On Fri, 20 Apr 2012, Suresh Siddha wrote: > On Fri, 2012-04-20 at 15:47 +0200, Thomas Gleixner wrote: > > On Fri, 20 Apr 2012, Peter Zijlstra wrote: > > > > > On Fri, 2012-04-20 at 13:05 +0000, Thomas Gleixner wrote: > > > > This first part moves the idle thread management for non-boot cpus > > > > into the core. fork_idle() is called in a workqueue as it is > > > > implemented in a few architectures already. This is necessary when not > > > > all cpus are brought up by the early boot code as otherwise we would > > > > take a ref on the user task VM of the thread which brings the cpu up > > > > via the sysfs interface. > > > > > > So I was thinking about this and I think we should make that kthreadd > > > instead of a random workqueue thread due to all that cgroup crap. People > > > are wanting to place all sorts of kernel threads in cgroups and I'm > > > still arguing that kthreadd should not be allowed in cgroups. > > > > So your fear is that the idle_thread will end up in some random cgroup > > because some illdesigned user space code decided to stick kernel > > threads into cgroups. > > > > Can we please have some sanity restrictions on this cgroup muck? I > > don't care when user space creates cgroups in circles, but holding the > > whole kernel hostage of this madness is going too far. > > > > Also, do we really need the workqueue/kthreadd based allocation? Just > like the percpu areas getting allocated for each possible cpu during > boot, shouldn't we extend this to the per-cpu idle threads too? So > something like the appended should be ok to? The idea is correct, there are just a few problems :) > Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx> > --- > diff --git a/kernel/cpu.c b/kernel/cpu.c > index 05c46ba..a5144ab 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -303,10 +303,6 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen) > > cpu_hotplug_begin(); > > - ret = smpboot_prepare(cpu); > - if (ret) > - goto out; > - If we failed to allocate an idle_thread for this cpu in smp_init() then we unconditionally call __cpu_up() with a NULL pointer. That might surprise the arch code :) Aside of that, we now miss to reinitialize the idle thread. We call init_idle() once when we allocate the thread, but not after a cpu offline operation. That might leave stuff in weird state. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
