[PATCH v2 for-5.8-rc 2/6] nvme-multipath: fix deadlock between ana_work and scan_work

[Sagi Grimberg]

From: Anton Eidelman <anton at lightbitslabs.com>

When scan_work calls nvme_mpath_add_disk() this holds ana_lock
and invokes nvme_parse_ana_log(), which may issue IO
in device_add_disk() and hang waiting for an accessible path.
While nvme_mpath_set_live() only called when nvme_state_is_live(),
a transition may cause NVME_SC_ANA_TRANSITION and requeue the IO.

In order to recover and complete the IO ana_work on the same ctrl
should be able to update the path state and remove NVME_NS_ANA_PENDING.

The deadlock occurs because scan_work keeps holding ana_lock,
so ana_work hangs [1].

Fix:
Now nvme_mpath_add_disk() uses nvme_parse_ana_log() to obtain a copy
of the ANA group desc, and then calls nvme_update_ns_ana_state() without
holding ana_lock.

[1]:
kernel: Workqueue: nvme-wq nvme_scan_work [nvme_core]
kernel: Call Trace:
kernel:  __schedule+0x2b9/0x6c0
kernel:  schedule+0x42/0xb0
kernel:  io_schedule+0x16/0x40
kernel:  do_read_cache_page+0x438/0x830
kernel:  read_cache_page+0x12/0x20
kernel:  read_dev_sector+0x27/0xc0
kernel:  read_lba+0xc1/0x220
kernel:  efi_partition+0x1e6/0x708
kernel:  check_partition+0x154/0x244
kernel:  rescan_partitions+0xae/0x280
kernel:  __blkdev_get+0x40f/0x560
kernel:  blkdev_get+0x3d/0x140
kernel:  __device_add_disk+0x388/0x480
kernel:  device_add_disk+0x13/0x20
kernel:  nvme_mpath_set_live+0x119/0x140 [nvme_core]
kernel:  nvme_update_ns_ana_state+0x5c/0x60 [nvme_core]
kernel:  nvme_set_ns_ana_state+0x1e/0x30 [nvme_core]
kernel:  nvme_parse_ana_log+0xa1/0x180 [nvme_core]
kernel:  nvme_mpath_add_disk+0x47/0x90 [nvme_core]
kernel:  nvme_validate_ns+0x396/0x940 [nvme_core]
kernel:  nvme_scan_work+0x24f/0x380 [nvme_core]
kernel:  process_one_work+0x1db/0x380
kernel:  worker_thread+0x249/0x400
kernel:  kthread+0x104/0x140

kernel: Workqueue: nvme-wq nvme_ana_work [nvme_core]
kernel: Call Trace:
kernel:  __schedule+0x2b9/0x6c0
kernel:  schedule+0x42/0xb0
kernel:  schedule_preempt_disabled+0xe/0x10
kernel:  __mutex_lock.isra.0+0x182/0x4f0
kernel:  ? __switch_to_asm+0x34/0x70
kernel:  ? select_task_rq_fair+0x1aa/0x5c0
kernel:  ? kvm_sched_clock_read+0x11/0x20
kernel:  ? sched_clock+0x9/0x10
kernel:  __mutex_lock_slowpath+0x13/0x20
kernel:  mutex_lock+0x2e/0x40
kernel:  nvme_read_ana_log+0x3a/0x100 [nvme_core]
kernel:  nvme_ana_work+0x15/0x20 [nvme_core]
kernel:  process_one_work+0x1db/0x380
kernel:  worker_thread+0x4d/0x400
kernel:  kthread+0x104/0x140
kernel:  ? process_one_work+0x380/0x380
kernel:  ? kthread_park+0x80/0x80
kernel:  ret_from_fork+0x35/0x40

Fixes: 0d0b660f214d ("nvme: add ANA support")
Signed-off-by: Anton Eidelman <anton at lightbitslabs.com>
Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
---
 drivers/nvme/host/multipath.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index da78e499947a..a646f9eb2e73 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -640,13 +640,13 @@ static ssize_t ana_state_show(struct device *dev, struct device_attribute *attr,
 }
 DEVICE_ATTR_RO(ana_state);
 
-static int nvme_set_ns_ana_state(struct nvme_ctrl *ctrl,
+static int nvme_get_ns_ana_state(struct nvme_ctrl *ctrl,
 		struct nvme_ana_group_desc *desc, void *data)
 {
-	struct nvme_ns *ns = data;
+	struct nvme_ana_group_desc *dst = data;
 
-	if (ns->ana_grpid == le32_to_cpu(desc->grpid)) {
-		nvme_update_ns_ana_state(desc, ns);
+	if (desc->grpid == dst->grpid) {
+		*dst = *desc;
 		return -ENXIO; /* just break out of the loop */
 	}
 
@@ -656,10 +656,19 @@ static int nvme_set_ns_ana_state(struct nvme_ctrl *ctrl,
 void nvme_mpath_add_disk(struct nvme_ns *ns, struct nvme_id_ns *id)
 {
 	if (nvme_ctrl_use_ana(ns->ctrl)) {
+		struct nvme_ana_group_desc desc = {
+			.grpid = id->anagrpid,
+			.state = 0,
+		};
+
 		mutex_lock(&ns->ctrl->ana_lock);
 		ns->ana_grpid = le32_to_cpu(id->anagrpid);
-		nvme_parse_ana_log(ns->ctrl, ns, nvme_set_ns_ana_state);
+		nvme_parse_ana_log(ns->ctrl, &desc, nvme_get_ns_ana_state);
 		mutex_unlock(&ns->ctrl->ana_lock);
+		if (desc.state) {
+			/* found the group desc: update */
+			nvme_update_ns_ana_state(&desc, ns);
+		}
 	} else {
 		mutex_lock(&ns->head->lock);
 		ns->ana_state = NVME_ANA_OPTIMIZED; 
-- 
2.25.1