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https://issues.apache.org/jira/browse/TS-947?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alan M. Carroll reassigned TS-947:
----------------------------------
Assignee: Alan M. Carroll
> AIO Race condition on non NT systems
> ------------------------------------
>
> Key: TS-947
> URL: https://issues.apache.org/jira/browse/TS-947
> Project: Traffic Server
> Issue Type: Bug
> Components: Core
> Environment: stock build with static libts, running on a 4 core server
> Reporter: B Wyatt
> Assignee: Alan M. Carroll
> Fix For: 3.1.2
>
> Attachments: lock-safe-AIO.patch
>
>
> Refer to code below. The timeslice starting when a consumer thread
> determines that the temp_list is empty (A) and ending when it releases the
> aio_mutex(C) is unsafe if the work queues are empty and it breaks loop
> execution at B. During this timeslice (A-C) the consumer holds the aio_mutex
> and as a result request producers enqueue items on the temporary atomic list
> (D). As a consumer in this state will wait for a signal on aio_cond to
> proceed before processing the temp_list again, any requests on the temp_list
> are effectively stalled until a future request produces this signal or
> manually processes the temp_list.
> In the case of cache volume initialization, there is no "future request" and
> the initialization sequence soft locks.
> {code:title=iocore/aio/AIO.cc(annotated)}
> void *
> aio_thread_main(void *arg)
> {
> ...
> ink_mutex_acquire(&my_aio_req->aio_mutex);
> for (;;) {
> do {
> current_req = my_aio_req;
> /* check if any pending requests on the atomic list */
> A>>> if (!INK_ATOMICLIST_EMPTY(my_aio_req->aio_temp_list))
> aio_move(my_aio_req);
> if (!(op = my_aio_req->aio_todo.pop()) && !(op =
> my_aio_req->http_aio_todo.pop()))
> B>>> break;
> ...
> <<service request>>
> ...
> } while (1);
> C>>>ink_cond_wait(&my_aio_req->aio_cond, &my_aio_req->aio_mutex);
> }
> ...
> }
> static void
> aio_queue_req(AIOCallbackInternal *op, int fromAPI = 0)
> {
> ...
> if (!ink_mutex_try_acquire(&req->aio_mutex)) {
> D>>>ink_atomiclist_push(&req->aio_temp_list, op);
> } else {
> /* check if any pending requests on the atomic list */
> if (!INK_ATOMICLIST_EMPTY(req->aio_temp_list))
> aio_move(req);
> /* now put the new request */
> aio_insert(op, req);
> ink_cond_signal(&req->aio_cond);
> ink_mutex_release(&req->aio_mutex);
> }
> ...
> }
> {code}
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