Commit 6889125b authored by Tejun Heo's avatar Tejun Heo

cpufreq/powernow-k8: workqueue user shouldn't migrate the kworker to another CPU

powernowk8_target() runs off a per-cpu work item and if the
cpufreq_policy->cpu is different from the current one, it migrates the
kworker to the target CPU by manipulating current->cpus_allowed.  The
function migrates the kworker back to the original CPU but this is
still broken.  Workqueue concurrency management requires the kworkers
to stay on the same CPU and powernowk8_target() ends up triggerring
BUG_ON(rq != this_rq()) in try_to_wake_up_local() if it contends on
fidvid_mutex and sleeps.

It is unclear why this bug is being reported now.  Duncan says it
appeared to be a regression of 3.6-rc1 and couldn't reproduce it on
3.5.  Bisection seemed to point to 63d95a91 "workqueue: use @pool
instead of @gcwq or @cpu where applicable" which is an non-functional
change.  Given that the reproduce case sometimes took upto days to
trigger, it's easy to be misled while bisecting.  Maybe something made
contention on fidvid_mutex more likely?  I don't know.

This patch fixes the bug by using work_on_cpu() instead if @pol->cpu
isn't the same as the current one.  The code assumes that
cpufreq_policy->cpu is kept online by the caller, which Rafael tells
me is the case.

stable: ed48ece2 ("workqueue: reimplement work_on_cpu() using
        system_wq") should be applied before this; otherwise, the
        behavior could be horrible.
Signed-off-by: default avatarTejun Heo <>
Reported-by: default avatarDuncan <>
Tested-by: default avatarDuncan <>
Cc: Rafael J. Wysocki <>
Cc: Andreas Herrmann <>
parent ed48ece2
......@@ -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;
......@@ -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;
goto err_out;
return 1;
......@@ -1220,12 +1212,25 @@ static int powernowk8_target(struct cpufreq_policy *pol,
pol->cur = find_khz_freq_from_fid(data->currfid);
ret = 0;
set_cpus_allowed_ptr(current, 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);
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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