From: Baolin Wang <baolin.wang@linux.alibaba.com> mainline inclusion from mainline-v5.11-rc6 commit 6c635caef410aa757befbd8857c1eadde5cc22ed category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/ICSIDZ Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... ------------------ On !PREEMPT kernel, we can get below softlockup when doing stress testing with creating and destroying block cgroup repeatly. The reason is it may take a long time to acquire the queue's lock in the loop of blkcg_destroy_blkgs(), or the system can accumulate a huge number of blkgs in pathological cases. We can add a need_resched() check on each loop and release locks and do cond_resched() if true to avoid this issue, since the blkcg_destroy_blkgs() is not called from atomic contexts. [ 4757.010308] watchdog: BUG: soft lockup - CPU#11 stuck for 94s! [ 4757.010698] Call trace: [ 4757.010700]  blkcg_destroy_blkgs+0x68/0x150 [ 4757.010701]  cgwb_release_workfn+0x104/0x158 [ 4757.010702]  process_one_work+0x1bc/0x3f0 [ 4757.010704]  worker_thread+0x164/0x468 [ 4757.010705]  kthread+0x108/0x138 Suggested-by: Tejun Heo <tj@kernel.org> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Conflicts: block/blk-cgroup.c [Due to not merging commit 0d945c1f966b ("block: remove the queue_lock indirection").] Signed-off-by: Zheng Qixing <zhengqixing@huawei.com> --- block/blk-cgroup.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index c0187bf00f71..e10228ffa61f 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1142,6 +1142,8 @@ static void blkcg_css_offline(struct cgroup_subsys_state *css) */ void blkcg_destroy_blkgs(struct blkcg *blkcg) { + might_sleep(); + spin_lock_irq(&blkcg->lock); while (!hlist_empty(&blkcg->blkg_list)) { @@ -1149,14 +1151,20 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg) struct blkcg_gq, blkcg_node); struct request_queue *q = blkg->q; - if (spin_trylock(q->queue_lock)) { - blkg_destroy(blkg); - spin_unlock(q->queue_lock); - } else { + if (need_resched() || !spin_trylock(q->queue_lock)) { + /* + * Given that the system can accumulate a huge number + * of blkgs in pathological cases, check to see if we + * need to rescheduling to avoid softlockup. + */ spin_unlock_irq(&blkcg->lock); - cpu_relax(); + cond_resched(); spin_lock_irq(&blkcg->lock); + continue; } + + blkg_destroy(blkg); + spin_unlock(q->queue_lock); } spin_unlock_irq(&blkcg->lock); -- 2.39.2