2019-07-25 21:26:12

by Daniel Jordan

Subject: [RFC 3/9] workqueue: require CPU hotplug read exclusion for apply_workqueue_attrs

Change the calling convention for apply_workqueue_attrs to require CPU
hotplug read exclusion.

Avoids lockdep complaints about nested calls to get_online_cpus in a
future patch where padata calls apply_workqueue_attrs when changing
other CPU-hotplug-sensitive data structures with the CPU read lock
already held.

Signed-off-by: Daniel Jordan <[email protected]>
---
kernel/workqueue.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f53705ff3ff1..bc2e09a8ea61 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4030,6 +4030,8 @@ static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
*
* Performs GFP_KERNEL allocations.
*
+ * Assumes caller has CPU hotplug read exclusion, i.e. get_online_cpus().
+ *
* Return: 0 on success and -errno on failure.
*/
int apply_workqueue_attrs(struct workqueue_struct *wq,
@@ -4037,9 +4039,11 @@ int apply_workqueue_attrs(struct workqueue_struct *wq,
{
int ret;

- apply_wqattrs_lock();
+ lockdep_assert_cpus_held();
+
+ mutex_lock(&wq_pool_mutex);
ret = apply_workqueue_attrs_locked(wq, attrs);
- apply_wqattrs_unlock();
+ mutex_unlock(&wq_pool_mutex);

return ret;
}
@@ -4152,16 +4156,21 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
mutex_unlock(&wq->mutex);
}
return 0;
- } else if (wq->flags & __WQ_ORDERED) {
+ }
+
+ get_online_cpus();
+ if (wq->flags & __WQ_ORDERED) {
ret = apply_workqueue_attrs(wq, ordered_wq_attrs[highpri]);
/* there should only be single pwq for ordering guarantee */
WARN(!ret && (wq->pwqs.next != &wq->dfl_pwq->pwqs_node ||
wq->pwqs.prev != &wq->dfl_pwq->pwqs_node),
"ordering guarantee broken for workqueue %s\n", wq->name);
- return ret;
} else {
- return apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
+ ret = apply_workqueue_attrs(wq, unbound_std_wq_attrs[highpri]);
}
+ put_online_cpus();
+
+ return ret;
}

static int wq_clamp_max_active(int max_active, unsigned int flags,
--
2.22.0

2019-07-29 20:05:23

by Tejun Heo

Subject: Re: [RFC 3/9] workqueue: require CPU hotplug read exclusion for apply_workqueue_attrs

On Thu, Jul 25, 2019 at 05:24:59PM -0400, Daniel Jordan wrote:
> Change the calling convention for apply_workqueue_attrs to require CPU
> hotplug read exclusion.
>
> Avoids lockdep complaints about nested calls to get_online_cpus in a
> future patch where padata calls apply_workqueue_attrs when changing
> other CPU-hotplug-sensitive data structures with the CPU read lock
> already held.
>
> Signed-off-by: Daniel Jordan <[email protected]>

Acked-by: Tejun Heo <[email protected]>

Please feel free to route with the rest of the patchset.

Thanks.

--
tejun

2019-07-30 04:37:59

by Daniel Jordan

Subject: Re: [RFC 3/9] workqueue: require CPU hotplug read exclusion for apply_workqueue_attrs

On Mon, Jul 29, 2019 at 12:47:21PM -0700, Tejun Heo wrote:
> On Thu, Jul 25, 2019 at 05:24:59PM -0400, Daniel Jordan wrote:
> > Change the calling convention for apply_workqueue_attrs to require CPU
> > hotplug read exclusion.
> >
> > Avoids lockdep complaints about nested calls to get_online_cpus in a
> > future patch where padata calls apply_workqueue_attrs when changing
> > other CPU-hotplug-sensitive data structures with the CPU read lock
> > already held.
> >
> > Signed-off-by: Daniel Jordan <[email protected]>
>
> Acked-by: Tejun Heo <[email protected]>

Thanks, Tejun!