Hello, Johannes.
On Fri, May 05, 2023 at 11:05:45PM +0200, Johannes Berg wrote:
...
> The implementation of (2) is a bit ... awkward, @Tejun, @Lai, there's no
> way to "pause" an ordered workqueue, is there? I came up with the below
> patch, but it's a bit ugly and requires a lot of context switches. Just
> flushing isn't enough since then some work might start and hang on
> acquiring the lock.
There isn't currently but workqueue already does something similar for
freezing by temporarily setting max_active to zero, so if you apply a patch
like the following
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b8b541caed48..6daf9ee7450d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4360,11 +4360,11 @@ static int wq_clamp_max_active(int max_active, unsigned int flags,
{
int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
- if (max_active < 1 || max_active > lim)
+ if (max_active < 0 || max_active > lim)
pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
max_active, name, 1, lim);
- return clamp_val(max_active, 1, lim);
+ return clamp_val(max_active, 0, lim);
}
/*
@@ -4625,7 +4625,8 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
struct pool_workqueue *pwq;
/* disallow meddling with max_active for ordered workqueues */
- if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
+ if (WARN_ON((wq->flags & __WQ_ORDERED_EXPLICIT) &&
+ max_active != 0 && max_active != 1))
return;
max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
and then do set_max_active(wq, 0) followed by flush_workqueue(), it should
be paused until max_active is restored to 1. It probably would be better to
add a separate pause / resume interface which sets a per-wq flag which is
read by pwq_adjust_max_active() tho. Anyways, it's not difficult to
implement at all.
Thanks.
--
tejun
