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authorMing Lei <ming.lei@redhat.com>2020-05-29 16:53:15 +0300
committerJens Axboe <axboe@kernel.dk>2020-05-29 19:23:25 +0300
commitbf0beec0607db3c6f6fb7bd2c6d503792b05cf3f (patch)
tree10b8e3b1cc69eb2e8b4f23cc176726c371d2c239 /include/linux/blk-mq.h
parent602380d28e28b454683efac41dc4b2862d055d91 (diff)
downloadlinux-bf0beec0607db3c6f6fb7bd2c6d503792b05cf3f.tar.xz
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 <ming.lei@redhat.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Hannes Reinecke <hare@suse.de> Reviewed-by: Daniel Wagner <dwagner@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'include/linux/blk-mq.h')
-rw-r--r--include/linux/blk-mq.h10
1 files changed, 10 insertions, 0 deletions
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 856bb10993cf..d6fcae17da5a 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -140,6 +140,8 @@ struct blk_mq_hw_ctx {
*/
atomic_t nr_active;
+ /** @cpuhp_online: List to store request if CPU is going to die */
+ struct hlist_node cpuhp_online;
/** @cpuhp_dead: List to store request if some CPU die. */
struct hlist_node cpuhp_dead;
/** @kobj: Kernel object for sysfs. */
@@ -391,6 +393,11 @@ struct blk_mq_ops {
enum {
BLK_MQ_F_SHOULD_MERGE = 1 << 0,
BLK_MQ_F_TAG_SHARED = 1 << 1,
+ /*
+ * Set when this device requires underlying blk-mq device for
+ * completing IO:
+ */
+ BLK_MQ_F_STACKING = 1 << 2,
BLK_MQ_F_BLOCKING = 1 << 5,
BLK_MQ_F_NO_SCHED = 1 << 6,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
@@ -400,6 +407,9 @@ enum {
BLK_MQ_S_TAG_ACTIVE = 1,
BLK_MQ_S_SCHED_RESTART = 2,
+ /* hw queue is inactive after all its CPUs become offline */
+ BLK_MQ_S_INACTIVE = 3,
+
BLK_MQ_MAX_DEPTH = 10240,
BLK_MQ_CPU_WORK_BATCH = 8,