Hi Steve, On Wed, Dec 9, 2015 at 2:19 PM, Steve Muckle <steve.muc...@linaro.org> wrote:
[...] > +/* > + * we pass in struct cpufreq_policy. This is safe because changing out the > + * policy requires a call to __cpufreq_governor(policy, CPUFREQ_GOV_STOP), > + * which tears down all of the data structures and __cpufreq_governor(policy, > + * CPUFREQ_GOV_START) will do a full rebuild, including this kthread with the > + * new policy pointer > + */ > +static int cpufreq_sched_thread(void *data) > +{ > + struct sched_param param; > + struct cpufreq_policy *policy; > + struct gov_data *gd; > + unsigned int new_request = 0; > + unsigned int last_request = 0; > + int ret; > + > + policy = (struct cpufreq_policy *) data; > + gd = policy->governor_data; > + > + param.sched_priority = 50; > + ret = sched_setscheduler_nocheck(gd->task, SCHED_FIFO, ¶m); > + if (ret) { > + pr_warn("%s: failed to set SCHED_FIFO\n", __func__); > + do_exit(-EINVAL); > + } else { > + pr_debug("%s: kthread (%d) set to SCHED_FIFO\n", > + __func__, gd->task->pid); > + } > + > + do { > + set_current_state(TASK_INTERRUPTIBLE); > + new_request = gd->requested_freq; > + if (new_request == last_request) { > + schedule(); Should we check kthread_should_stop() after set_current_state(TASK_INTERRUPTIBLE), probably right before schedule()? Something like: set_current_state(TASK_INTERRUPTIBLE); new_request = gd->requested_freq; if (new_request == last_request) { if (kthread_should_stop()) break; schedule(); } else { ... } On the previous version of the scheduler-driver cpu frequency selection I had the following: <3>[ 1920.233598] INFO: task autotest:32443 blocked for more than 120 seconds. <3>[ 1920.233625] Not tainted 3.18.0-09696-g4312b25 #1 <3>[ 1920.233641] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. <6>[ 1920.233659] autotest D ffffffc0002057a0 0 32443 32403 0x00400000 <0>[ 1920.233693] Call trace: <4>[ 1920.233724] [<ffffffc0002057a0>] __switch_to+0x80/0x8c <4>[ 1920.233748] [<ffffffc000897908>] __schedule+0x550/0x7d8 <4>[ 1920.233769] [<ffffffc000897c08>] schedule+0x78/0x84 <4>[ 1920.233786] [<ffffffc00089bf9c>] schedule_timeout+0x40/0x2ac <4>[ 1920.233804] [<ffffffc000898960>] wait_for_common+0x154/0x18c <4>[ 1920.233820] [<ffffffc0008989bc>] wait_for_completion+0x24/0x34 <4>[ 1920.233840] [<ffffffc000242f84>] kthread_stop+0x130/0x22c <4>[ 1920.233859] [<ffffffc00026ce84>] cpufreq_sched_setup+0x21c/0x308 <4>[ 1920.233881] [<ffffffc0006dcd30>] __cpufreq_governor+0x114/0x1c8 <4>[ 1920.233901] [<ffffffc0006dd168>] cpufreq_set_policy+0x120/0x1b8 <4>[ 1920.233920] [<ffffffc0006ddb64>] store_scaling_governor+0x8c/0xd4 <4>[ 1920.233937] [<ffffffc0006dc494>] store+0x98/0xd0 <4>[ 1920.233958] [<ffffffc0003b4158>] sysfs_kf_write+0x54/0x64 <4>[ 1920.233977] [<ffffffc0003b34d0>] kernfs_fop_write+0x108/0x150 <4>[ 1920.233999] [<ffffffc000344d2c>] vfs_write+0xc4/0x1a0 <4>[ 1920.234018] [<ffffffc000345478>] SyS_write+0x60/0xb4 <4>[ 1920.234031] INFO: lockdep is turned off. <6>[ 1920.234043] task PC stack pid father <6>[ 1920.234161] autotest D ffffffc0002057a0 0 32443 32403 0x00400000 <0>[ 1920.234193] Call trace: <4>[ 1920.234211] [<ffffffc0002057a0>] __switch_to+0x80/0x8c <4>[ 1920.234232] [<ffffffc000897908>] __schedule+0x550/0x7d8 <4>[ 1920.234251] [<ffffffc000897c08>] schedule+0x78/0x84 <4>[ 1920.234268] [<ffffffc00089bf9c>] schedule_timeout+0x40/0x2ac <4>[ 1920.234285] [<ffffffc000898960>] wait_for_common+0x154/0x18c <4>[ 1920.234301] [<ffffffc0008989bc>] wait_for_completion+0x24/0x34 <4>[ 1920.234319] [<ffffffc000242f84>] kthread_stop+0x130/0x22c <4>[ 1920.234335] [<ffffffc00026ce84>] cpufreq_sched_setup+0x21c/0x308 <4>[ 1920.234355] [<ffffffc0006dcd30>] __cpufreq_governor+0x114/0x1c8 <4>[ 1920.234375] [<ffffffc0006dd168>] cpufreq_set_policy+0x120/0x1b8 <4>[ 1920.234395] [<ffffffc0006ddb64>] store_scaling_governor+0x8c/0xd4 <4>[ 1920.234413] [<ffffffc0006dc494>] store+0x98/0xd0 <4>[ 1920.234432] [<ffffffc0003b4158>] sysfs_kf_write+0x54/0x64 <4>[ 1920.234449] [<ffffffc0003b34d0>] kernfs_fop_write+0x108/0x150 <4>[ 1920.234470] [<ffffffc000344d2c>] vfs_write+0xc4/0x1a0 <4>[ 1920.234489] [<ffffffc000345478>] SyS_write+0x60/0xb4 This happened while the kernel is switching from the sched governor to the userspace governor. There's a race between kthread_stop() and cpufreq_sched_thread(). On the previous version I was testing, I can easily reproduce the lockup if I add a msleep(100) right before set_current_state(TASK_INTERRUPTIBLE), and then switching between the two governors through sysfs. > + } else { > + /* > + * if the frequency thread sleeps while waiting to be > + * unthrottled, start over to check for a newer > request > + */ > + if (finish_last_request(gd)) > + continue; > + last_request = new_request; > + cpufreq_sched_try_driver_target(policy, new_request); > + } > + } while (!kthread_should_stop()); > + > + return 0; > +} [...] Best, Ricky