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    Subject[PATCH UPDATED 28/31] workqueue: reject adjusting max_active or applying attrs to ordered workqueues
    Adjusting max_active of or applying new workqueue_attrs to an ordered
    workqueue breaks its ordering guarantee. The former is obvious. The
    latter is because applying attrs creates a new pwq (pool_workqueue)
    and there is no ordering constraint between the old and new pwqs.

    Make apply_workqueue_attrs() and workqueue_set_max_active() trigger
    WARN_ON() if those operations are requested on an ordered workqueue
    and fail / ignore respectively.

    Signed-off-by: Tejun Heo <tj@kernel.org>
    ---
    include/linux/workqueue.h | 3 ++-
    kernel/workqueue.c | 9 +++++++++
    2 files changed, 11 insertions(+), 1 deletion(-)

    --- 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, u
    * 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)
    --- a/kernel/workqueue.c
    +++ b/kernel/workqueue.c
    @@ -3487,9 +3487,14 @@ int apply_workqueue_attrs(struct workque
    struct pool_workqueue *pwq, *last_pwq;
    struct worker_pool *pool;

    + /* only unbound workqueues can change attributes */
    if (WARN_ON(!(wq->flags & WQ_UNBOUND)))
    return -EINVAL;

    + /* creating multiple pwqs breaks ordering guarantee */
    + if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
    + return -EINVAL;
    +
    pwq = kmem_cache_zalloc(pwq_cache, GFP_KERNEL);
    if (!pwq)
    return -ENOMEM;
    @@ -3745,6 +3750,10 @@ void workqueue_set_max_active(struct wor
    {
    struct pool_workqueue *pwq;

    + /* disallow meddling with max_active for ordered workqueues */
    + if (WARN_ON(wq->flags & __WQ_ORDERED))
    + return;
    +
    max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);

    spin_lock_irq(&workqueue_lock);

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      Last update: 2013-03-04 20:02    [W:11.777 / U:0.004 seconds]
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