From bf0beec0607db3c6f6fb7bd2c6d503792b05cf3f Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Fri, 29 May 2020 15:53:15 +0200 Subject: blk-mq: drain I/O when all CPUs in a hctx are offline Most of blk-mq drivers depend on managed IRQ's auto-affinity to setup up queue mapping. Thomas mentioned the following point[1]: "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." However, current blk-mq implementation doesn't quiesce hw queue before the last CPU in the hctx is shutdown. Even worse, CPUHP_BLK_MQ_DEAD is a cpuhp state handled after the CPU is down, so there isn't any chance to quiesce the hctx before shutting down the CPU. Add new CPUHP_AP_BLK_MQ_ONLINE state to stop allocating from blk-mq hctxs where the last CPU goes away, and wait for completion of in-flight requests. This guarantees that there is no inflight I/O before shutting down the managed IRQ. Add a BLK_MQ_F_STACKING and set it for dm-rq and loop, so we don't need to wait for completion of in-flight requests from these drivers to avoid a potential dead-lock. It is safe to do this for stacking drivers as those do not use interrupts at all and their I/O completions are triggered by underlying devices I/O completion. [1] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@nanos.tec.linutronix.de/ [hch: different retry mechanism, merged two patches, minor cleanups] Signed-off-by: Ming Lei Signed-off-by: Christoph Hellwig Reviewed-by: Hannes Reinecke Reviewed-by: Daniel Wagner Signed-off-by: Jens Axboe --- block/blk-mq-debugfs.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'block/blk-mq-debugfs.c') diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c index 96b7a35c898a..15df3a36e9fa 100644 --- a/block/blk-mq-debugfs.c +++ b/block/blk-mq-debugfs.c @@ -213,6 +213,7 @@ static const char *const hctx_state_name[] = { HCTX_STATE_NAME(STOPPED), HCTX_STATE_NAME(TAG_ACTIVE), HCTX_STATE_NAME(SCHED_RESTART), + HCTX_STATE_NAME(INACTIVE), }; #undef HCTX_STATE_NAME @@ -239,6 +240,7 @@ static const char *const hctx_flag_name[] = { HCTX_FLAG_NAME(TAG_SHARED), HCTX_FLAG_NAME(BLOCKING), HCTX_FLAG_NAME(NO_SCHED), + HCTX_FLAG_NAME(STACKING), }; #undef HCTX_FLAG_NAME -- cgit