path: root/block
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authorJoseph Qi <qijiang.qj@alibaba-inc.com>2017-09-30 14:38:49 +0800
committerJens Axboe <axboe@kernel.dk>2017-10-03 15:41:55 -0600
commit4f02fb7617ba12ac15d261c654b9759ea8f1f1ef (patch)
tree3fae18c740588451dd337bcbe601cf241d6e5204 /block
parentMAINTAINERS: update list for NBD (diff)
blk-throttle: fix possible io stall when upgrade to max
There is a case which will lead to io stall. The case is described as follows. /test1 |-subtest1 /test2 |-subtest2 And subtest1 and subtest2 each has 32 queued bios already. Now upgrade to max. In throtl_upgrade_state, it will try to dispatch bios as follows: 1) tg=subtest1, do nothing; 2) tg=test1, transfer 32 queued bios from subtest1 to test1; no pending left, no need to schedule next dispatch; 3) tg=subtest2, do nothing; 4) tg=test2, transfer 32 queued bios from subtest2 to test2; no pending left, no need to schedule next dispatch; 5) tg=/, transfer 8 queued bios from test1 to /, 8 queued bios from test2 to /, 8 queued bios from test1 to /, and 8 queued bios from test2 to /; note that test1 and test2 each still has 16 queued bios left; 6) tg=/, try to schedule next dispatch, but since disptime is now (update in tg_update_disptime, wait=0), pending timer is not scheduled in fact; 7) In throtl_upgrade_state it totally dispatches 32 queued bios and with 32 left. test1 and test2 each has 16 queued bios; 8) throtl_pending_timer_fn sees the left over bios, but could do nothing, because throtl_select_dispatch returns 0, and test1/test2 has no pending tg. The blktrace shows the following: 8,32 0 0 2.539007641 0 m N throtl upgrade to max 8,32 0 0 2.539072267 0 m N throtl /test2 dispatch nr_queued=16 read=0 write=16 8,32 7 0 2.539077142 0 m N throtl /test1 dispatch nr_queued=16 read=0 write=16 So force schedule dispatch if there are pending children. Reviewed-by: Shaohua Li <shli@fb.com> Signed-off-by: Joseph Qi <qijiang.qj@alibaba-inc.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block')
1 files changed, 2 insertions, 2 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 0fea76aa0f3f..17816a028dcb 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -1911,11 +1911,11 @@ static void throtl_upgrade_state(struct throtl_data *td)
tg->disptime = jiffies - 1;
- throtl_schedule_next_dispatch(sq, false);
+ throtl_schedule_next_dispatch(sq, true);
- throtl_schedule_next_dispatch(&td->service_queue, false);
+ throtl_schedule_next_dispatch(&td->service_queue, true);
queue_work(kthrotld_workqueue, &td->dispatch_work);