From f26f97cc41775df83739312fa40db895b67b9923 Mon Sep 17 00:00:00 2001 From: Konstantin Khlebnikov Date: Mon, 8 Jul 2019 18:29:57 +0300 Subject: [PATCH] blk-throttle: fix zero wait time for iops throttled group BugLink: https://bugs.launchpad.net/bugs/1839036 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 Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman Signed-off-by: Kamal Mostafa Signed-off-by: Khalid Elmously --- block/blk-throttle.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index d19f416d6101..df1a741f1a1c 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -892,13 +892,10 @@ static bool tg_with_in_iops_limit(struct throtl_grp *tg, struct bio *bio, unsigned long jiffy_elapsed, jiffy_wait, jiffy_elapsed_rnd; u64 tmp; - jiffy_elapsed = jiffy_elapsed_rnd = 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 = jiffies - tg->slice_start[rw]; - 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 -- 2.39.2