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Date: Mon, 27 Jan 2020 20:04:14 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Taehee Yoo <ap420073@...il.com>
Cc: davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 2/6] netdevsim: disable devlink reload when
resources are being used
On Mon, 27 Jan 2020 14:30:15 +0000, Taehee Yoo wrote:
> devlink reload destroys resources and allocates resources again.
> So, when devices and ports resources are being used, devlink reload
> function should not be executed. In order to avoid this race, a new
> lock is added and new_port() and del_port() call devlink_reload_disable()
> and devlink_reload_enable().
>
> Thread0 Thread1
> {new/del}_port() {new/del}_port()
> devlink_reload_disable()
> devlink_reload_disable()
> devlink_reload_enable() //here
> devlink_reload_enable()
>
> Before Thread1's devlink_reload_enable(), the devlink is already allowed
> to execute reload because Thread0 allows it. devlink reload disable/enable
> variable type is bool. So the above case would exist.
> So, disable/enable should be executed atomically.
> In order to do that, a new lock is used.
>
> Test commands:
> modprobe netdevsim
> echo 1 > /sys/bus/netdevsim/new_device
>
> while :
> do
> echo 1 > /sys/devices/netdevsim1/new_port &
> echo 1 > /sys/devices/netdevsim1/del_port &
> devlink dev reload netdevsim/netdevsim1 &
> done
>
> Splat looks like:
> [ 1067.313531][ T1480] kernel BUG at lib/list_debug.c:53!
> [ 1067.314519][ T1480] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
> [ 1067.315948][ T1480] CPU: 3 PID: 1480 Comm: bash Tainted: G W 5.5.0-rc6+ #318
> [ 1067.326082][ T1480] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
> [ 1067.356308][ T1480] RIP: 0010:__list_del_entry_valid+0xe6/0x150
> [ 1067.357006][ T1480] Code: 89 ea 48 c7 c7 a0 64 1e 9f e8 7f 5b 4d ff 0f 0b 48 c7 c7 00 65 1e 9f e8 71 5b 4d ff 4
> [ 1067.395359][ T1480] RSP: 0018:ffff8880a316fb58 EFLAGS: 00010282
> [ 1067.396016][ T1480] RAX: 0000000000000054 RBX: ffff8880c0e76718 RCX: 0000000000000000
> [ 1067.402370][ T1480] RDX: 0000000000000054 RSI: 0000000000000008 RDI: ffffed101462df61
> [ 1067.430844][ T1480] RBP: ffff8880a31bfca0 R08: ffffed101b5404f9 R09: ffffed101b5404f9
> [ 1067.432165][ T1480] R10: 0000000000000001 R11: ffffed101b5404f8 R12: ffff8880a316fcb0
> [ 1067.433526][ T1480] R13: ffff8880a310d440 R14: ffffffffa117a7c0 R15: ffff8880c0e766c0
> [ 1067.435818][ T1480] FS: 00007f001c026740(0000) GS:ffff8880da800000(0000) knlGS:0000000000000000
> [ 1067.441677][ T1480] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 1067.451305][ T1480] CR2: 00007f001afb7180 CR3: 00000000a3170003 CR4: 00000000000606e0
> [ 1067.453416][ T1480] Call Trace:
> [ 1067.453832][ T1480] mutex_remove_waiter+0x101/0x520
> [ 1067.455949][ T1480] __mutex_lock+0xac7/0x14b0
> [ 1067.456880][ T1480] ? nsim_dev_port_add+0x50/0x150 [netdevsim]
> [ 1067.458946][ T1480] ? mutex_lock_io_nested+0x1380/0x1380
> [ 1067.460614][ T1480] ? _parse_integer+0xf0/0xf0
> [ 1067.472498][ T1480] ? kstrtouint+0x86/0x110
> [ 1067.473327][ T1480] ? nsim_dev_port_add+0x50/0x150 [netdevsim]
> [ 1067.474187][ T1480] nsim_dev_port_add+0x50/0x150 [netdevsim]
> [ 1067.474980][ T1480] new_port_store+0xc4/0xf0 [netdevsim]
> [ 1067.475717][ T1480] ? del_port_store+0xf0/0xf0 [netdevsim]
> [ 1067.476478][ T1480] ? sysfs_kf_write+0x3b/0x180
> [ 1067.477106][ T1480] ? sysfs_file_ops+0x160/0x160
> [ 1067.477744][ T1480] kernfs_fop_write+0x276/0x410
> [ ... ]
>
> Fixes: 4418f862d675 ("netdevsim: implement support for devlink region and snapshots")
> Fixes: 75ba029f3c07 ("netdevsim: implement proper devlink reload")
> Signed-off-by: Taehee Yoo <ap420073@...il.com>
> ---
> drivers/net/netdevsim/bus.c | 21 ++++++++++++++++++++-
> drivers/net/netdevsim/dev.c | 14 ++++++++++++++
> drivers/net/netdevsim/netdevsim.h | 4 ++++
> 3 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/netdevsim/bus.c b/drivers/net/netdevsim/bus.c
> index a3205fd73c8f..b1aed37a0574 100644
> --- a/drivers/net/netdevsim/bus.c
> +++ b/drivers/net/netdevsim/bus.c
> @@ -16,7 +16,7 @@
>
> static DEFINE_IDA(nsim_bus_dev_ids);
> static LIST_HEAD(nsim_bus_dev_list);
> -static DEFINE_MUTEX(nsim_bus_dev_ops_lock);
> +DEFINE_MUTEX(nsim_bus_dev_ops_lock);
> static bool enable;
>
> static struct nsim_bus_dev *to_nsim_bus_dev(struct device *dev)
> @@ -97,6 +97,8 @@ new_port_store(struct device *dev, struct device_attribute *attr,
> const char *buf, size_t count)
> {
> struct nsim_bus_dev *nsim_bus_dev = to_nsim_bus_dev(dev);
> + struct nsim_dev *nsim_dev = dev_get_drvdata(dev);
> + struct devlink *devlink;
> unsigned int port_index;
> int ret;
>
> @@ -105,7 +107,14 @@ new_port_store(struct device *dev, struct device_attribute *attr,
> ret = kstrtouint(buf, 0, &port_index);
> if (ret)
> return ret;
> +
> + devlink = priv_to_devlink(nsim_dev);
> +
> + mutex_lock(&nsim_bus_dev->port_ops_lock);
> + devlink_reload_disable(devlink);
> ret = nsim_dev_port_add(nsim_bus_dev, port_index);
> + devlink_reload_enable(devlink);
> + mutex_unlock(&nsim_bus_dev->port_ops_lock);
> return ret ? ret : count;
> }
>
> @@ -116,6 +125,8 @@ del_port_store(struct device *dev, struct device_attribute *attr,
> const char *buf, size_t count)
> {
> struct nsim_bus_dev *nsim_bus_dev = to_nsim_bus_dev(dev);
> + struct nsim_dev *nsim_dev = dev_get_drvdata(dev);
> + struct devlink *devlink;
> unsigned int port_index;
> int ret;
>
> @@ -124,7 +135,14 @@ del_port_store(struct device *dev, struct device_attribute *attr,
> ret = kstrtouint(buf, 0, &port_index);
> if (ret)
> return ret;
> +
> + devlink = priv_to_devlink(nsim_dev);
> +
> + mutex_lock(&nsim_bus_dev->port_ops_lock);
> + devlink_reload_disable(devlink);
> ret = nsim_dev_port_del(nsim_bus_dev, port_index);
> + devlink_reload_enable(devlink);
> + mutex_unlock(&nsim_bus_dev->port_ops_lock);
> return ret ? ret : count;
> }
>
> @@ -301,6 +319,7 @@ nsim_bus_dev_new(unsigned int id, unsigned int port_count)
> nsim_bus_dev->dev.type = &nsim_bus_dev_type;
> nsim_bus_dev->port_count = port_count;
> nsim_bus_dev->initial_net = current->nsproxy->net_ns;
> + mutex_init(&nsim_bus_dev->port_ops_lock);
>
> err = device_register(&nsim_bus_dev->dev);
> if (err)
Disabling reload around port add/del makes perfect sense
> diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
> index 4b39aba2e9c4..0dfaf999e8db 100644
> --- a/drivers/net/netdevsim/dev.c
> +++ b/drivers/net/netdevsim/dev.c
> @@ -43,6 +43,8 @@ static ssize_t nsim_dev_take_snapshot_write(struct file *file,
> size_t count, loff_t *ppos)
> {
> struct nsim_dev *nsim_dev = file->private_data;
> + struct nsim_bus_dev *nsim_bus_dev;
> + struct devlink *devlink;
> void *dummy_data;
> int err;
> u32 id;
> @@ -51,11 +53,23 @@ static ssize_t nsim_dev_take_snapshot_write(struct file *file,
> if (!dummy_data)
> return -ENOMEM;
>
> + devlink = priv_to_devlink(nsim_dev);
> + nsim_bus_dev = nsim_dev->nsim_bus_dev;
> +
> get_random_bytes(dummy_data, NSIM_DEV_DUMMY_REGION_SIZE);
>
> + mutex_lock(&nsim_bus_dev_ops_lock);
Not sure why we have to lock the big lock here?
> + mutex_lock(&nsim_bus_dev->port_ops_lock);
> + devlink_reload_disable(devlink);
Or the port lock, or disable reload - the reload path unregisters and
re-registers the snapshot, so snapshot can't be taken during reload,
I don't think.
> id = devlink_region_snapshot_id_get(priv_to_devlink(nsim_dev));
> err = devlink_region_snapshot_create(nsim_dev->dummy_region,
> dummy_data, id, kfree);
> +
> + devlink_reload_enable(devlink);
> + mutex_unlock(&nsim_bus_dev->port_ops_lock);
> + mutex_unlock(&nsim_bus_dev_ops_lock);
> +
> if (err) {
> pr_err("Failed to create region snapshot\n");
> kfree(dummy_data);
> diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
> index ea3931391ce2..a8b6c9e6f79f 100644
> --- a/drivers/net/netdevsim/netdevsim.h
> +++ b/drivers/net/netdevsim/netdevsim.h
> @@ -74,6 +74,8 @@ struct netdevsim {
> struct nsim_ipsec ipsec;
> };
>
> +extern struct mutex nsim_bus_dev_ops_lock;
> +
> struct netdevsim *
> nsim_create(struct nsim_dev *nsim_dev, struct nsim_dev_port *nsim_dev_port);
> void nsim_destroy(struct netdevsim *ns);
> @@ -240,6 +242,8 @@ struct nsim_bus_dev {
> */
> unsigned int num_vfs;
> struct nsim_vf_config *vfconfigs;
> + /* Lock for new_port() and del_port() to disable devlink reload */
It'd be good to have the comment point out which fields the lock
protects, rather than code.
> + struct mutex port_ops_lock;
> bool init;
> };
>
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