• Tejun Heo's avatar
    workqueue: restore WQ_UNBOUND/max_active==1 to be ordered · 5c0338c6
    Tejun Heo authored
    The combination of WQ_UNBOUND and max_active == 1 used to imply
    ordered execution.  After NUMA affinity 4c16bd32
    
     ("workqueue:
    implement NUMA affinity for unbound workqueues"), this is no longer
    true due to per-node worker pools.
    
    While the right way to create an ordered workqueue is
    alloc_ordered_workqueue(), the documentation has been misleading for a
    long time and people do use WQ_UNBOUND and max_active == 1 for ordered
    workqueues which can lead to subtle bugs which are very difficult to
    trigger.
    
    It's unlikely that we'd see noticeable performance impact by enforcing
    ordering on WQ_UNBOUND / max_active == 1 workqueues.  Let's
    automatically set __WQ_ORDERED for those workqueues.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Reported-by: default avatarChristoph Hellwig <hch@infradead.org>
    Reported-by: default avatarAlexei Potashnik <alexei@purestorage.com>
    Fixes: 4c16bd32 ("workqueue: implement NUMA affinity for unbound workqueues")
    Cc: stable@vger.kernel.org # v3.10+
    5c0338c6
workqueue.c 155 KB