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authorNeilBrown <neilb@suse.de>2011-04-11 14:13:10 +0200
committerJens Axboe <jaxboe@fusionio.com>2011-04-11 14:13:10 +0200
commit109b81296c63228578d4760794d8dd46e02eddfb (patch)
tree2f723e1b69ab08e12528f677f04edbfc7473b7c5
parent4263a2f1dad8c8e7ce2352a0cbc882c2b0c044a9 (diff)
block: splice plug list to local context
If the request_fn ends up blocking, we could be re-entering the plug flush. Since the list is protected by explicitly not allowing schedule events, this isn't a terribly good idea. Additionally, it can cause us to recurse. As request_fn called by __blk_run_queue is allowed to 'schedule()' (after dropping the queue lock of course), it is possible to get a recursive call: schedule -> blk_flush_plug -> __blk_finish_plug -> flush_plug_list -> __blk_run_queue -> request_fn -> schedule We must make sure that the second schedule does not call into blk_flush_plug again. So instead of leaving the list of requests on blk_plug->list, move them to a separate list leaving blk_plug->list empty. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
-rw-r--r--block/blk-core.c14
1 files changed, 9 insertions, 5 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 90f22cc3079..eeaca0998df 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2673,19 +2673,24 @@ static void flush_plug_list(struct blk_plug *plug)
struct request_queue *q;
unsigned long flags;
struct request *rq;
+ LIST_HEAD(list);
BUG_ON(plug->magic != PLUG_MAGIC);
if (list_empty(&plug->list))
return;
- if (plug->should_sort)
- list_sort(NULL, &plug->list, plug_rq_cmp);
+ list_splice_init(&plug->list, &list);
+
+ if (plug->should_sort) {
+ list_sort(NULL, &list, plug_rq_cmp);
+ plug->should_sort = 0;
+ }
q = NULL;
local_irq_save(flags);
- while (!list_empty(&plug->list)) {
- rq = list_entry_rq(plug->list.next);
+ while (!list_empty(&list)) {
+ rq = list_entry_rq(list.next);
list_del_init(&rq->queuelist);
BUG_ON(!(rq->cmd_flags & REQ_ON_PLUG));
BUG_ON(!rq->q);
@@ -2713,7 +2718,6 @@ static void flush_plug_list(struct blk_plug *plug)
spin_unlock(q->queue_lock);
}
- BUG_ON(!list_empty(&plug->list));
local_irq_restore(flags);
}