On Thu, 2009-06-25 at 12:46 -0700, Mathieu Desnoyers wrote: > * venkatesh.pallipadi@xxxxxxxxx (venkatesh.pallipadi@xxxxxxxxx) wrote: > > Commit b14893a62c73af0eca414cfed505b8c09efc613c although it was very > > much needed to cleanup ondemand timer cleanly, openup a can of worms > > related to locking dependencies in cpufreq. > > > > Patch here defines the need for dbs_mutex and cleans up its usage in > > ondemand governor. This also resolves the lockdep warnings reported here > > > > http://lkml.indiana.edu/hypermail/linux/kernel/0906.1/01925.html > > > > @@ -598,14 +593,16 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy, > > max(min_sampling_rate, > > latency * LATENCY_MULTIPLIER); > > } > > + mutex_unlock(&dbs_mutex); > > + > > dbs_timer_init(this_dbs_info); > > > > - mutex_unlock(&dbs_mutex); > > break; > > > > case CPUFREQ_GOV_STOP: > > - mutex_lock(&dbs_mutex); > > dbs_timer_exit(this_dbs_info); > > Hrm, so.. how do we protect against concurrent : > > CPUFREQ_GOV_START/CPUFREQ_GOV_STOP now ? concurrent _START _STOP across CPUs does not matter for timer_init and timer_exit. On same CPU, there cannot be two concurrent _START as upper level cpufreq will have policy_rwsem in write mode. I cannot think of a flow where _START and _STOP on same CPU is possible. However two concurrent _STOP for same CPU is still possible, as we are releasing the rwsem lock before STOP callback. "Back to drawing board" time to figure this all out.. Thanks, Venki -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
