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Subject[PATCH 28/31] workqueue: reject increasing max_active for ordered workqueues
Date
Workqueue will soon allow exposing control knobs to userland via
sysfs. Increasing max_active for an ordered workqueue breaks
correctness. Tag ordered workqueues with __WQ_ORDERED and always
limit max_active at 1.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/workqueue.h | 3 ++-
kernel/workqueue.c | 11 ++++++++++-
2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index fc7f882..e1e5748 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -294,6 +294,7 @@ enum {
WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */

__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
+ __WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */

WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
@@ -396,7 +397,7 @@ __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,
* Pointer to the allocated workqueue on success, %NULL on failure.
*/
#define alloc_ordered_workqueue(fmt, flags, args...) \
- alloc_workqueue(fmt, WQ_UNBOUND | (flags), 1, ##args)
+ alloc_workqueue(fmt, WQ_UNBOUND | __WQ_ORDERED | (flags), 1, ##args)

#define create_workqueue(name) \
alloc_workqueue((name), WQ_MEM_RECLAIM, 1)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 2016c9e..8d487f6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3537,7 +3537,16 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
static int wq_clamp_max_active(int max_active, unsigned int flags,
const char *name)
{
- int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
+ int lim;
+
+ if (flags & WQ_UNBOUND) {
+ if (flags & __WQ_ORDERED)
+ lim = 1;
+ else
+ lim = WQ_UNBOUND_MAX_ACTIVE;
+ } else {
+ lim = WQ_MAX_ACTIVE;
+ }

if (max_active < 1 || max_active > lim)
pr_warn("workqueue: max_active %d requested for %s is out of range, clamping between %d and %d\n",
--
1.8.1.2


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