path: root/drivers/cpufreq/powernow-k8.c
diff options
authorTejun Heo <tj@kernel.org>2012-09-18 14:24:59 -0700
committerTejun Heo <tj@kernel.org>2012-09-19 10:15:01 -0700
commit6889125b8b4e09c5e53e6ecab3433bed1ce198c9 (patch)
treef7408140458c2d287014fb66d2b474af01ae9658 /drivers/cpufreq/powernow-k8.c
parented48ece27cd3d5ee0354c32bbaec0f3e1d4715c3 (diff)
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: ed48ece27c ("workqueue: reimplement work_on_cpu() using system_wq") should be applied before this; otherwise, the behavior could be horrible. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Duncan <1i5t5.duncan@cox.net> Tested-by: Duncan <1i5t5.duncan@cox.net> Cc: Rafael J. Wysocki <rjw@sisk.pl> Cc: Andreas Herrmann <andreas.herrmann3@amd.com> Cc: stable@vger.kernel.org Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=47301
Diffstat (limited to 'drivers/cpufreq/powernow-k8.c')
1 files changed, 34 insertions, 29 deletions
diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
index c0e816468e30..1a40935c85fd 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;
@@ -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);
- 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 */