Messages in this thread | | | Subject | Re: [PATCH] workqueue: Ensure that cpumask set for pools created after boot | From | Michael Bringmann <> | Date | Mon, 15 May 2017 10:48:04 -0500 |
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Hello:
On 05/10/2017 12:33 PM, Tejun Heo wrote: > Hello, > > On Wed, May 10, 2017 at 11:48:17AM -0500, Michael Bringmann wrote: >> >> On NUMA systems with dynamic processors, the content of the cpumask >> may change over time. As new processors are added via DLPAR operations, >> workqueues are created for them. This patch ensures that the pools >> created for new workqueues will be initialized with a cpumask before >> the first worker is created, attached, and woken up. If the mask is >> not set up, then the kernel will crash when 'wakeup_process' is unable >> to find a valid CPU to which to assign the new worker. >> >> Signed-off-by: Michael Bringmann <mwb@linux.vnet.ibm.com> >> --- >> diff --git a/kernel/workqueue.c b/kernel/workqueue.c >> index c74bf39..6091069 100644 >> --- a/kernel/workqueue.c >> +++ b/kernel/workqueue.c >> @@ -3366,6 +3366,8 @@ static struct worker_pool *get_unbound_pool(const struct workqueue_attrs *attrs) >> copy_workqueue_attrs(pool->attrs, attrs); >> pool->node = target_node; >> >> + cpumask_copy(pool->attrs->cpumask, cpumask_of(smp_processor_id())); > > What prevents a cpu getting added right here tho?
PowerPC has only one control path to add/remove CPUs via DLPAR operations. Even so, the underlying code is protected through multiple locks.
> > Maybe the right thing to do is protecting the whole thing with hotplug > readlock?
The operation is already within a hotplug readlock when performing DLPAR add/remove. Adding a CPU to the system, requires it to be brought online. Removing a CPU from the system, requires it to be taken offline. These involve calls to cpu_up / cpu_down, which go through _cpu_up / _cpu_down, which acquire the hotplug locks, among others along the path of execution.
The locks are acquired before getting to the workqueue code, the pool creation/attachment code (which is where the cpu mask needs to be set), or trying to wakeup the initial created task in 'sched.c'.
> > Thanks. >
Regards, Michael
-- Michael W. Bringmann Linux Technology Center IBM Corporation Tie-Line 363-5196 External: (512) 286-5196 Cell: (512) 466-0650 mwb@linux.vnet.ibm.com
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