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Message-Id: <8e8a0c4644d5eb01b7f79ec9b67c2b240f4a6434.1611798287.git.baolin.wang@linux.alibaba.com>
Date: Thu, 28 Jan 2021 11:22:00 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: axboe@...nel.dk, tj@...nel.org
Cc: joseph.qi@...ux.alibaba.com, baolin.wang@...ux.alibaba.com,
linux-block@...r.kernel.org, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH v2] blk-cgroup: Use cond_resched() when destroy blkgs
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@...nel.org>
Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
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
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