From: Prakash Surya Date: Fri, 16 Dec 2011 17:44:31 +0000 (-0800) Subject: Swap taskq_ent_t with taskqid_t in taskq_thread_t X-Git-Tag: zfs-0.8.0-rc1~152^2~418 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=e7e5f78e7bf6dc86337483f4d9f01becc017d185;p=zfs Swap taskq_ent_t with taskqid_t in taskq_thread_t The taskq_t's active thread list is sorted based on its tqt_ent->tqent_id field. The list is kept sorted solely by inserting new taskq_thread_t's in their correct sorted location; no other means is used. This means that once inserted, if a taskq_thread_t's tqt_ent->tqent_id field changes, the list runs the risk of no longer being sorted. Prior to the introduction of the taskq_dispatch_prealloc() interface, this was not a problem as a taskq_ent_t actively being serviced under the old interface should always have a static tqent_id field. Thus, once the taskq_thread_t is added to the taskq_t's active thread list, the taskq_thread_t's tqt_ent->tqent_id field would remain constant. Now, this is no longer the case. Currently, if using the taskq_dispatch_prealloc() interface, any given taskq_ent_t actively being serviced _may_ have its tqent_id value incremented. This happens when the preallocated taskq_ent_t structure is recursively dispatched. Thus, a taskq_thread_t could potentially have its tqt_ent->tqent_id field silently modified from under its feet. If this were to happen to a taskq_thread_t on a taskq_t's active thread list, this would compromise the integrity of the order of the list (as the list _may_ no longer be sorted). To get around this, the taskq_thread_t's taskq_ent_t pointer was replaced with its own static copy of the tqent_id. So, as a taskq_ent_t is pulled off of the taskq_t's pending list, a static copy of its tqent_id is made and this copy is used to sort the active thread list. Using a static copy is key in ensuring the integrity of the order of the active thread list. Even if the underlying taskq_ent_t is recursively dispatched (as has its tqent_id modified), this static copy stored inside the taskq_thread_t will remain constant. Signed-off-by: Prakash Surya Signed-off-by: Brian Behlendorf Issue #71 --- diff --git a/include/sys/taskq.h b/include/sys/taskq.h index 54d869afe..0a7143375 100644 --- a/include/sys/taskq.h +++ b/include/sys/taskq.h @@ -96,7 +96,7 @@ typedef struct taskq_thread { struct list_head tqt_active_list; struct task_struct *tqt_thread; taskq_t *tqt_tq; - taskq_ent_t *tqt_ent; + taskqid_t tqt_id; } taskq_thread_t; /* Global system-wide dynamic task queue available for all consumers */ diff --git a/module/spl/spl-taskq.c b/module/spl/spl-taskq.c index b2b0e6ca8..ccb713c20 100644 --- a/module/spl/spl-taskq.c +++ b/module/spl/spl-taskq.c @@ -393,8 +393,8 @@ taskq_lowest_id(taskq_t *tq) if (!list_empty(&tq->tq_active_list)) { tqt = list_entry(tq->tq_active_list.next, taskq_thread_t, tqt_active_list); - ASSERT(tqt->tqt_ent != NULL); - lowest_id = MIN(lowest_id, tqt->tqt_ent->tqent_id); + ASSERT(tqt->tqt_id != 0); + lowest_id = MIN(lowest_id, tqt->tqt_id); } SRETURN(lowest_id); @@ -417,7 +417,7 @@ taskq_insert_in_order(taskq_t *tq, taskq_thread_t *tqt) list_for_each_prev(l, &tq->tq_active_list) { w = list_entry(l, taskq_thread_t, tqt_active_list); - if (w->tqt_ent->tqent_id < tqt->tqt_ent->tqent_id) { + if (w->tqt_id < tqt->tqt_id) { list_add(&tqt->tqt_active_list, l); break; } @@ -433,7 +433,6 @@ taskq_thread(void *args) { DECLARE_WAITQUEUE(wait, current); sigset_t blocked; - taskqid_t id; taskq_thread_t *tqt = args; taskq_t *tq; taskq_ent_t *t; @@ -484,8 +483,7 @@ taskq_thread(void *args) /* In order to support recursively dispatching a * preallocated taskq_ent_t, tqent_id must be * stored prior to executing tqent_func. */ - id = t->tqent_id; - tqt->tqt_ent = t; + tqt->tqt_id = t->tqent_id; taskq_insert_in_order(tq, tqt); tq->tq_nactive++; spin_unlock_irqrestore(&tq->tq_lock, tq->tq_lock_flags); @@ -496,16 +494,16 @@ taskq_thread(void *args) spin_lock_irqsave(&tq->tq_lock, tq->tq_lock_flags); tq->tq_nactive--; list_del_init(&tqt->tqt_active_list); - tqt->tqt_ent = NULL; task_done(tq, t); /* When the current lowest outstanding taskqid is * done calculate the new lowest outstanding id */ - if (tq->tq_lowest_id == id) { + if (tq->tq_lowest_id == tqt->tqt_id) { tq->tq_lowest_id = taskq_lowest_id(tq); - ASSERT(tq->tq_lowest_id > id); + ASSERT3S(tq->tq_lowest_id, >, tqt->tqt_id); } + tqt->tqt_id = 0; wake_up_all(&tq->tq_wait_waitq); } @@ -582,7 +580,7 @@ __taskq_create(const char *name, int nthreads, pri_t pri, INIT_LIST_HEAD(&tqt->tqt_thread_list); INIT_LIST_HEAD(&tqt->tqt_active_list); tqt->tqt_tq = tq; - tqt->tqt_ent = NULL; + tqt->tqt_id = 0; tqt->tqt_thread = kthread_create(taskq_thread, tqt, "%s/%d", name, i);