[PATCH] nvme-pci: silence a lockdep complaint
Keith Busch
kbusch at kernel.org
Wed May 22 14:36:19 PDT 2024
On Wed, May 22, 2024 at 09:00:34PM +0300, Sagi Grimberg wrote:
> I don't understand lockdep well enough to do that. This warning
> exists for 6 months now. The conclusion that Keith came to (and I agreed)
> is that it can't happen, because nvme_timeout handler will not disable the
> device while the ctrl reset_work is running, the ctrl state machine will
> prevent that from happening.
>
> There was an attempt to convert namespaces_rwsem a srcu, but my comment to
> that was that this is an intrusive change for a complaint that we think is a
> false-positive.
I'll play devil's advocate and suggest there might be some whacky
timeout_work, scan_work, reset_work, and pciehp irq that could result in
a read, write, wait, read deadlock. I don't think it can happen, but
it's harder to prove that.
The below patch is what I'm messing with. I have a CMIC PCI NVMe and
nvme native multipathing enabled, and that can recreate the lockdep
splat 100% of the time. It goes away with this patch. Non-multipath
devices are harder to hit the lockdep splat for a different reason.
>From 00dd7a573d3dd14be748b46e040bb5eb0f5687b1 Mon Sep 17 00:00:00 2001
From: Keith Busch <kbusch at kernel.org>
Date: Tue, 21 May 2024 06:41:45 -0700
Subject: [PATCH] nvme: switch rwsem to srcu
Signed-off-by: Keith Busch <kbusch at kernel.org>
---
drivers/nvme/host/core.c | 94 +++++++++++++++++++++--------------
drivers/nvme/host/ioctl.c | 12 ++---
drivers/nvme/host/multipath.c | 21 ++++----
drivers/nvme/host/nvme.h | 3 +-
4 files changed, 76 insertions(+), 54 deletions(-)
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 7706df2373494..480af74f1606e 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3684,9 +3684,10 @@ static int nvme_init_ns_head(struct nvme_ns *ns, struct nvme_ns_info *info)
struct nvme_ns *nvme_find_get_ns(struct nvme_ctrl *ctrl, unsigned nsid)
{
struct nvme_ns *ns, *ret = NULL;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list) {
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
if (ns->head->ns_id == nsid) {
if (!nvme_get_ns(ns))
continue;
@@ -3696,7 +3697,7 @@ struct nvme_ns *nvme_find_get_ns(struct nvme_ctrl *ctrl, unsigned nsid)
if (ns->head->ns_id > nsid)
break;
}
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
return ret;
}
EXPORT_SYMBOL_NS_GPL(nvme_find_get_ns, NVME_TARGET_PASSTHRU);
@@ -3710,7 +3711,7 @@ static void nvme_ns_add_to_ctrl_list(struct nvme_ns *ns)
list_for_each_entry_reverse(tmp, &ns->ctrl->namespaces, list) {
if (tmp->head->ns_id < ns->head->ns_id) {
- list_add(&ns->list, &tmp->list);
+ list_add_rcu(&ns->list, &tmp->list);
return;
}
}
@@ -3776,17 +3777,17 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
if (nvme_update_ns_info(ns, info))
goto out_unlink_ns;
- down_write(&ctrl->namespaces_rwsem);
+ mutex_lock(&ctrl->namespaces_lock);
/*
* 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);
+ mutex_unlock(&ctrl->namespaces_lock);
goto out_unlink_ns;
}
nvme_ns_add_to_ctrl_list(ns);
- up_write(&ctrl->namespaces_rwsem);
+ mutex_unlock(&ctrl->namespaces_lock);
nvme_get_ctrl(ctrl);
if (device_add_disk(ctrl->device, ns->disk, nvme_ns_attr_groups))
@@ -3809,9 +3810,9 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, struct nvme_ns_info *info)
out_cleanup_ns_from_list:
nvme_put_ctrl(ctrl);
- down_write(&ctrl->namespaces_rwsem);
- list_del_init(&ns->list);
- up_write(&ctrl->namespaces_rwsem);
+ mutex_lock(&ctrl->namespaces_lock);
+ list_del_rcu(&ns->list);
+ mutex_unlock(&ctrl->namespaces_lock);
out_unlink_ns:
mutex_lock(&ctrl->subsys->lock);
list_del_rcu(&ns->siblings);
@@ -3861,10 +3862,11 @@ static void nvme_ns_remove(struct nvme_ns *ns)
nvme_cdev_del(&ns->cdev, &ns->cdev_device);
del_gendisk(ns->disk);
- down_write(&ns->ctrl->namespaces_rwsem);
- list_del_init(&ns->list);
- up_write(&ns->ctrl->namespaces_rwsem);
+ mutex_lock(&ns->ctrl->namespaces_lock);
+ list_del_rcu(&ns->list);
+ mutex_unlock(&ns->ctrl->namespaces_lock);
+ synchronize_srcu(&ns->ctrl->srcu);
if (last_path)
nvme_mpath_shutdown_disk(ns->head);
nvme_put_ns(ns);
@@ -3953,16 +3955,17 @@ static void nvme_remove_invalid_namespaces(struct nvme_ctrl *ctrl,
struct nvme_ns *ns, *next;
LIST_HEAD(rm_list);
- down_write(&ctrl->namespaces_rwsem);
+ mutex_lock(&ctrl->namespaces_lock);
list_for_each_entry_safe(ns, next, &ctrl->namespaces, list) {
if (ns->head->ns_id > nsid)
- list_move_tail(&ns->list, &rm_list);
+ list_splice_init_rcu(&ns->list, &rm_list, synchronize_rcu);
}
- up_write(&ctrl->namespaces_rwsem);
+ mutex_unlock(&ctrl->namespaces_lock);
list_for_each_entry_safe(ns, next, &rm_list, list)
nvme_ns_remove(ns);
+ synchronize_srcu(&ctrl->srcu);
}
static int nvme_scan_ns_list(struct nvme_ctrl *ctrl)
@@ -4132,12 +4135,14 @@ void nvme_remove_namespaces(struct nvme_ctrl *ctrl)
/* this is a no-op when called from the controller reset handler */
nvme_change_ctrl_state(ctrl, NVME_CTRL_DELETING_NOIO);
- down_write(&ctrl->namespaces_rwsem);
- list_splice_init(&ctrl->namespaces, &ns_list);
- up_write(&ctrl->namespaces_rwsem);
+ mutex_lock(&ctrl->namespaces_lock);
+ list_splice_init_rcu(&ctrl->namespaces, &ns_list, synchronize_rcu);
+ mutex_unlock(&ctrl->namespaces_lock);
list_for_each_entry_safe(ns, next, &ns_list, list)
nvme_ns_remove(ns);
+
+ synchronize_srcu(&ctrl->srcu);
}
EXPORT_SYMBOL_GPL(nvme_remove_namespaces);
@@ -4582,6 +4587,7 @@ static void nvme_free_ctrl(struct device *dev)
key_put(ctrl->tls_key);
nvme_free_cels(ctrl);
nvme_mpath_uninit(ctrl);
+ cleanup_srcu_struct(&ctrl->srcu);
nvme_auth_stop(ctrl);
nvme_auth_free(ctrl);
__free_page(ctrl->discard_page);
@@ -4614,10 +4620,15 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
ctrl->passthru_err_log_enabled = false;
clear_bit(NVME_CTRL_FAILFAST_EXPIRED, &ctrl->flags);
spin_lock_init(&ctrl->lock);
+ mutex_init(&ctrl->namespaces_lock);
+
+ ret = init_srcu_struct(&ctrl->srcu);
+ if (ret)
+ return ret;
+
mutex_init(&ctrl->scan_lock);
INIT_LIST_HEAD(&ctrl->namespaces);
xa_init(&ctrl->cels);
- init_rwsem(&ctrl->namespaces_rwsem);
ctrl->dev = dev;
ctrl->ops = ops;
ctrl->quirks = quirks;
@@ -4697,6 +4708,7 @@ int nvme_init_ctrl(struct nvme_ctrl *ctrl, struct device *dev,
out:
if (ctrl->discard_page)
__free_page(ctrl->discard_page);
+ cleanup_srcu_struct(&ctrl->srcu);
return ret;
}
EXPORT_SYMBOL_GPL(nvme_init_ctrl);
@@ -4705,22 +4717,24 @@ EXPORT_SYMBOL_GPL(nvme_init_ctrl);
void nvme_mark_namespaces_dead(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list)
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list)
blk_mark_disk_dead(ns->disk);
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
}
EXPORT_SYMBOL_GPL(nvme_mark_namespaces_dead);
void nvme_unfreeze(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list)
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list)
blk_mq_unfreeze_queue(ns->queue);
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
clear_bit(NVME_CTRL_FROZEN, &ctrl->flags);
}
EXPORT_SYMBOL_GPL(nvme_unfreeze);
@@ -4728,14 +4742,15 @@ EXPORT_SYMBOL_GPL(nvme_unfreeze);
int nvme_wait_freeze_timeout(struct nvme_ctrl *ctrl, long timeout)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list) {
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
timeout = blk_mq_freeze_queue_wait_timeout(ns->queue, timeout);
if (timeout <= 0)
break;
}
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
return timeout;
}
EXPORT_SYMBOL_GPL(nvme_wait_freeze_timeout);
@@ -4743,23 +4758,25 @@ EXPORT_SYMBOL_GPL(nvme_wait_freeze_timeout);
void nvme_wait_freeze(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list)
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list)
blk_mq_freeze_queue_wait(ns->queue);
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
}
EXPORT_SYMBOL_GPL(nvme_wait_freeze);
void nvme_start_freeze(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
set_bit(NVME_CTRL_FROZEN, &ctrl->flags);
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list)
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list)
blk_freeze_queue_start(ns->queue);
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
}
EXPORT_SYMBOL_GPL(nvme_start_freeze);
@@ -4802,11 +4819,12 @@ EXPORT_SYMBOL_GPL(nvme_unquiesce_admin_queue);
void nvme_sync_io_queues(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list)
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list)
blk_sync_queue(ns->queue);
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
}
EXPORT_SYMBOL_GPL(nvme_sync_io_queues);
diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index 499a8bb7cac7d..0f05058692b55 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -789,16 +789,16 @@ static int nvme_dev_user_cmd(struct nvme_ctrl *ctrl, void __user *argp,
bool open_for_write)
{
struct nvme_ns *ns;
- int ret;
+ int ret, srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
if (list_empty(&ctrl->namespaces)) {
ret = -ENOTTY;
goto out_unlock;
}
- ns = list_first_entry(&ctrl->namespaces, struct nvme_ns, list);
- if (ns != list_last_entry(&ctrl->namespaces, struct nvme_ns, list)) {
+ ns = list_first_or_null_rcu(&ctrl->namespaces, struct nvme_ns, list);
+ if (!ns) {
dev_warn(ctrl->device,
"NVME_IOCTL_IO_CMD not supported when multiple namespaces present!\n");
ret = -EINVAL;
@@ -808,14 +808,14 @@ static int nvme_dev_user_cmd(struct nvme_ctrl *ctrl, void __user *argp,
dev_warn(ctrl->device,
"using deprecated NVME_IOCTL_IO_CMD ioctl on the char device!\n");
kref_get(&ns->kref);
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
ret = nvme_user_cmd(ctrl, ns, argp, 0, open_for_write);
nvme_put_ns(ns);
return ret;
out_unlock:
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
return ret;
}
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 1bee176fd850e..d8b6b4648eaff 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -151,16 +151,17 @@ void nvme_mpath_end_request(struct request *rq)
void nvme_kick_requeue_lists(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list) {
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
if (!ns->head->disk)
continue;
kblockd_schedule_work(&ns->head->requeue_work);
if (nvme_ctrl_state(ns->ctrl) == NVME_CTRL_LIVE)
disk_uevent(ns->head->disk, KOBJ_CHANGE);
}
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
}
static const char *nvme_ana_state_names[] = {
@@ -194,13 +195,14 @@ bool nvme_mpath_clear_current_path(struct nvme_ns *ns)
void nvme_mpath_clear_ctrl_paths(struct nvme_ctrl *ctrl)
{
struct nvme_ns *ns;
+ int srcu_idx;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list) {
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
nvme_mpath_clear_current_path(ns);
kblockd_schedule_work(&ns->head->requeue_work);
}
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
}
void nvme_mpath_revalidate_paths(struct nvme_ns *ns)
@@ -681,6 +683,7 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
u32 nr_nsids = le32_to_cpu(desc->nnsids), n = 0;
unsigned *nr_change_groups = data;
struct nvme_ns *ns;
+ int srcu_idx;
dev_dbg(ctrl->device, "ANA group %d: %s.\n",
le32_to_cpu(desc->grpid),
@@ -692,8 +695,8 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
if (!nr_nsids)
return 0;
- down_read(&ctrl->namespaces_rwsem);
- list_for_each_entry(ns, &ctrl->namespaces, list) {
+ srcu_idx = srcu_read_lock(&ctrl->srcu);
+ list_for_each_entry_rcu(ns, &ctrl->namespaces, list) {
unsigned nsid;
again:
nsid = le32_to_cpu(desc->nsids[n]);
@@ -706,7 +709,7 @@ static int nvme_update_ana_state(struct nvme_ctrl *ctrl,
if (ns->head->ns_id > nsid)
goto again;
}
- up_read(&ctrl->namespaces_rwsem);
+ srcu_read_unlock(&ctrl->srcu, srcu_idx);
return 0;
}
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index fc31bd340a63a..a005941a8b67e 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -282,7 +282,8 @@ struct nvme_ctrl {
struct blk_mq_tag_set *tagset;
struct blk_mq_tag_set *admin_tagset;
struct list_head namespaces;
- struct rw_semaphore namespaces_rwsem;
+ struct mutex namespaces_lock;
+ struct srcu_struct srcu;
struct device ctrl_device;
struct device *device; /* char device */
#ifdef CONFIG_NVME_HWMON
--
2.43.0
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