[Devel] [PATCH RHEL7 COMMIT] ms/rq-qos: use a mb for got_token
Konstantin Khorenko
khorenko at virtuozzo.com
Fri Oct 14 19:50:19 MSK 2022
The commit is pushed to "branch-rh7-3.10.0-1160.76.1.vz7.189.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1160.76.1.vz7.189.4
------>
commit 3ae45bd569ebbd263b23e4e5669303bd54ba07e0
Author: Josef Bacik <josef at toxicpanda.com>
Date: Thu Sep 29 14:30:12 2022 +0300
ms/rq-qos: use a mb for got_token
Oleg noticed that our checking of data.got_token is unsafe in the
cleanup case, and should really use a memory barrier. Use a wmb on the
write side, and a rmb() on the read side. We don't need one in the main
loop since we're saved by set_current_state().
Reviewed-by: Oleg Nesterov <oleg at redhat.com>
Signed-off-by: Josef Bacik <josef at toxicpanda.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Changes when porting to vz7:
- original patch is patching block/blk-rq-qos.c:rq_qos_wait, but in vz7
similar hunk is in block/blk-wbt.c:__wbt_wait
- also original patch is patching rq_qos_wake_function, but in vz7
similar hunk is in wbt_wake_function
https://jira.sw.ru/browse/PSBM-141883
(cherry picked from commit ac38297f7038cd5b80d66f8809c7bbf5b70031f3)
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
=================
Patchset description:
blk-wbt: Fix hardlockup in wbt_done()
We have a hard lockup detected in this stack:
#13 [ffff9103fe603af8] __enqueue_entity at ffffffffb8ce64c5
#14 [ffff9103fe603b00] enqueue_entity at ffffffffb8cee27a
#15 [ffff9103fe603b50] enqueue_task_fair at ffffffffb8ceea9c
#16 [ffff9103fe603ba0] activate_task at ffffffffb8cdd029
#17 [ffff9103fe603bc8] ttwu_do_activate at ffffffffb8cdd491
#18 [ffff9103fe603bf0] try_to_wake_up at ffffffffb8ce124a
#19 [ffff9103fe603c40] default_wake_function at ffffffffb8ce1552
#20 [ffff9103fe603c50] autoremove_wake_function at ffffffffb8ccb178
#21 [ffff9103fe603c78] __wake_up_common at ffffffffb8cd7752
#22 [ffff9103fe603cd0] __wake_up_common_lock at ffffffffb8cd7873
#23 [ffff9103fe603d40] __wake_up at ffffffffb8cd78c3
#24 [ffff9103fe603d50] __wbt_done at ffffffffb8fb6573
#25 [ffff9103fe603d60] wbt_done at ffffffffb8fb65f2
#26 [ffff9103fe603d80] __blk_mq_finish_request at ffffffffb8f8daa1
#27 [ffff9103fe603db8] blk_mq_finish_request at ffffffffb8f8db6a
#28 [ffff9103fe603dc8] blk_mq_sched_put_request at ffffffffb8f93ee0
#29 [ffff9103fe603de8] blk_mq_end_request at ffffffffb8f8d1a4
#30 [ffff9103fe603e08] nvme_complete_rq at ffffffffc033dcfc [nvme_core]
#31 [ffff9103fe603e18] nvme_pci_complete_rq at ffffffffc038be70 [nvme]
#32 [ffff9103fe603e40] __blk_mq_complete_request at ffffffffb8f8d316
#33 [ffff9103fe603e68] blk_mq_complete_request at ffffffffb8f8d3c7
#34 [ffff9103fe603e78] nvme_irq at ffffffffc038c0b2 [nvme]
#35 [ffff9103fe603eb0] __handle_irq_event_percpu at ffffffffb8d66bb4
#36 [ffff9103fe603ef8] handle_irq_event_percpu at ffffffffb8d66d62
#37 [ffff9103fe603f28] handle_irq_event at ffffffffb8d66dec
#38 [ffff9103fe603f50] handle_edge_irq at ffffffffb8d69c0f
#39 [ffff9103fe603f70] handle_irq at ffffffffb8c30524
#40 [ffff9103fe603fb8] do_IRQ at ffffffffb93d898d
which is exactly the same as ubuntu problem here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1810998
this is because we have writeback throttling ported which does not work
well in some cases.
In launchpad bug it helped to port these patches from mainstream:
* CPU hard lockup with rigorous writes to NVMe drive (LP: #1810998)
- blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
- blk-wbt: move disable check into get_limit()
- blk-wbt: use wq_has_sleeper() for wq active check
- blk-wbt: fix has-sleeper queueing check
- blk-wbt: abstract out end IO completion handler
- blk-wbt: improve waking of tasks
which fixes similar lockup issues in wbt.
More over I've found some more small and useful patches which fix races
(missed wakeups) in this code, so I've also put them in the patchset.
Anchal Agarwal (1):
blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
Herbert Xu (1):
net: Generalise wq_has_sleeper helper
Jens Axboe (5):
blk-wbt: move disable check into get_limit()
blk-wbt: use wq_has_sleeper() for wq active check
blk-wbt: fix has-sleeper queueing check
blk-wbt: abstract out end IO completion handler
blk-wbt: improve waking of tasks
Josef Bacik (5):
wait: add wq_has_single_sleeper helper
rq-qos: fix missed wake-ups in rq_qos_throttle
rq-qos: don't reset has_sleepers on spurious wakeups
rq-qos: set ourself TASK_UNINTERRUPTIBLE after we schedule
rq-qos: use a mb for got_token
https://jira.sw.ru/browse/PSBM-141883
Ported-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
block/blk-wbt.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 4c5b6899db71..099678cd0d04 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -541,6 +541,7 @@ static int wbt_wake_function(struct __wait_queue *curr, unsigned int mode,
return -1;
data->got_token = true;
+ smp_wmb();
list_del_init(&curr->task_list);
wake_up_process(data->task);
return 1;
@@ -573,6 +574,7 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);
has_sleeper = !wq_has_single_sleeper(&rqw->wait);
do {
+ /* The memory barrier in set_task_state saves us here. */
if (data.got_token)
break;
@@ -585,6 +587,7 @@ static void __wbt_wait(struct rq_wb *rwb, enum wbt_flags wb_acct,
* which means we now have two. Put our local token
* and wake anyone else potentially waiting for one.
*/
+ smp_rmb();
if (data.got_token)
wbt_rqw_done(rwb, rqw, wb_acct);
break;
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