APPLIED/cmnt: [SRU B][PATCH v2 0/7] blk-wbt: fix for LP#1810998

Fri Jan 11 14:26:04 UTC 2019

On 1/11/19 12:07 PM, Mauricio Faria de Oliveira wrote:
> BugLink: https://bugs.launchpad.net/bugs/1810998
>
> [Impact]
>
>  * Users may experience cpu hard lockups when performing
>    rigorous writes to NVMe drives.
>
>  * The fix addresses an scheduling issue in the original
>    implementation of wbt/writeback throttling
>
>  * The fix is commit 2887e41b910b ("blk-wbt: Avoid lock
>    contention and thundering herd issue in wbt_wait"),
>    plus its fix commit 38cfb5a45ee0 ("blk-wbt: improve
>    waking of tasks").
>
>  * Plus a few dependency commits for each fix.
>
>  * Backports are trivial: mainly replace rq_wait_inc_below()
>    with the equivalent atomic_inc_below(), and maintain the
>    __wbt_done() signature, both due to the lack of commit
>    a79050434b45 ("blk-rq-qos: refactor out common elements
>    of blk-wbt"), that changes lots of other/unrelated code.
>
> [Test Case]
>
>  * This command has been reported to reproduce the problem:
>
>    $ sudo iozone -R -s 5G -r 1m -S 2048 -i 0 -G -c -o -l 128 -u 128 -t 128
>
>  * It generates stack traces as below in the original kernel,
>    and does not generate them in the modified/patched kernel.
>
>  * The user/reporter verified the test kernel with these patches
>    resolved the problem.
>
>  * The developer verified in 2 systems (4-core and 24-core but
>    no NVMe) for regressions, and no error messages were logged
>    to dmesg.
>
> [Regression Potential]
>
>  * The regression potential is contained within writeback
>    throttling mechanism (block/blk-wbt.*).
>
>  * The commits have been verified for fixes in later commits in
>    linux-next as of 2019-01-08 and all known fix commits are in.
>
> [Other Info]
>
>  * The problem has been introduced with the blk-wbt mechanism,
>    in v4.10-rc1, and the fix commits in v4.19-rc1 and -rc2,
>    so only Bionic and Cosmic needs this.
>
> [Stack Traces]
>
> [ 393.628647] NMI watchdog: Watchdog detected hard LOCKUP on cpu 30
> ...
> [ 393.628704] CPU: 30 PID: 0 Comm: swapper/30 Tainted: P OE 4.15.0-20-generic #21-Ubuntu
> ...
> [ 393.628720] Call Trace:
> [ 393.628721] <IRQ>
> [ 393.628724] enqueue_task_fair+0x6c/0x7f0
> [ 393.628726] ? __update_load_avg_blocked_se.isra.37+0xd1/0x150
> [ 393.628728] ? __update_load_avg_blocked_se.isra.37+0xd1/0x150
> [ 393.628731] activate_task+0x57/0xc0
> [ 393.628735] ? sched_clock+0x9/0x10
> [ 393.628736] ? sched_clock+0x9/0x10
> [ 393.628738] ttwu_do_activate+0x49/0x90
> [ 393.628739] try_to_wake_up+0x1df/0x490
> [ 393.628741] default_wake_function+0x12/0x20
> [ 393.628743] autoremove_wake_function+0x12/0x40
> [ 393.628744] __wake_up_common+0x73/0x130
> [ 393.628745] __wake_up_common_lock+0x80/0xc0
> [ 393.628746] __wake_up+0x13/0x20
> [ 393.628749] __wbt_done.part.21+0xa4/0xb0
> [ 393.628749] wbt_done+0x72/0xa0
> [ 393.628753] blk_mq_free_request+0xca/0x1a0
> [ 393.628755] blk_mq_end_request+0x48/0x90
> [ 393.628760] nvme_complete_rq+0x23/0x120 [nvme_core]
> [ 393.628763] nvme_pci_complete_rq+0x7a/0x130 [nvme]
> [ 393.628764] __blk_mq_complete_request+0xd2/0x140
> [ 393.628766] blk_mq_complete_request+0x18/0x20
> [ 393.628767] nvme_process_cq+0xe1/0x1b0 [nvme]
> [ 393.628768] nvme_irq+0x23/0x50 [nvme]
> [ 393.628772] __handle_irq_event_percpu+0x44/0x1a0
> [ 393.628773] handle_irq_event_percpu+0x32/0x80
> [ 393.628774] handle_irq_event+0x3b/0x60
> [ 393.628778] handle_edge_irq+0x7c/0x190
> [ 393.628779] handle_irq+0x20/0x30
> [ 393.628783] do_IRQ+0x46/0xd0
> [ 393.628784] common_interrupt+0x84/0x84
> [ 393.628785] </IRQ>
> ...
> [ 393.628794] ? cpuidle_enter_state+0x97/0x2f0
> [ 393.628796] cpuidle_enter+0x17/0x20
> [ 393.628797] call_cpuidle+0x23/0x40
> [ 393.628798] do_idle+0x18c/0x1f0
> [ 393.628799] cpu_startup_entry+0x73/0x80
> [ 393.628802] start_secondary+0x1a6/0x200
> [ 393.628804] secondary_startup_64+0xa5/0xb0
> [ 393.628805] Code: ...
>
> [ 405.981597] nvme nvme1: I/O 393 QID 6 timeout, completion polled
>
> [ 435.597209] INFO: rcu_sched detected stalls on CPUs/tasks:
> [ 435.602858] 30-...0: (1 GPs behind) idle=e26/1/0 softirq=6834/6834 fqs=4485
> [ 435.610203] (detected by 8, t=15005 jiffies, g=6396, c=6395, q=146818)
> [ 435.617025] Sending NMI from CPU 8 to CPUs 30:
> [ 435.617029] NMI backtrace for cpu 30
> [ 435.617031] CPU: 30 PID: 0 Comm: swapper/30 Tainted: P OE 4.15.0-20-generic #21-Ubuntu
> ...
> [ 435.617047] Call Trace:
> [ 435.617048] <IRQ>
> [ 435.617051] enqueue_entity+0x9f/0x6b0
> [ 435.617053] enqueue_task_fair+0x6c/0x7f0
> [ 435.617056] activate_task+0x57/0xc0
> [ 435.617059] ? sched_clock+0x9/0x10
> [ 435.617060] ? sched_clock+0x9/0x10
> [ 435.617061] ttwu_do_activate+0x49/0x90
> [ 435.617063] try_to_wake_up+0x1df/0x490
> [ 435.617065] default_wake_function+0x12/0x20
> [ 435.617067] autoremove_wake_function+0x12/0x40
> [ 435.617068] __wake_up_common+0x73/0x130
> [ 435.617069] __wake_up_common_lock+0x80/0xc0
> [ 435.617070] __wake_up+0x13/0x20
> [ 435.617073] __wbt_done.part.21+0xa4/0xb0
> [ 435.617074] wbt_done+0x72/0xa0
> [ 435.617077] blk_mq_free_request+0xca/0x1a0
> [ 435.617079] blk_mq_end_request+0x48/0x90
> [ 435.617084] nvme_complete_rq+0x23/0x120 [nvme_core]
> [ 435.617087] nvme_pci_complete_rq+0x7a/0x130 [nvme]
> [ 435.617088] __blk_mq_complete_request+0xd2/0x140
> [ 435.617090] blk_mq_complete_request+0x18/0x20
> [ 435.617091] nvme_process_cq+0xe1/0x1b0 [nvme]
> [ 435.617093] nvme_irq+0x23/0x50 [nvme]
> [ 435.617096] __handle_irq_event_percpu+0x44/0x1a0
> [ 435.617097] handle_irq_event_percpu+0x32/0x80
> [ 435.617098] handle_irq_event+0x3b/0x60
> [ 435.617101] handle_edge_irq+0x7c/0x190
> [ 435.617102] handle_irq+0x20/0x30
> [ 435.617106] do_IRQ+0x46/0xd0
> [ 435.617107] common_interrupt+0x84/0x84
> [ 435.617108] </IRQ>
> ...
> [ 435.617117] ? cpuidle_enter_state+0x97/0x2f0
> [ 435.617118] cpuidle_enter+0x17/0x20
> [ 435.617119] call_cpuidle+0x23/0x40
> [ 435.617121] do_idle+0x18c/0x1f0
> [ 435.617122] cpu_startup_entry+0x73/0x80
> [ 435.617125] start_secondary+0x1a6/0x200
> [ 435.617127] secondary_startup_64+0xa5/0xb0
> [ 435.617128] Code: ...
>
> Anchal Agarwal (1):
>   blk-wbt: Avoid lock contention and thundering herd issue in wbt_wait
>
> Jens Axboe (6):
>   blk-wbt: pass in enum wbt_flags to get_rq_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
>
>  block/blk-wbt.c | 130 +++++++++++++++++++++++++++++++++---------------
>  block/blk-wbt.h |   4 +-
>  2 files changed, 92 insertions(+), 42 deletions(-)
>
Applied to bionic/master-next branch, with a fix for the provenance
string on patch 1/7.

Thanks,
Kleber