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authorTejun Heo <tj@kernel.org>2013-01-22 16:15:15 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-01-27 20:49:00 -0800
commit9b19e974ebb8ae156e03a6ad7361b8c7134e68a0 (patch)
tree520db99e911957c18a42b95539928134d127dfdd
parent00112dc1bf0af8f50cd7f7c8008eb4230e8db5d7 (diff)
downloadlwn-9b19e974ebb8ae156e03a6ad7361b8c7134e68a0.tar.gz
lwn-9b19e974ebb8ae156e03a6ad7361b8c7134e68a0.zip
async: fix __lowest_in_progress()
commit f56c3196f251012de9b3ebaff55732a9074fdaae upstream. Commit 083b804c4d3e ("async: use workqueue for worker pool") made it possible that async jobs are moved from pending to running out-of-order. While pending async jobs will be queued and dispatched for execution in the same order, nothing guarantees they'll enter "1) move self to the running queue" of async_run_entry_fn() in the same order. Before the conversion, async implemented its own worker pool. An async worker, upon being woken up, fetches the first item from the pending list, which kept the executing lists sorted. The conversion to workqueue was done by adding work_struct to each async_entry and async just schedules the work item. The queueing and dispatching of such work items are still in order but now each worker thread is associated with a specific async_entry and moves that specific async_entry to the executing list. So, depending on which worker reaches that point earlier, which is non-deterministic, we may end up moving an async_entry with larger cookie before one with smaller one. This broke __lowest_in_progress(). running->domain may not be properly sorted and is not guaranteed to contain lower cookies than pending list when not empty. Fix it by ensuring sort-inserting to the running list and always looking at both pending and running when trying to determine the lowest cookie. Over time, the async synchronization implementation became quite messy. We better restructure it such that each async_entry is linked to two lists - one global and one per domain - and not move it when execution starts. There's no reason to distinguish pending and running. They behave the same for synchronization purposes. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/async.c27
1 files changed, 20 insertions, 7 deletions
diff --git a/kernel/async.c b/kernel/async.c
index 9d3118384858..8f9f5cf001be 100644
--- a/kernel/async.c
+++ b/kernel/async.c
@@ -86,18 +86,27 @@ static atomic_t entry_count;
*/
static async_cookie_t __lowest_in_progress(struct async_domain *running)
{
+ async_cookie_t first_running = next_cookie; /* infinity value */
+ async_cookie_t first_pending = next_cookie; /* ditto */
struct async_entry *entry;
+ /*
+ * Both running and pending lists are sorted but not disjoint.
+ * Take the first cookies from both and return the min.
+ */
if (!list_empty(&running->domain)) {
entry = list_first_entry(&running->domain, typeof(*entry), list);
- return entry->cookie;
+ first_running = entry->cookie;
}
- list_for_each_entry(entry, &async_pending, list)
- if (entry->running == running)
- return entry->cookie;
+ list_for_each_entry(entry, &async_pending, list) {
+ if (entry->running == running) {
+ first_pending = entry->cookie;
+ break;
+ }
+ }
- return next_cookie; /* "infinity" value */
+ return min(first_running, first_pending);
}
static async_cookie_t lowest_in_progress(struct async_domain *running)
@@ -118,13 +127,17 @@ static void async_run_entry_fn(struct work_struct *work)
{
struct async_entry *entry =
container_of(work, struct async_entry, work);
+ struct async_entry *pos;
unsigned long flags;
ktime_t uninitialized_var(calltime), delta, rettime;
struct async_domain *running = entry->running;
- /* 1) move self to the running queue */
+ /* 1) move self to the running queue, make sure it stays sorted */
spin_lock_irqsave(&async_lock, flags);
- list_move_tail(&entry->list, &running->domain);
+ list_for_each_entry_reverse(pos, &running->domain, list)
+ if (entry->cookie < pos->cookie)
+ break;
+ list_move_tail(&entry->list, &pos->list);
spin_unlock_irqrestore(&async_lock, flags);
/* 2) run (and print duration) */