[PATCH AUTOSEL 6.6 34/47] nvme: fix deadlock between reset and scan

Sasha Levin
2023-12-11T13:54:57Z

From: Bitao Hu <yaoma@linux.alibaba.com>

[ Upstream commit 839a40d1e730977d4448d141fa653517c2959a88 ]

If controller reset occurs when allocating namespace, both
nvme_reset_work and nvme_scan_work will hang, as shown below.

Test Scripts:

for ((t=1;t<=128;t++))
do
nsid=`nvme create-ns /dev/nvme1 -s 14537724 -c 14537724 -f 0 -m 0 \
-d 0 | awk -F: '{print($NF);}'`
nvme attach-ns /dev/nvme1 -n $nsid -c 0
done
nvme reset /dev/nvme1

We will find that both nvme_reset_work and nvme_scan_work hung:

INFO: task kworker/u249:4:17848 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
task:kworker/u249:4 state:D stack: 0 pid:17848 ppid: 2
flags:0x00000028
Workqueue: nvme-reset-wq nvme_reset_work [nvme]
Call trace:
__switch_to+0xb4/0xfc
__schedule+0x22c/0x670
schedule+0x4c/0xd0
blk_mq_freeze_queue_wait+0x84/0xc0
nvme_wait_freeze+0x40/0x64 [nvme_core]
nvme_reset_work+0x1c0/0x5cc [nvme]
process_one_work+0x1d8/0x4b0
worker_thread+0x230/0x440
kthread+0x114/0x120
INFO: task kworker/u249:3:22404 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
task:kworker/u249:3 state:D stack: 0 pid:22404 ppid: 2
flags:0x00000028
Workqueue: nvme-wq nvme_scan_work [nvme_core]
Call trace:
__switch_to+0xb4/0xfc
__schedule+0x22c/0x670
schedule+0x4c/0xd0
rwsem_down_write_slowpath+0x32c/0x98c
down_write+0x70/0x80
nvme_alloc_ns+0x1ac/0x38c [nvme_core]
nvme_validate_or_alloc_ns+0xbc/0x150 [nvme_core]
nvme_scan_ns_list+0xe8/0x2e4 [nvme_core]
nvme_scan_work+0x60/0x500 [nvme_core]
process_one_work+0x1d8/0x4b0
worker_thread+0x260/0x440
kthread+0x114/0x120
INFO: task nvme:28428 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
task:nvme state:D stack: 0 pid:28428 ppid: 27119
flags:0x00000000
Call trace:
__switch_to+0xb4/0xfc
__schedule+0x22c/0x670
schedule+0x4c/0xd0
schedule_timeout+0x160/0x194
do_wait_for_common+0xac/0x1d0
__wait_for_common+0x78/0x100
wait_for_completion+0x24/0x30
__flush_work.isra.0+0x74/0x90
flush_work+0x14/0x20
nvme_reset_ctrl_sync+0x50/0x74 [nvme_core]
nvme_dev_ioctl+0x1b0/0x250 [nvme_core]
__arm64_sys_ioctl+0xa8/0xf0
el0_svc_common+0x88/0x234
do_el0_svc+0x7c/0x90
el0_svc+0x1c/0x30
el0_sync_handler+0xa8/0xb0
el0_sync+0x148/0x180

The reason for the hang is that nvme_reset_work occurs while nvme_scan_work
is still running. nvme_scan_work may add new ns into ctrl->namespaces
list after nvme_reset_work frozen all ns->q in ctrl->namespaces list.
The newly added ns is not frozen, so nvme_wait_freeze will wait forever.
Unfortunately, ctrl->namespaces_rwsem is held by nvme_reset_work, so
nvme_scan_work will also wait forever. Now we are deadlocked!

PROCESS1 PROCESS2
============== ==============
nvme_scan_work
... nvme_reset_work
nvme_validate_or_alloc_ns nvme_dev_disable
nvme_alloc_ns nvme_start_freeze
down_write ...
nvme_ns_add_to_ctrl_list ...
up_write nvme_wait_freeze
... down_read
nvme_alloc_ns blk_mq_freeze_queue_wait
down_write

Fix by marking the ctrl with say NVME_CTRL_FROZEN flag set in
nvme_start_freeze and cleared in nvme_unfreeze. Then the scan can check
it before adding the new namespace (under the namespaces_rwsem).

Signed-off-by: Bitao Hu <yaoma@linux.alibaba.com>
Reviewed-by: Guixin Liu <kanie@linux.alibaba.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/nvme/host/core.c | 10 ++++++++++
drivers/nvme/host/nvme.h | 1 +
2 files changed, 11 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 4e7bda7749caa..d5bfb6db5a1cc 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3641,6 +3641,14 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
goto out_unlink_ns;

down_write(&ctrl->namespaces_rwsem);
+ /*
+ * Ensure that no namespaces are added to the ctrl list after the queues
+ * are frozen, thereby avoiding a deadlock between scan and reset.
+ */
+ if (test_bit(NVME_CTRL_FROZEN, &ctrl->flags)) {
+ up_write(&ctrl->namespaces_rwsem);
+ goto out_unlink_ns;
+ }
nvme_ns_add_to_ctrl_list(ns);
up_write(&ctrl->namespaces_rwsem);
nvme_get_ctrl(ctrl);
@@ -4550,6 +4558,7 @@ void nvme_unfreeze(struct nvme_ctrl *ctrl)
list_for_each_entry(ns, &ctrl->namespaces, list)
blk_mq_unfreeze_queue(ns->queue);
up_read(&ctrl->namespaces_rwsem);
+ clear_bit(NVME_CTRL_FROZEN, &ctrl->flags);
}
EXPORT_SYMBOL_GPL(nvme_unfreeze);

@@ -4583,6 +4592,7 @@ void nvme_start_freeze(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;

+ set_bit(NVME_CTRL_FROZEN, &ctrl->flags);
down_read(&ctrl->namespaces_rwsem);
list_for_each_entry(ns, &ctrl->namespaces, list)
blk_freeze_queue_start(ns->queue);
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index 68313148e6ed5..bc6d6eabab66b 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -251,6 +251,7 @@ enum nvme_ctrl_flags {
NVME_CTRL_STOPPED = 3,
NVME_CTRL_SKIP_ID_CNS_CS = 4,
NVME_CTRL_DIRTY_CAPABILITY = 5,
+ NVME_CTRL_FROZEN = 6,
};

struct nvme_ctrl {
--
2.42.0