1189,7 @@ static int powernowk8_target(struct cpufreq_policy *pol,

    if (cpufreq_frequency_table_target(pol, data->powernow_table,
    targfreq, relation, &newstate))
    - goto err_out;
    + return -EIO;

    mutex_lock(&fidvid_mutex);

    @@ -1209,9 +1202,8 @@ static int powernowk8_target(struct cpufreq_policy *pol,
    ret = transition_frequency_fidvid(data, newstate);
    if (ret) {
    printk(KERN_ERR PFX "transition frequency failed\n");
    - ret = 1;
    mutex_unlock(&fidvid_mutex);
    - goto err_out;
    + return 1;
    }
    mutex_unlock(&fidvid_mutex);

    @@ -1220,12 +1212,25 @@ static int powernowk8_target(struct cpufreq_policy *pol,
    data->powernow_table[newstate].index);
    else
    pol->cur = find_khz_freq_from_fid(data->currfid);
    - ret = 0;

    -err_out:
    - set_cpus_allowed_ptr(current, oldmask);
    - free_cpumask_var(oldmask);
    - return ret;
    + return 0;
    +}
    +
    +/* Driver entry point to switch to the target frequency */
    +static int powernowk8_target(struct cpufreq_policy *pol,
    + unsigned targfreq, unsigned relation)
    +{
    + struct powernowk8_target_arg pta = { .pol = pol, .targfreq = targfreq,
    + .relation = relation };
    +
    + /*
    + * Must run on @pol->cpu. cpufreq core is responsible for ensuring
    + * that we're bound to the current CPU and pol->cpu stays online.
    + */
    + if (smp_processor_id() == pol->cpu)
    + return powernowk8_target_fn(&pta);
    + else
    + return work_on_cpu(pol->cpu, powernowk8_target_fn, &pta);
    }

    /* Driver entry point to verify the policy and range of frequencies */

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