diff options
| author | Boqun Feng <boqun.feng@gmail.com> | 2021-10-22 08:42:08 +0800 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2021-10-25 07:18:40 -1000 |
| commit | f9eaaa82b474350aa8436d15a7ae150a3c8b9d5c (patch) | |
| tree | 41c1f24760c9aeb8a155dae35ed0b6917158de8c | |
| parent | 55df0933be74bd2e52aba0b67eb743ae0feabe7e (diff) | |
workqueue: doc: Call out the non-reentrance conditions
The current doc of workqueue API suggests that work items are
non-reentrant: any work item is guaranteed to be executed by at most one
worker system-wide at any given time. However this is not true, the
following case can cause a work item W executed by two workers at
the same time:
queue_work_on(0, WQ1, W);
// after a worker picks up W and clear the pending bit
queue_work_on(1, WQ2, W);
// workers on CPU0 and CPU1 will execute W in the same time.
, which means the non-reentrance of a work item is conditional, and
Lai Jiangshan provided a nice summary[1] of the conditions, therefore
use it to describe a work item instance and improve the doc.
[1]: https://lore.kernel.org/lkml/CAJhGHyDudet_xyNk=8xnuO2==o-u06s0E0GZVP4Q67nmQ84Ceg@mail.gmail.com/
Suggested-by: Matthew Wilcox <willy@infradead.org>
Suggested-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
| -rw-r--r-- | Documentation/core-api/workqueue.rst | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/Documentation/core-api/workqueue.rst b/Documentation/core-api/workqueue.rst index 541d31de8926..3b22ed137662 100644 --- a/Documentation/core-api/workqueue.rst +++ b/Documentation/core-api/workqueue.rst @@ -216,10 +216,6 @@ resources, scheduled and executed. This flag is meaningless for unbound wq. -Note that the flag ``WQ_NON_REENTRANT`` no longer exists as all -workqueues are now non-reentrant - any work item is guaranteed to be -executed by at most one worker system-wide at any given time. - ``max_active`` -------------- @@ -391,6 +387,23 @@ the stack trace of the offending worker thread. :: The work item's function should be trivially visible in the stack trace. +Non-reentrance Conditions +========================= + +Workqueue guarantees that a work item cannot be re-entrant if the following +conditions hold after a work item gets queued: + + 1. The work function hasn't been changed. + 2. No one queues the work item to another workqueue. + 3. The work item hasn't been reinitiated. + +In other words, if the above conditions hold, the work item is guaranteed to be +executed by at most one worker system-wide at any given time. + +Note that requeuing the work item (to the same queue) in the self function +doesn't break these conditions, so it's safe to do. Otherwise, caution is +required when breaking the conditions inside a work function. + Kernel Inline Documentations Reference ====================================== |