| Date | Sun, 14 Oct 2012 15:36:05 +0100 | From | Ben Hutchings <> | Subject | [ 032/147] workqueue: fix possible stall on try_to_grab_pending() of a delayed work item |
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3.2-stable review patch. If anyone has any objections, please let me know.
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From: Lai Jiangshan <laijs@cn.fujitsu.com>
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> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- kernel/workqueue.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-)
--- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1726,10 +1726,9 @@ static void move_linked_works(struct wor *nextp = n; } -static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq) +static void cwq_activate_delayed_work(struct work_struct *work) { - struct work_struct *work = list_first_entry(&cwq->delayed_works, - struct work_struct, entry); + struct cpu_workqueue_struct *cwq = get_work_cwq(work); struct list_head *pos = gcwq_determine_ins_pos(cwq->gcwq, cwq); trace_workqueue_activate_work(work); @@ -1738,6 +1737,14 @@ static void cwq_activate_first_delayed(s cwq->nr_active++; } +static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq) +{ + struct work_struct *work = list_first_entry(&cwq->delayed_works, + struct work_struct, entry); + + cwq_activate_delayed_work(work); +} + /** * cwq_dec_nr_in_flight - decrement cwq's nr_in_flight * @cwq: cwq of interest @@ -2628,6 +2635,18 @@ static int try_to_grab_pending(struct wo smp_rmb(); if (gcwq == get_work_gcwq(work)) { debug_work_deactivate(work); + + /* + * A delayed work item cannot be grabbed directly + * because it might have linked NO_COLOR work items + * which, if left on the delayed_list, will confuse + * cwq->nr_active management later on and cause + * stall. Make sure the work item is activated + * before grabbing. + */ + if (*work_data_bits(work) & WORK_STRUCT_DELAYED) + cwq_activate_delayed_work(work); + list_del_init(&work->entry); cwq_dec_nr_in_flight(get_work_cwq(work), get_work_color(work),
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