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
one cpuhp state handled after the CPU is down, so there isn't any chance
to quiesce hctx for blk-mq wrt. CPU hotplug.
Add new cpuhp state of CPUHP_AP_BLK_MQ_ONLINE for blk-mq to stop queues
and wait for completion of in-flight requests.
We will stop hw queue and wait for completion of in-flight requests
when one hctx is becoming dead in the following patch. This way may
cause dead-lock for some stacking blk-mq drivers, such as dm-rq and
loop.
Add blk-mq flag of BLK_MQ_F_NO_MANAGED_IRQ and mark it for dm-rq and
loop, so we needn't to wait for completion of in-flight requests from
dm-rq & loop, then the potential dead-lock can be avoided.
[1] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@xxxxxxxxxxxxxxxxxxxxxxx/
Cc: John Garry <john.garry@xxxxxxxxxx>
Cc: Bart Van Assche <bvanassche@xxxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
block/blk-mq-debugfs.c | 1 +
block/blk-mq.c | 19 +++++++++++++++++++
drivers/block/loop.c | 2 +-
drivers/md/dm-rq.c | 2 +-
include/linux/blk-mq.h | 3 +++
include/linux/cpuhotplug.h | 1 +
6 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index b3f2ba483992..8e745826eb86 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -239,6 +239,7 @@ static const char *const hctx_flag_name[] = {
HCTX_FLAG_NAME(TAG_SHARED),
HCTX_FLAG_NAME(BLOCKING),
HCTX_FLAG_NAME(NO_SCHED),
+ HCTX_FLAG_NAME(NO_MANAGED_IRQ),
};
#undef HCTX_FLAG_NAME
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 65f0aaed55ff..d432cc74ef78 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2261,6 +2261,16 @@ int blk_mq_alloc_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
return -ENOMEM;
}
+static int blk_mq_hctx_notify_online(unsigned int cpu, struct hlist_node *node)
+{
+ return 0;
+}
+
+static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
+{
+ return 0;
+}
+
/*
* 'cpu' is going away. splice any existing rq_list entries from this
* software queue to the hw queue dispatch list, and ensure that it
@@ -2297,6 +2307,9 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
static void blk_mq_remove_cpuhp(struct blk_mq_hw_ctx *hctx)
{
+ if (!(hctx->flags & BLK_MQ_F_NO_MANAGED_IRQ))
+ cpuhp_state_remove_instance_nocalls(CPUHP_AP_BLK_MQ_ONLINE,
+ &hctx->cpuhp_online);
cpuhp_state_remove_instance_nocalls(CPUHP_BLK_MQ_DEAD,
&hctx->cpuhp_dead);
}
@@ -2356,6 +2369,9 @@ static int blk_mq_init_hctx(struct request_queue *q,
{
hctx->queue_num = hctx_idx;
+ if (!(hctx->flags & BLK_MQ_F_NO_MANAGED_IRQ))
+ cpuhp_state_add_instance_nocalls(CPUHP_AP_BLK_MQ_ONLINE,
+ &hctx->cpuhp_online);
cpuhp_state_add_instance_nocalls(CPUHP_BLK_MQ_DEAD, &hctx->cpuhp_dead);
hctx->tags = set->tags[hctx_idx];
@@ -3610,6 +3626,9 @@ static int __init blk_mq_init(void)
{
cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
blk_mq_hctx_notify_dead);
+ cpuhp_setup_state_multi(CPUHP_AP_BLK_MQ_ONLINE, "block/mq:online",
+ blk_mq_hctx_notify_online,
+ blk_mq_hctx_notify_offline);
return 0;
}
subsys_initcall(blk_mq_init);
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index da693e6a834e..784f2e038b55 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2037,7 +2037,7 @@ static int loop_add(struct loop_device **l, int i)
lo->tag_set.queue_depth = 128;
lo->tag_set.numa_node = NUMA_NO_NODE;
lo->tag_set.cmd_size = sizeof(struct loop_cmd);
- lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE;
+ lo->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;
lo->tag_set.driver_data = lo;
err = blk_mq_alloc_tag_set(&lo->tag_set);
diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 3f8577e2c13b..5f1ff70ac029 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -547,7 +547,7 @@ int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)
md->tag_set->ops = &dm_mq_ops;
md->tag_set->queue_depth = dm_get_blk_mq_queue_depth();
md->tag_set->numa_node = md->numa_node_id;
- md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
+ md->tag_set->flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_NO_MANAGED_IRQ;
md->tag_set->nr_hw_queues = dm_get_blk_mq_nr_hw_queues();
md->tag_set->driver_data = md;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index b45148ba3291..f550b5274b8b 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 +393,7 @@ struct blk_mq_ops {
enum {
BLK_MQ_F_SHOULD_MERGE = 1 << 0,
BLK_MQ_F_TAG_SHARED = 1 << 1,
+ BLK_MQ_F_NO_MANAGED_IRQ = 1 << 2,
BLK_MQ_F_BLOCKING = 1 << 5,
BLK_MQ_F_NO_SCHED = 1 << 6,
BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 77d70b633531..24b3a77810b6 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -152,6 +152,7 @@ enum cpuhp_state {
CPUHP_AP_SMPBOOT_THREADS,
CPUHP_AP_X86_VDSO_VMA_ONLINE,
CPUHP_AP_IRQ_AFFINITY_ONLINE,
+ CPUHP_AP_BLK_MQ_ONLINE,
CPUHP_AP_ARM_MVEBU_SYNC_CLOCKS,
CPUHP_AP_X86_INTEL_EPB_ONLINE,
CPUHP_AP_PERF_ONLINE,
