From: Konstantin Khlebnikov khlebnikov@yandex-team.ru
commit 3a10f999ffd464d01c5a05592a15470a3c4bbc36 upstream.
After commit 991f61fe7e1d ("Blk-throttle: reduce tail io latency when iops limit is enforced") wait time could be zero even if group is throttled and cannot issue requests right now. As a result throtl_select_dispatch() turns into busy-loop under irq-safe queue spinlock.
Fix is simple: always round up target time to the next throttle slice.
Fixes: 991f61fe7e1d ("Blk-throttle: reduce tail io latency when iops limit is enforced") Signed-off-by: Konstantin Khlebnikov khlebnikov@yandex-team.ru Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/blk-throttle.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
--- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -892,13 +892,10 @@ static bool tg_with_in_iops_limit(struct unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; u64 tmp;
- jiffy_elapsed = jiffy_elapsed_rnd = jiffies - tg->slice_start[rw]; + jiffy_elapsed = jiffies - tg->slice_start[rw];
- /* Slice has just started. Consider one slice interval */ - if (!jiffy_elapsed) - jiffy_elapsed_rnd = tg->td->throtl_slice; - - jiffy_elapsed_rnd = roundup(jiffy_elapsed_rnd, tg->td->throtl_slice); + /* Round up to the next throttle slice, wait time must be nonzero */ + jiffy_elapsed_rnd = roundup(jiffy_elapsed + 1, tg->td->throtl_slice);
/* * jiffy_elapsed_rnd should not be a big value as minimum iops can be