Benjamin Herrenschmidt <b...@kernel.crashing.org> writes: > On Mon, 2018-01-08 at 21:30 -0800, John Sperbeck wrote: >> The pnv_get_proc_freq() function was recently changed to call >> cpufreq_get(), instead of cpufreq_quick_get(), in order to fetch >> a more up-to-date value for the CPU frequency: >> >> cd77b5ce208c153260ed7882d8910f2395bfaabd >> powerpc/powernv/cpufreq: Fix the frequency read by /proc/cpuinfo >> >> Unfortunately, this function is called from show_cpuinfo() in >> arch/powerpc/kernel/setup-common.c with preemption disabled. The >> cpufreq_get() function might do a down_read(), which can sleep. >> >> With CONFIG_DEBUG_KERNEL and CONFIG_DEBUG_ATOMIC_SLEEP set, a warning >> like the following is generated when running 'cat /proc/cpuinfo':
This was reported by Nick back in November just a few days after the patch went in, so it's a little disappointing that it's still broken. > We could just either remove the preempt_disable completely like > x86 and keep it racy, or stick a cpus_read_lock around it. I dont think > we need that preempt_disable, it's definitely overkill. > > Michael, what do you think ? I'm keen on sync'ing with x86 here... Yeah I think we can drop it. The cpufreq seems to have some locking that looks like it'll probably work - famous last words. Who's writing the patch? cheers
