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>> + int ret; >> + >> + /* Valid input requires a trailing newline */ >> + if (nbytes == 0 || buf[nbytes - 1] != '\n') >> + return -EINVAL; >> + >> + cpus_read_lock(); > Could you please elaborate why this lock is needed here as > well as in the following patch? Holding the cpus_read_lock() make sure that this cpu is online while doing this operation. This code eventually sends an IPI to write the MSR on one of the CPUs using the cpumasks. My understanding is to make sure cpumask is stable while handling this write.  Same thing is done in rdtgroup_schemata_write. Thanks Babu > > Reinette > -- Thanks Babu Moger