* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > Yet another kernel thread for each CPU. All because of some dung > > > way down in arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.c. > > > > > > Is there no other way? > > > > Perhaps, but this works. Trying to be clever got me into this mess in > > the first place. > > > > We could stop using workqueues and change work_on_cpu to create a > > thread every time, which would give it a new failure mode so I don't > > know that everyone could use it any more. Or we could keep a single > > thread around to do all the cpus, and duplicate much of the workqueue > > code. > > > > None of these options are appealing... > > Can we try harder please? 10 screenfuls of kernel threads in the ps > output is just irritating. > > How about banning the use of work_on_cpu() from schedule_work() handlers > and then fixing that driver somehow? Yes, but that's fundamentally fragile: anyone who happens to stick the wrong thing into keventd (and it's dead easy because schedule_work() is easy to use) will lock up work_on_cpu() users. work_on_cpu() is an important (and lowlevel enough) facility to be isolated from casual interaction like that. > What _is_ the bug anyway? The only description we were given was > > Impact: remove potential clashes with generic kevent workqueue > > Annoyingly, some places we want to use work_on_cpu are already in > workqueues. As per Ingo's suggestion, we create a different > workqueue for work_on_cpu. > > which didn't bother telling anyone squat. > > When was this bug added? Was it added into that driver or was it due to > infrastructural changes? This fixes lockups during bootup caused by the cpumask changes/cleanups which changed set_cpus_allowed()+on-kernel-stack-cpumask_t to work_on_cpu(). Which was fine except it didnt take into account the interaction with the kevents workqueue and the very wide cross section for worklet dependencies that this brings with itself. work_on_cpu() was rarely used before so this didnt show up. Ingo -- 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
