diff options
author | Tejun Heo <tj@kernel.org> | 2012-09-18 21:24:59 (GMT) |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2012-09-19 17:15:01 (GMT) |
commit | 6889125b8b4e09c5e53e6ecab3433bed1ce198c9 (patch) | |
tree | f7408140458c2d287014fb66d2b474af01ae9658 | |
parent | ed48ece27cd3d5ee0354c32bbaec0f3e1d4715c3 (diff) | |
download | linux-fsl-qoriq-6889125b8b4e09c5e53e6ecab3433bed1ce198c9.tar.xz |
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
-rw-r--r-- | drivers/cpufreq/powernow-k8.c | 63 |
1 files 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 */ |