On 01/09, Srivatsa Vaddagiri wrote:
>
> On Tue, Jan 09, 2007 at 06:07:55PM +0300, Oleg Nesterov wrote:
> > but at some point we should thaw processes, including cwq->thread which
> > should die.
>
> I am presuming we will thaw processes after all CPU_DEAD handlers have
> run.
>
> > So we are doing things like take_over_work() and this is the
> > source of races, because the dead CPU is not on cpu_online_map.
> >
> > flush_workqueue() doesn't use any locks now. If we use freezer to implement
> > cpu-hotplug nothing will change, we still have races.
>
> We have races -if- CPU_DEAD handling can run concurrently with a ongoing
> flush_workqueue. From my recent understanding of process freezer, this
> is not possible. In other words, flush_workqueue() can be its old
> implementation as below w/o any races:
>
> some_thread:
>
> for_each_online_cpu(i)
> flush_cpu_workqueue(i);
>
> As long as this loop is running, cpu_down/up will not proceed. This means,
> cpu_online_map is stable even if flush_cpu_workqueue blocks ..
>
> Once this loop is complete and all threads have called try_to_freeze,
> cpu_down will proceed to change the bit map and run CPU_DEAD handlers
> of everyone. I am presuimg we will thaw processes only after all
> CPU_DEAD/ONLINE handlers have run.
We can't do this. We should thaw cwq->thread (which was bound to the
dead CPU) to complete CPU_DEAD event. So we still need some changes.
Oleg.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
