From: Lai Jiangshan laijs@linux.alibaba.com
mainline inclusion from mainline-v5.15-rc1 commit 018f3a13dd6300701103f268b6bfec0a56beea57 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I7LRJF
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Currently, WORK_NO_COLOR has two meanings: Not participate in flushing Not participate in nr_active
And only non-barrier work items are marked with WORK_STRUCT_INACTIVE when they are in inactive_works list. The barrier work items are not marked INACTIVE even linked in inactive_works list since these tail items are always moved together with the head work item.
These definitions are simple, clean and practical. (Except a small blemish that only the first meaning of WORK_NO_COLOR is documented in include/linux/workqueue.h while both meanings are in workqueue.c)
But dual-purpose WORK_NO_COLOR used for barrier work items has proven to be problematical[1]. Only the second purpose is obligatory. So we plan to make barrier work items participate in flushing but keep them still not participating in nr_active.
So the plan is to mark barrier work items inactive without using WORK_NO_COLOR in this patch so that we can assign a flushing color to them in next patch.
The reasonable way is to add or reuse a bit in work data of the work item. But adding a bit will double the size of pool_workqueue.
Currently, WORK_STRUCT_INACTIVE is only used in try_to_grab_pending() for user-queued work items and try_to_grab_pending() can't work for barrier work items. So we extend WORK_STRUCT_INACTIVE to also mark barrier work items no matter which list they are in because we don't need to determind which list a barrier work item is in.
So the meaning of WORK_STRUCT_INACTIVE becomes just "the work items don't participate in nr_active" (no matter whether it is a barrier work item or a user-queued work item). And WORK_STRUCT_INACTIVE for user-queued work items means they are in inactive_works list.
This patch does it by setting WORK_STRUCT_INACTIVE for barrier work items in insert_wq_barrier() and checking WORK_STRUCT_INACTIVE first in pwq_dec_nr_in_flight(). And the meaning of WORK_NO_COLOR is reduced to only "not participating in flushing".
There is no functionality change intended in this patch. Because WORK_NO_COLOR+WORK_STRUCT_INACTIVE represents the previous WORK_NO_COLOR in meaning and try_to_grab_pending() doesn't use for barrier work items and avoids being confused by this extended WORK_STRUCT_INACTIVE.
A bunch of comment for nr_active & WORK_STRUCT_INACTIVE is also added for documenting how WORK_STRUCT_INACTIVE works in nr_active management.
[1]: https://lore.kernel.org/lkml/20210812083814.32453-1-lizhe.67@bytedance.com/ Signed-off-by: Lai Jiangshan laijs@linux.alibaba.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Zeng Heng zengheng4@huawei.com --- kernel/workqueue.c | 42 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 34 insertions(+), 8 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 9acd0941401a..ef049b6a26a4 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -205,6 +205,23 @@ struct pool_workqueue { int refcnt; /* L: reference count */ int nr_in_flight[WORK_NR_COLORS]; /* L: nr of in_flight works */ + + /* + * nr_active management and WORK_STRUCT_INACTIVE: + * + * When pwq->nr_active >= max_active, new work item is queued to + * pwq->inactive_works instead of pool->worklist and marked with + * WORK_STRUCT_INACTIVE. + * + * All work items marked with WORK_STRUCT_INACTIVE do not participate + * in pwq->nr_active and all work items in pwq->inactive_works are + * marked with WORK_STRUCT_INACTIVE. But not all WORK_STRUCT_INACTIVE + * work items are in pwq->inactive_works. Some of them are ready to + * run in pool->worklist or worker->scheduled. Those work itmes are + * only struct wq_barrier which is used for flush_work() and should + * not participate in pwq->nr_active. For non-barrier work item, it + * is marked with WORK_STRUCT_INACTIVE iff it is in pwq->inactive_works. + */ int nr_active; /* L: nr of active works */ int max_active; /* L: max active works */ struct list_head inactive_works; /* L: inactive works */ @@ -1140,19 +1157,21 @@ static void pwq_dec_nr_in_flight(struct pool_workqueue *pwq, unsigned long work_ { int color = get_work_color(work_data);
- /* uncolored work items don't participate in flushing or nr_active */ + if (!(work_data & WORK_STRUCT_INACTIVE)) { + pwq->nr_active--; + if (!list_empty(&pwq->inactive_works)) { + /* one down, submit an inactive one */ + if (pwq->nr_active < pwq->max_active) + pwq_activate_first_inactive(pwq); + } + } + + /* uncolored work items don't participate in flushing */ if (color == WORK_NO_COLOR) goto out_put;
pwq->nr_in_flight[color]--;
- pwq->nr_active--; - if (!list_empty(&pwq->inactive_works)) { - /* one down, submit an inactive one */ - if (pwq->nr_active < pwq->max_active) - pwq_activate_first_inactive(pwq); - } - /* is flush in progress and are we at the flushing tip? */ if (likely(pwq->flush_color != color)) goto out_put; @@ -1248,6 +1267,10 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork, debug_work_deactivate(work);
/* + * A cancelable inactive work item must be in the + * pwq->inactive_works since a queued barrier can't be + * canceled (see the comments in insert_wq_barrier()). + * * An inactive work item cannot be grabbed directly because * it might have linked NO_COLOR work items which, if left * on the inactive_works list, will confuse pwq->nr_active @@ -2641,6 +2664,9 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
barr->task = current;
+ /* The barrier work item does not participate in pwq->nr_active. */ + work_flags |= WORK_STRUCT_INACTIVE; + /* * If @target is currently being executed, schedule the * barrier to the worker; otherwise, put it after @target.