Re: [PATCH 3/4] nvmet: fix hang in nvmet_ns_disable()

Sagi Grimberg
2023-01-03T11:14:51Z

On 1/3/23 12:03, Taehee Yoo wrote:
> nvme target namespace is enabled or disabled by nvmet_ns_enable() or
> nvmet_ns_disable().
> The subsys->lock is used to disallow to use namespace data while
> nvmet_ns_enable() or nvmet_ns_disable() are working.
> The ns->enabled boolean variable prevents using namespace data in wrong
> state such as uninitialized state.
>
> nvmet_ns_disable() acquires ns->lock and set ns->enabled false.
> Then, it releases ns->lock for a while to wait ns->disable_done completion.
> At this point, nvmet_ns_enable() can be worked concurrently and it calls
> percpu_ref_init().
> So, ns->disable_done will never be completed.
> Therefore hang would occur at this point.
>
> CPU0 CPU1
> nvmet_ns_disable();
> mutex_lock(&subsys->lock); nvmet_ns_enable();
> mutex_lock(&subsys->lock);
> ns->enabled = false;
> mutex_unlock(&subsys->lock);
> percpu_ref_init();
> wait_for_completion(&ns->disable_done); <-- infinite wait
>
> mutex_lock(&subsys->lock);
> mutex_unlock(&subsys->lock);
>
> INFO: task bash:926 blocked for more than 30 seconds.
> Tainted: G W 6.1.0+ #17
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:bash state:D stack:27200 pid:926 ppid:911
> flags:0x00004000
> Call Trace:
> <TASK>
> __schedule+0xafc/0x2930
> ? io_schedule_timeout+0x160/0x160
> ? _raw_spin_unlock_irq+0x24/0x50
> ? __wait_for_common+0x39b/0x5c0
> ? usleep_range_state+0x190/0x190
> schedule+0x130/0x230
> schedule_timeout+0x18a/0x240
> ? usleep_range_state+0x190/0x190
> ? rcu_read_lock_sched_held+0x12/0x80
> ? lock_downgrade+0x700/0x700
> ? do_raw_spin_trylock+0xb5/0x180
> ? lock_contended+0xdf0/0xdf0
> ? _raw_spin_unlock_irq+0x24/0x50
> ? trace_hardirqs_on+0x3c/0x190
> __wait_for_common+0x1ca/0x5c0
> ? usleep_range_state+0x190/0x190
> ? bit_wait_io+0xf0/0xf0
> ? _raw_spin_unlock_irqrestore+0x59/0x70
> nvmet_ns_disable+0x288/0x490
> ? nvmet_ns_enable+0x970/0x970
> ? lockdep_hardirqs_on_prepare+0x410/0x410
> ? rcu_read_lock_sched_held+0x12/0x80
> ? configfs_write_iter+0x1df/0x480
> ? nvmet_ns_revalidate_size_store+0x220/0x220
> nvmet_ns_enable_store+0x85/0xe0
> [ ... ]
>
> Fixes: a07b4970f464 ("nvmet: add a generic NVMe target")
> Signed-off-by: Taehee Yoo <ap420073@gmail.com>
> ---
> drivers/nvme/target/configfs.c | 14 +++++++-------
> drivers/nvme/target/core.c | 10 ++++++----
> drivers/nvme/target/nvmet.h | 8 +++++++-
> 3 files changed, 20 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
> index 907143870da5..d878c4231d65 100644
> --- a/drivers/nvme/target/configfs.c
> +++ b/drivers/nvme/target/configfs.c
> @@ -348,7 +348,7 @@ static ssize_t nvmet_ns_device_path_store(struct config_item *item,
>
> mutex_lock(&subsys->lock);
> ret = -EBUSY;
> - if (ns->enabled)
> + if (ns->state != NVMET_NS_DISABLED)
> goto out_unlock;
>
> ret = -EINVAL;
> @@ -390,7 +390,7 @@ static ssize_t nvmet_ns_p2pmem_store(struct config_item *item,
> int error;
>
> mutex_lock(&ns->subsys->lock);
> - if (ns->enabled) {
> + if (ns->state != NVMET_NS_DISABLED) {
> ret = -EBUSY;
> goto out_unlock;
> }
> @@ -427,7 +427,7 @@ static ssize_t nvmet_ns_device_uuid_store(struct config_item *item,
> int ret = 0;
>
> mutex_lock(&subsys->lock);
> - if (ns->enabled) {
> + if (ns->state != NVMET_NS_DISABLED) {
> ret = -EBUSY;
> goto out_unlock;
> }
> @@ -458,7 +458,7 @@ static ssize_t nvmet_ns_device_nguid_store(struct config_item *item,
> int ret = 0;
>
> mutex_lock(&subsys->lock);
> - if (ns->enabled) {
> + if (ns->state != NVMET_NS_DISABLED) {
> ret = -EBUSY;
> goto out_unlock;
> }
> @@ -523,7 +523,7 @@ CONFIGFS_ATTR(nvmet_ns_, ana_grpid);
>
> static ssize_t nvmet_ns_enable_show(struct config_item *item, char *page)
> {
> - return sprintf(page, "%d\n", to_nvmet_ns(item)->enabled);
> + return sprintf(page, "%d\n", !!to_nvmet_ns(item)->state);
> }
>
> static ssize_t nvmet_ns_enable_store(struct config_item *item,
> @@ -561,7 +561,7 @@ static ssize_t nvmet_ns_buffered_io_store(struct config_item *item,
> return -EINVAL;
>
> mutex_lock(&ns->subsys->lock);
> - if (ns->enabled) {
> + if (ns->state != NVMET_NS_DISABLED) {
> pr_err("disable ns before setting buffered_io value.\n");
> mutex_unlock(&ns->subsys->lock);
> return -EINVAL;
> @@ -587,7 +587,7 @@ static ssize_t nvmet_ns_revalidate_size_store(struct config_item *item,
> return -EINVAL;
>
> mutex_lock(&ns->subsys->lock);
> - if (!ns->enabled) {
> + if (ns->state != NVMET_NS_ENABLED) {
> pr_err("enable ns before revalidate.\n");
> mutex_unlock(&ns->subsys->lock);
> return -EINVAL;
> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index f66ed13d7c11..58a91fb9c2f7 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -563,7 +563,7 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
> goto out_unlock;
> }
>
> - if (ns->enabled)
> + if (ns->state != NVMET_NS_DISABLED)
> goto out_unlock;
>
> ret = -EMFILE;
> @@ -598,7 +598,7 @@ int nvmet_ns_enable(struct nvmet_ns *ns)
> subsys->nr_namespaces++;
>
> nvmet_ns_changed(subsys, ns->nsid);
> - ns->enabled = true;
> + ns->state = NVMET_NS_ENABLED;
> ret = 0;
> out_unlock:
> mutex_unlock(&subsys->lock);
> @@ -621,10 +621,10 @@ void nvmet_ns_disable(struct nvmet_ns *ns)
> struct nvmet_ctrl *ctrl;
>
> mutex_lock(&subsys->lock);
> - if (!ns->enabled)
> + if (ns->state != NVMET_NS_ENABLED)
> goto out_unlock;
>
> - ns->enabled = false;
> + ns->state = NVMET_NS_DISABLING;
> xa_erase(&ns->subsys->namespaces, ns->nsid);
> if (ns->nsid == subsys->max_nsid)
> subsys->max_nsid = nvmet_max_nsid(subsys);
> @@ -652,6 +652,7 @@ void nvmet_ns_disable(struct nvmet_ns *ns)
> subsys->nr_namespaces--;
> nvmet_ns_changed(subsys, ns->nsid);
> nvmet_ns_dev_disable(ns);
> + ns->state = NVMET_NS_DISABLED;
> out_unlock:
> mutex_unlock(&subsys->lock);
> }
> @@ -689,6 +690,7 @@ struct nvmet_ns *nvmet_ns_alloc(struct nvmet_subsys *subsys, u32 nsid)
> uuid_gen(&ns->uuid);
> ns->buffered_io = false;
> ns->csi = NVME_CSI_NVM;
> + ns->state = NVMET_NS_DISABLED;
>
> return ns;
> }
> diff --git a/drivers/nvme/target/nvmet.h b/drivers/nvme/target/nvmet.h
> index 89bedfcd974c..e609787577c6 100644
> --- a/drivers/nvme/target/nvmet.h
> +++ b/drivers/nvme/target/nvmet.h
> @@ -56,6 +56,12 @@
> #define IPO_IATTR_CONNECT_SQE(x) \
> (cpu_to_le32(offsetof(struct nvmf_connect_command, x)))
>
> +enum nvmet_ns_state {
> + NVMET_NS_ENABLED,
> + NVMET_NS_DISABLING,
> + NVMET_NS_DISABLED
> +};
> +
> struct nvmet_ns {
> struct percpu_ref ref;
> struct block_device *bdev;
> @@ -69,7 +75,7 @@ struct nvmet_ns {
> u32 anagrpid;
>
> bool buffered_io;
> - bool enabled;
> + enum nvmet_ns_state state;
> struct nvmet_subsys *subsys;
> const char *device_path;
>

This looks reasonable to me...
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>