Re: [PATCH v2] blk-cgroup: Use cond_resched() when destroy blkgs
On 1/27/21 8:49 PM, Baolin Wang wrote: > > > 在 2021/1/28 11:41, Jens Axboe 写道: >> On 1/27/21 8:22 PM, Baolin Wang wrote: >>> 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 >> >> Kind of ugly with the two clauses for dropping the blkcg lock, one >> being a cpu_relax() and the other a resched. How about something >> like this: >> >> >> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c >> index 031114d454a6..4221a1539391 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(>lock); >> >> while (!hlist_empty(>blkg_list)) { >> @@ -1023,14 +1025,20 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg) >> struct blkcg_gq, blkcg_node); >> struct request_queue *q = blkg->q; >> >> -if (spin_trylock(>queue_lock)) { >> -blkg_destroy(blkg); >> -spin_unlock(>queue_lock); >> -} else { >> +if (need_resched() || !spin_trylock(>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(>lock); >> -cpu_relax(); >> +cond_resched(); >> spin_lock_irq(>lock); >> +continue; >> } >> + >> +blkg_destroy(blkg); >> +spin_unlock(>queue_lock); >> } >> >> spin_unlock_irq(>lock); >> > > Looks better to me. Do I need resend with your suggestion? Thanks. Probably best, gives Tejun another chance to sign off on it :-) -- Jens Axboe
Re: [PATCH v2] blk-cgroup: Use cond_resched() when destroy blkgs
On 1/27/21 8:22 PM, Baolin Wang wrote: > 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 Kind of ugly with the two clauses for dropping the blkcg lock, one being a cpu_relax() and the other a resched. How about something like this: diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 031114d454a6..4221a1539391 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(>lock); while (!hlist_empty(>blkg_list)) { @@ -1023,14 +1025,20 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg) struct blkcg_gq, blkcg_node); struct request_queue *q = blkg->q; - if (spin_trylock(>queue_lock)) { - blkg_destroy(blkg); - spin_unlock(>queue_lock); - } else { + if (need_resched() || !spin_trylock(>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(>lock); - cpu_relax(); + cond_resched(); spin_lock_irq(>lock); + continue; } + + blkg_destroy(blkg); + spin_unlock(>queue_lock); } spin_unlock_irq(>lock); -- Jens Axboe
Re: [PATCH v2] blk-cgroup: Use cond_resched() when destroy blkgs
在 2021/1/28 11:41, Jens Axboe 写道: On 1/27/21 8:22 PM, Baolin Wang wrote: 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 Kind of ugly with the two clauses for dropping the blkcg lock, one being a cpu_relax() and the other a resched. How about something like this: diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 031114d454a6..4221a1539391 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(>lock); while (!hlist_empty(>blkg_list)) { @@ -1023,14 +1025,20 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg) struct blkcg_gq, blkcg_node); struct request_queue *q = blkg->q; - if (spin_trylock(>queue_lock)) { - blkg_destroy(blkg); - spin_unlock(>queue_lock); - } else { + if (need_resched() || !spin_trylock(>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(>lock); - cpu_relax(); + cond_resched(); spin_lock_irq(>lock); + continue; } + + blkg_destroy(blkg); + spin_unlock(>queue_lock); } spin_unlock_irq(>lock); Looks better to me. Do I need resend with your suggestion? Thanks.
Re: [PATCH v2] blk-cgroup: Use cond_resched() when destroy blkgs
On Thu, Jan 28, 2021 at 11:22:00AM +0800, Baolin Wang wrote: > 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 > Signed-off-by: Baolin Wang Acked-by: Tejun Heo Thanks. -- tejun
[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 Signed-off-by: Baolin Wang --- 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(>lock); while (!hlist_empty(>blkg_list)) { @@ -1031,6 +1033,17 @@ void blkcg_destroy_blkgs(struct blkcg *blkcg) cpu_relax(); spin_lock_irq(>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(>lock); + cond_resched(); + spin_lock_irq(>lock); + } } spin_unlock_irq(>lock); -- 1.8.3.1