Our test reported the following stack, and vmcore showed that ->inflight counter is -1. [ffffc9003fcc38d0] __schedule at ffffffff8173d95d [ffffc9003fcc3958] schedule at ffffffff8173de26 [ffffc9003fcc3970] io_schedule at ffffffff810bb6b6 [ffffc9003fcc3988] blkcg_iolatency_throttle at ffffffff813911cb [ffffc9003fcc3a20] rq_qos_throttle at ffffffff813847f3 [ffffc9003fcc3a48] blk_mq_make_request at ffffffff8137468a [ffffc9003fcc3b08] generic_make_request at ffffffff81368b49 [ffffc9003fcc3b68] submit_bio at ffffffff81368d7d [ffffc9003fcc3bb8] ext4_io_submit at ffffffffa031be00 [ext4] [ffffc9003fcc3c00] ext4_writepages at ffffffffa03163de [ext4] [ffffc9003fcc3d68] do_writepages at ffffffff811c49ae [ffffc9003fcc3d78] __filemap_fdatawrite_range at ffffffff811b6188 [ffffc9003fcc3e30] filemap_write_and_wait_range at ffffffff811b6301 [ffffc9003fcc3e60] ext4_sync_file at ffffffffa030cee8 [ext4] [ffffc9003fcc3ea8] vfs_fsync_range at ffffffff8128594b [ffffc9003fcc3ee8] do_fsync at ffffffff81285abd [ffffc9003fcc3f18] sys_fsync at ffffffff81285d50 [ffffc9003fcc3f28] do_syscall_64 at ffffffff81003c04 [ffffc9003fcc3f50] entry_SYSCALL_64_after_swapgs at ffffffff81742b8e The ->inflight counter may be negative (-1) if 0) blk-throttle had been enabled when the IO was issued, so its bio has a associated blkg, 1) blk-iolatency was disabled when the IO was issued, so iolatency_grp in this blkg was not available by then, 2) blk-iolatency was enabled before this IO reached its endio, so that iolatency_grp became available when the IO did the endio. 3) the ->inflight counter is decreased from 0 to -1. This uses atomic_dec_is_positive() instead to avoid the negative inflight counter. Signed-off-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx> --- block/blk-iolatency.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index 159af76d60e6..da4ede5c5ddf 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -660,7 +660,12 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio) } rqw = &iolat->rq_wait; - atomic_dec(&rqw->inflight); + /* + * if blkg is enabled by another throttler (e.g. blk-throttle) + * and blk-iolatency is enabled while IO is inflight, + * blk-iolatency's ->inflight counter may be still 0. + */ + atomic_dec_if_positive(&rqw->inflight); if (!enabled || iolat->min_lat_nsec == 0) goto next; iolatency_record_time(iolat, &bio->bi_issue, now, @@ -692,7 +697,8 @@ static void blkcg_iolatency_cleanup(struct rq_qos *rqos, struct bio *bio) goto next; rqw = &iolat->rq_wait; - atomic_dec(&rqw->inflight); + /* see comments in blkcg_iolatency_done_io() */ + atomic_dec_if_positive(&rqw->inflight); wake_up(&rqw->wait); next: blkg = blkg->parent; -- 2.20.1.2.gb21ebb6
