pj wrote:
> Could you explain why this is -- what is the deadlock?
On further reading, I see it. You're right.
Deep in the bowels of the hotplug code, when removing a dead cpu, while
holding the runqueue lock (task_rq_lock), the hotplug code might need to
walk up the cpuset hierarchy, to find the nearest enclosing cpuset that
still has online cpus, as part of figuring where to run a task that is
being kicked off the dead cpu. The runqueue lock is atomic, but getting
the cpuset_sem (needed to walk up the cpuset hierarchy) can sleep. So
you need to get the cpuset_sem before calling task_rq_lock, so as to
avoid the "scheduling while atomic" oops that you reported. Therefore
the hotplug code, and anyone else calling cpuset_cpus_allowed(), which
means sched_setaffinity(), needs to first grab cpuset_sem, so that they
can grab any atomic locks needed, after getting cpuset_sem, not before.
Acked-by: Paul Jackson <[email protected]>
--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <[email protected]> 1.650.933.1373, 1.925.600.0401
-
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]