Hi,
Thomas mentioned:
"
That was the constraint of managed interrupts from the very beginning:
The driver/subsystem has to quiesce the interrupt line and the associated
queue _before_ it gets shutdown in CPU unplug and not fiddle with it
until it's restarted by the core when the CPU is plugged in again.
"
But no drivers or blk-mq do that before one hctx becomes dead(all
CPUs for one hctx are offline), and even it is worse, blk-mq stills tries
to run hw queue after hctx is dead, see blk_mq_hctx_notify_dead().
This patchset tries to address the issue by two stages:
1) add one new cpuhp state of CPUHP_AP_BLK_MQ_ONLINE
- mark the hctx as internal stopped, and drain all in-flight requests
if the hctx is going to be dead.
2) re-submit IO in the state of CPUHP_BLK_MQ_DEAD after the hctx becomes dead
- steal bios from the request, and resubmit them via generic_make_request(),
then these IO will be mapped to other live hctx for dispatch
Please comment & review, thanks!
John, I don't add your tested-by tag since V3 have some changes,
and I appreciate if you may run your test on V3.
V3:
- re-organize patch 2 & 3 a bit for addressing Hannes's comment
- fix patch 4 for avoiding potential deadlock, as found by Hannes
V2:
- patch4 & patch 5 in V1 have been merged to block tree, so remove
them
- address comments from John Garry and Minwoo
Ming Lei (5):
blk-mq: add new state of BLK_MQ_S_INTERNAL_STOPPED
blk-mq: prepare for draining IO when hctx's all CPUs are offline
blk-mq: stop to handle IO and drain IO before hctx becomes dead
blk-mq: re-submit IO in case that hctx is dead
blk-mq: handle requests dispatched from IO scheduler in case that hctx
is dead
block/blk-mq-debugfs.c | 2 +
block/blk-mq-tag.c | 2 +-
block/blk-mq-tag.h | 2 +
block/blk-mq.c | 135 +++++++++++++++++++++++++++++++++----
block/blk-mq.h | 3 +-
drivers/block/loop.c | 2 +-
drivers/md/dm-rq.c | 2 +-
include/linux/blk-mq.h | 5 ++
include/linux/cpuhotplug.h | 1 +
9 files changed, 138 insertions(+), 16 deletions(-)
Cc: John Garry <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Keith Busch <[email protected]>
--
2.20.1
