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@xxxxxxxxxx>
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
Changes from v1:
- Add might_sleep() in blkcg_destroy_blkgs().
- Add an explicitly need_resched() check before releasing lock.
- Add some comments.
---
block/blk-cgroup.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3465d6e..94eeed7 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1016,6 +1016,8 @@ 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)) {
@@ -1031,6 +1033,17 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg)
cpu_relax();
spin_lock_irq(&blkcg->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.
+ */
+ if (need_resched()) {
+ spin_unlock_irq(&blkcg->lock);
+ cond_resched();
+ spin_lock_irq(&blkcg->lock);
+ }
}
spin_unlock_irq(&blkcg->lock);
--
1.8.3.1
