sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 354 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-net b/Documentation/ABI/testing/sysfs-class-net
new file mode 100644
index 000000000..ebf21beba
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-net
@@ -0,0 +1,354 @@
+What:		/sys/class/net/<iface>/name_assign_type
+Date:		July 2014
+KernelVersion:	3.17
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the name assignment type. Possible values are:
+
+		== ==========================================================
+		1  enumerated by the kernel, possibly in an unpredictable way
+		2  predictably named by the kernel
+		3  named by userspace
+		4  renamed
+		== ==========================================================
+
+What:		/sys/class/net/<iface>/addr_assign_type
+Date:		July 2010
+KernelVersion:	3.2
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the address assignment type. Possible values are:
+
+		== =============================
+		0  permanent address
+		1  randomly generated
+		2  stolen from another device
+		3  set using dev_set_mac_address
+		== =============================
+
+What:		/sys/class/net/<iface>/addr_len
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the hardware address size in bytes.
+		Values vary based on the lower-level protocol used by the
+		interface (Ethernet, FDDI, ATM, IEEE 802.15.4...). See
+		include/uapi/linux/if_*.h for actual values.
+
+What:		/sys/class/net/<iface>/address
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Hardware address currently assigned to this interface.
+		Format is a string, e.g: 00:11:22:33:44:55 for an Ethernet MAC
+		address.
+
+What:		/sys/class/net/<bridge iface>/bridge/group_fwd_mask
+Date:		January 2012
+KernelVersion:	3.2
+Contact:	netdev@vger.kernel.org
+Description:
+		Bitmask to allow forwarding of link local frames with address
+		01-80-C2-00-00-0X on a bridge device. Only values that set bits
+		not matching BR_GROUPFWD_RESTRICTED in net/bridge/br_private.h
+		allowed.
+		Default value 0 does not forward any link local frames.
+
+		Restricted bits:
+
+		== ========================================================
+		0  01-80-C2-00-00-00 Bridge Group Address used for STP
+		1  01-80-C2-00-00-01 (MAC Control) 802.3 used for MAC PAUSE
+		2  01-80-C2-00-00-02 (Link Aggregation) 802.3ad
+		== ========================================================
+
+		Any values not setting these bits can be used. Take special
+		care when forwarding control frames e.g. 802.1X-PAE or LLDP.
+
+What:		/sys/class/net/<iface>/broadcast
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Hardware broadcast address for this interface. Format is a
+		string, e.g: ff:ff:ff:ff:ff:ff for an Ethernet broadcast MAC
+		address.
+
+What:		/sys/class/net/<iface>/carrier
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the current physical link state of the interface.
+		Possible values are:
+
+		== =====================
+		0  physical link is down
+		1  physical link is up
+		== =====================
+
+		Note: some special devices, e.g: bonding and team drivers will
+		allow this attribute to be written to force a link state for
+		operating correctly and designating another fallback interface.
+
+What:		/sys/class/net/<iface>/dev_id
+Date:		April 2008
+KernelVersion:	2.6.26
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the device unique identifier. Format is an hexadecimal
+		value. This is used to disambiguate interfaces which might be
+		stacked (e.g: VLAN interfaces) but still have the same MAC
+		address as their parent device.
+
+What:		/sys/class/net/<iface>/dev_port
+Date:		February 2014
+KernelVersion:	3.15
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the port number of this network device, formatted
+		as a decimal value. Some NICs have multiple independent ports
+		on the same PCI bus, device and function. This attribute allows
+		userspace to distinguish the respective interfaces.
+
+		Note: some device drivers started to use 'dev_id' for this
+		purpose since long before 3.15 and have not adopted the new
+		attribute ever since. To query the port number, some tools look
+		exclusively at 'dev_port', while others only consult 'dev_id'.
+		If a network device has multiple client adapter ports as
+		described in the previous paragraph and does not set this
+		attribute to its port number, it's a kernel bug.
+
+What:		/sys/class/net/<iface>/dormant
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates whether the interface is in dormant state. Possible
+		values are:
+		0: interface is not dormant
+		1: interface is dormant
+
+		This attribute can be used by supplicant software to signal that
+		the device is not usable unless some supplicant-based
+		authentication is performed (e.g: 802.1x). 'link_mode' attribute
+		will also reflect the dormant state.
+
+What:		/sys/class/net/<iface>/testing
+Date:		April 2002
+KernelVersion:	5.8
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates whether the interface is under test. Possible
+		values are:
+
+		== =============================
+		0  interface is not being tested
+		1  interface is being tested
+		== =============================
+
+		When an interface is under test, it cannot be expected
+		to pass packets as normal.
+
+What:		/sys/class/net/<iface>/duplex
+Date:		October 2009
+KernelVersion:	2.6.33
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface latest or current duplex value. Possible
+		values are:
+
+		====  ===========
+		half  half duplex
+		full  full duplex
+		====  ===========
+
+		Note: This attribute is only valid for interfaces that implement
+		the ethtool get_link_ksettings method (mostly Ethernet).
+
+What:		/sys/class/net/<iface>/flags
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface flags as a bitmask in hexadecimal. See
+		include/uapi/linux/if.h for a list of all possible values and
+		the flags semantics.
+
+What:		/sys/class/net/<iface>/ifalias
+Date:		September 2008
+KernelVersion:	2.6.28
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates/stores an interface alias name as a string. This can
+		be used for system management purposes.
+
+What:		/sys/class/net/<iface>/ifindex
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the system-wide interface unique index identifier as a
+		decimal number. This attribute is used for mapping an interface
+		identifier to an interface name. It is used throughout the
+		networking stack for specifying the interface specific
+		requests/events.
+
+What:		/sys/class/net/<iface>/iflink
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the system-wide interface unique index identifier a
+		the interface is linked to. Format is decimal. This attribute is
+		used to resolve interfaces chaining, linking and stacking.
+		Physical interfaces have the same 'ifindex' and 'iflink' values.
+
+What:		/sys/class/net/<iface>/link_mode
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface link mode, as a decimal number. This
+		attribute should be used in conjunction with 'dormant' attribute
+		to determine the interface usability. Possible values:
+
+		==  =================
+		0   default link mode
+		1   dormant link mode
+		==  =================
+
+What:		/sys/class/net/<iface>/mtu
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface currently configured MTU value, in
+		bytes, and in decimal format. Specific values depends on the
+		lower-level interface protocol used. Ethernet devices will show
+		a 'mtu' attribute value of 1500 unless changed.
+
+What:		/sys/class/net/<iface>/netdev_group
+Date:		January 2011
+KernelVersion:	2.6.39
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface network device group, as a decimal
+		integer. Default value is 0 which corresponds to the initial
+		network devices group. The group can be changed to affect
+		routing decisions (see: net/ipv4/fib_rules and
+		net/ipv6/fib6_rules.c).
+
+What:		/sys/class/net/<iface>/operstate
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface RFC2863 operational state as a string.
+
+		Possible values are:
+
+		"unknown", "notpresent", "down", "lowerlayerdown", "testing",
+		"dormant", "up".
+
+What:		/sys/class/net/<iface>/phys_port_id
+Date:		July 2013
+KernelVersion:	3.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface unique physical port identifier within
+		the NIC, as a string.
+
+What:		/sys/class/net/<iface>/phys_port_name
+Date:		March 2015
+KernelVersion:	4.0
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface physical port name within the NIC,
+		as a string.
+
+What:		/sys/class/net/<iface>/speed
+Date:		October 2009
+KernelVersion:	2.6.33
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface latest or current speed value. Value is
+		an integer representing the link speed in Mbits/sec.
+
+		Note: this attribute is only valid for interfaces that implement
+		the ethtool get_link_ksettings method (mostly Ethernet).
+
+What:		/sys/class/net/<iface>/tx_queue_len
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface transmit queue len in number of packets,
+		as an integer value. Value depend on the type of interface,
+		Ethernet network adapters have a default value of 1000 unless
+		configured otherwise
+
+What:		/sys/class/net/<iface>/type
+Date:		April 2005
+KernelVersion:	2.6.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the interface protocol type as a decimal value. See
+		include/uapi/linux/if_arp.h for all possible values.
+
+What:		/sys/class/net/<iface>/phys_switch_id
+Date:		November 2014
+KernelVersion:	3.19
+Contact:	netdev@vger.kernel.org
+Description:
+		Indicates the unique physical switch identifier of a switch this
+		port belongs to, as a string.
+
+What:		/sys/class/net/<iface>/phydev
+Date:		May 2017
+KernelVersion:	4.13
+Contact:	netdev@vger.kernel.org
+Description:
+		Symbolic link to the PHY device this network device is attached
+		to.
+
+What:		/sys/class/net/<iface>/carrier_changes
+Date:		Mar 2014
+KernelVersion:	3.15
+Contact:	netdev@vger.kernel.org
+Description:
+		32-bit unsigned integer counting the number of times the link has
+		seen a change from UP to DOWN and vice versa
+
+What:		/sys/class/net/<iface>/carrier_up_count
+Date:		Jan 2018
+KernelVersion:	4.16
+Contact:	netdev@vger.kernel.org
+Description:
+		32-bit unsigned integer counting the number of times the link has
+		been up
+
+What:		/sys/class/net/<iface>/carrier_down_count
+Date:		Jan 2018
+KernelVersion:	4.16
+Contact:	netdev@vger.kernel.org
+Description:
+		32-bit unsigned integer counting the number of times the link has
+		been down
+
+What:		/sys/class/net/<iface>/threaded
+Date:		Jan 2021
+KernelVersion:	5.12
+Contact:	netdev@vger.kernel.org
+Description:
+		Boolean value to control the threaded mode per device. User could
+		set this value to enable/disable threaded mode for all napi
+		belonging to this device, without the need to do device up/down.
+
+		Possible values:
+		== ==================================
+		0  threaded mode disabled for this dev
+		1  threaded mode enabled for this dev
+		== ==================================