workqueue: fix possible stall on try_to_grab_pending() of a delayed work item
commit 3aa62497594430ea522050b75c033f71f2c60ee6 upstream.
Currently, when try_to_grab_pending() grabs a delayed work item, it
leaves its linked work items alone on the delayed_works. The linked
work items are always NO_COLOR and will cause future
cwq_activate_first_delayed() increase cwq->nr_active incorrectly, and
may cause the whole cwq to stall. For example,
state: cwq->max_active = 1, cwq->nr_active = 1
one work in cwq->pool, many in cwq->delayed_works.
step1: try_to_grab_pending() removes a work item from delayed_works
but leaves its NO_COLOR linked work items on it.
step2: Later on, cwq_activate_first_delayed() activates the linked
work item increasing ->nr_active.
step3: cwq->nr_active = 1, but all activated work items of the cwq are
NO_COLOR. When they finish, cwq->nr_active will not be
decreased due to NO_COLOR, and no further work items will be
activated from cwq->delayed_works. the cwq stalls.
Fix it by ensuring the target work item is activated before stealing
PENDING in try_to_grab_pending(). This ensures that all the linked
work items are activated without incorrectly bumping cwq->nr_active.
tj: Updated comment and description.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
[lizf: backported to 3.4: adjust context]
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed