Re: [PATCH] blk-throttle: fix possible io stall when doing upgrade
From: Shaohua Li <shli@kernel.org>
Date: 2017-09-25 17:22:28
On Mon, Sep 25, 2017 at 06:46:42PM +0800, Joseph Qi wrote:
From: Joseph Qi <redacted>
Currently it will try to dispatch bio in throtl_upgrade_state. This may
lead to io stall in the following case.
Say the hierarchy is like:
/-test1
|-subtest1
and subtest1 has 32 queued bios now.
throtl_pending_timer_fn throtl_upgrade_state
------------------------------------------------------------------------
upgrade to max
throtl_select_dispatch
throtl_schedule_next_dispatch
throtl_select_dispatch
throtl_schedule_next_dispatch
Since throtl_select_dispatch will move queued bios from subtest1 to
test1 in throtl_upgrade_state, it will then just do nothing in
throtl_pending_timer_fn. As a result, queued bios won't be dispatched
any more if no proper timer scheduled.Sorry, didn't get it. If throtl_pending_timer_fn does nothing (because throtl_upgrade_state already moves bios to parent), there is no pending blkcg/bio, not rearming the timer wouldn't lose anything. Am I missing anything? could you please describe the failure in details? Thanks, Shaohua
quoted hunk ↗ jump to hunk
Fix this issue by just scheduling dispatch now and let the dispatch be done only in timer. Signed-off-by: Joseph Qi <redacted> --- block/blk-throttle.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-)diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 0fea76a..29d282f 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c@@ -1909,13 +1909,11 @@ static void throtl_upgrade_state(struct throtl_data *td) struct throtl_grp *tg = blkg_to_tg(blkg); struct throtl_service_queue *sq = &tg->service_queue; - tg->disptime = jiffies - 1; - throtl_select_dispatch(sq); - throtl_schedule_next_dispatch(sq, false); + tg->disptime = jiffies; + throtl_schedule_next_dispatch(sq, true); } rcu_read_unlock(); - throtl_select_dispatch(&td->service_queue); - throtl_schedule_next_dispatch(&td->service_queue, false); + throtl_schedule_next_dispatch(&td->service_queue, true); queue_work(kthrotld_workqueue, &td->dispatch_work); }-- 1.9.4