From 5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 21 Feb 2023 18:24:12 -0800 Subject: Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next Pull networking updates from Jakub Kicinski: "Core: - Add dedicated kmem_cache for typical/small skb->head, avoid having to access struct page at kfree time, and improve memory use. - Introduce sysctl to set default RPS configuration for new netdevs. - Define Netlink protocol specification format which can be used to describe messages used by each family and auto-generate parsers. Add tools for generating kernel data structures and uAPI headers. - Expose all net/core sysctls inside netns. - Remove 4s sleep in netpoll if carrier is instantly detected on boot. - Add configurable limit of MDB entries per port, and port-vlan. - Continue populating drop reasons throughout the stack. - Retire a handful of legacy Qdiscs and classifiers. Protocols: - Support IPv4 big TCP (TSO frames larger than 64kB). - Add IP_LOCAL_PORT_RANGE socket option, to control local port range on socket by socket basis. - Track and report in procfs number of MPTCP sockets used. - Support mixing IPv4 and IPv6 flows in the in-kernel MPTCP path manager. - IPv6: don't check net.ipv6.route.max_size and rely on garbage collection to free memory (similarly to IPv4). - Support Penultimate Segment Pop (PSP) flavor in SRv6 (RFC8986). - ICMP: add per-rate limit counters. - Add support for user scanning requests in ieee802154. - Remove static WEP support. - Support minimal Wi-Fi 7 Extremely High Throughput (EHT) rate reporting. - WiFi 7 EHT channel puncturing support (client & AP). BPF: - Add a rbtree data structure following the "next-gen data structure" precedent set by recently added linked list, that is, by using kfunc + kptr instead of adding a new BPF map type. - Expose XDP hints via kfuncs with initial support for RX hash and timestamp metadata. - Add BPF_F_NO_TUNNEL_KEY extension to bpf_skb_set_tunnel_key to better support decap on GRE tunnel devices not operating in collect metadata. - Improve x86 JIT's codegen for PROBE_MEM runtime error checks. - Remove the need for trace_printk_lock for bpf_trace_printk and bpf_trace_vprintk helpers. - Extend libbpf's bpf_tracing.h support for tracing arguments of kprobes/uprobes and syscall as a special case. - Significantly reduce the search time for module symbols by livepatch and BPF. - Enable cpumasks to be used as kptrs, which is useful for tracing programs tracking which tasks end up running on which CPUs in different time intervals. - Add support for BPF trampoline on s390x and riscv64. - Add capability to export the XDP features supported by the NIC. - Add __bpf_kfunc tag for marking kernel functions as kfuncs. - Add cgroup.memory=nobpf kernel parameter option to disable BPF memory accounting for container environments. Netfilter: - Remove the CLUSTERIP target. It has been marked as obsolete for years, and we still have WARN splats wrt races of the out-of-band /proc interface installed by this target. - Add 'destroy' commands to nf_tables. They are identical to the existing 'delete' commands, but do not return an error if the referenced object (set, chain, rule...) did not exist. Driver API: - Improve cpumask_local_spread() locality to help NICs set the right IRQ affinity on AMD platforms. - Separate C22 and C45 MDIO bus transactions more clearly. - Introduce new DCB table to control DSCP rewrite on egress. - Support configuration of Physical Layer Collision Avoidance (PLCA) Reconciliation Sublayer (RS) (802.3cg-2019). Modern version of shared medium Ethernet. - Support for MAC Merge layer (IEEE 802.3-2018 clause 99). Allowing preemption of low priority frames by high priority frames. - Add support for controlling MACSec offload using netlink SET. - Rework devlink instance refcounts to allow registration and de-registration under the instance lock. Split the code into multiple files, drop some of the unnecessarily granular locks and factor out common parts of netlink operation handling. - Add TX frame aggregation parameters (for USB drivers). - Add a new attr TCA_EXT_WARN_MSG to report TC (offload) warning messages with notifications for debug. - Allow offloading of UDP NEW connections via act_ct. - Add support for per action HW stats in TC. - Support hardware miss to TC action (continue processing in SW from a specific point in the action chain). - Warn if old Wireless Extension user space interface is used with modern cfg80211/mac80211 drivers. Do not support Wireless Extensions for Wi-Fi 7 devices at all. Everyone should switch to using nl80211 interface instead. - Improve the CAN bit timing configuration. Use extack to return error messages directly to user space, update the SJW handling, including the definition of a new default value that will benefit CAN-FD controllers, by increasing their oscillator tolerance. New hardware / drivers: - Ethernet: - nVidia BlueField-3 support (control traffic driver) - Ethernet support for imx93 SoCs - Motorcomm yt8531 gigabit Ethernet PHY - onsemi NCN26000 10BASE-T1S PHY (with support for PLCA) - Microchip LAN8841 PHY (incl. cable diagnostics and PTP) - Amlogic gxl MDIO mux - WiFi: - RealTek RTL8188EU (rtl8xxxu) - Qualcomm Wi-Fi 7 devices (ath12k) - CAN: - Renesas R-Car V4H Drivers: - Bluetooth: - Set Per Platform Antenna Gain (PPAG) for Intel controllers. - Ethernet NICs: - Intel (1G, igc): - support TSN / Qbv / packet scheduling features of i226 model - Intel (100G, ice): - use GNSS subsystem instead of TTY - multi-buffer XDP support - extend support for GPIO pins to E823 devices - nVidia/Mellanox: - update the shared buffer configuration on PFC commands - implement PTP adjphase function for HW offset control - TC support for Geneve and GRE with VF tunnel offload - more efficient crypto key management method - multi-port eswitch support - Netronome/Corigine: - add DCB IEEE support - support IPsec offloading for NFP3800 - Freescale/NXP (enetc): - support XDP_REDIRECT for XDP non-linear buffers - improve reconfig, avoid link flap and waiting for idle - support MAC Merge layer - Other NICs: - sfc/ef100: add basic devlink support for ef100 - ionic: rx_push mode operation (writing descriptors via MMIO) - bnxt: use the auxiliary bus abstraction for RDMA - r8169: disable ASPM and reset bus in case of tx timeout - cpsw: support QSGMII mode for J721e CPSW9G - cpts: support pulse-per-second output - ngbe: add an mdio bus driver - usbnet: optimize usbnet_bh() by avoiding unnecessary queuing - r8152: handle devices with FW with NCM support - amd-xgbe: support 10Mbps, 2.5GbE speeds and rx-adaptation - virtio-net: support multi buffer XDP - virtio/vsock: replace virtio_vsock_pkt with sk_buff - tsnep: XDP support - Ethernet high-speed switches: - nVidia/Mellanox (mlxsw): - add support for latency TLV (in FW control messages) - Microchip (sparx5): - separate explicit and implicit traffic forwarding rules, make the implicit rules always active - add support for egress DSCP rewrite - IS0 VCAP support (Ingress Classification) - IS2 VCAP filters (protos, L3 addrs, L4 ports, flags, ToS etc.) - ES2 VCAP support (Egress Access Control) - support for Per-Stream Filtering and Policing (802.1Q, 8.6.5.1) - Ethernet embedded switches: - Marvell (mv88e6xxx): - add MAB (port auth) offload support - enable PTP receive for mv88e6390 - NXP (ocelot): - support MAC Merge layer - support for the the vsc7512 internal copper phys - Microchip: - lan9303: convert to PHYLINK - lan966x: support TC flower filter statistics - lan937x: PTP support for KSZ9563/KSZ8563 and LAN937x - lan937x: support Credit Based Shaper configuration - ksz9477: support Energy Efficient Ethernet - other: - qca8k: convert to regmap read/write API, use bulk operations - rswitch: Improve TX timestamp accuracy - Intel WiFi (iwlwifi): - EHT (Wi-Fi 7) rate reporting - STEP equalizer support: transfer some STEP (connection to radio on platforms with integrated wifi) related parameters from the BIOS to the firmware. - Qualcomm 802.11ax WiFi (ath11k): - IPQ5018 support - Fine Timing Measurement (FTM) responder role support - channel 177 support - MediaTek WiFi (mt76): - per-PHY LED support - mt7996: EHT (Wi-Fi 7) support - Wireless Ethernet Dispatch (WED) reset support - switch to using page pool allocator - RealTek WiFi (rtw89): - support new version of Bluetooth co-existance - Mobile: - rmnet: support TX aggregation" * tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next: (1872 commits) page_pool: add a comment explaining the fragment counter usage net: ethtool: fix __ethtool_dev_mm_supported() implementation ethtool: pse-pd: Fix double word in comments xsk: add linux/vmalloc.h to xsk.c sefltests: netdevsim: wait for devlink instance after netns removal selftest: fib_tests: Always cleanup before exit net/mlx5e: Align IPsec ASO result memory to be as required by hardware net/mlx5e: TC, Set CT miss to the specific ct action instance net/mlx5e: Rename CHAIN_TO_REG to MAPPED_OBJ_TO_REG net/mlx5: Refactor tc miss handling to a single function net/mlx5: Kconfig: Make tc offload depend on tc skb extension net/sched: flower: Support hardware miss to tc action net/sched: flower: Move filter handle initialization earlier net/sched: cls_api: Support hardware miss to tc action net/sched: Rename user cookie and act cookie sfc: fix builds without CONFIG_RTC_LIB sfc: clean up some inconsistent indentings net/mlx4_en: Introduce flexible array to silence overflow warning net: lan966x: Fix possible deadlock inside PTP net/ulp: Remove redundant ->clone() test in inet_clone_ulp(). ... --- Documentation/locking/spinlocks.rst | 165 ++++++++++++++++++++++++++++++++++++ 1 file changed, 165 insertions(+) create mode 100644 Documentation/locking/spinlocks.rst (limited to 'Documentation/locking/spinlocks.rst') diff --git a/Documentation/locking/spinlocks.rst b/Documentation/locking/spinlocks.rst new file mode 100644 index 000000000..bec96f7a9 --- /dev/null +++ b/Documentation/locking/spinlocks.rst @@ -0,0 +1,165 @@ +=============== +Locking lessons +=============== + +Lesson 1: Spin locks +==================== + +The most basic primitive for locking is spinlock:: + + static DEFINE_SPINLOCK(xxx_lock); + + unsigned long flags; + + spin_lock_irqsave(&xxx_lock, flags); + ... critical section here .. + spin_unlock_irqrestore(&xxx_lock, flags); + +The above is always safe. It will disable interrupts _locally_, but the +spinlock itself will guarantee the global lock, so it will guarantee that +there is only one thread-of-control within the region(s) protected by that +lock. This works well even under UP also, so the code does _not_ need to +worry about UP vs SMP issues: the spinlocks work correctly under both. + + NOTE! Implications of spin_locks for memory are further described in: + + Documentation/memory-barriers.txt + + (5) ACQUIRE operations. + + (6) RELEASE operations. + +The above is usually pretty simple (you usually need and want only one +spinlock for most things - using more than one spinlock can make things a +lot more complex and even slower and is usually worth it only for +sequences that you **know** need to be split up: avoid it at all cost if you +aren't sure). + +This is really the only really hard part about spinlocks: once you start +using spinlocks they tend to expand to areas you might not have noticed +before, because you have to make sure the spinlocks correctly protect the +shared data structures **everywhere** they are used. The spinlocks are most +easily added to places that are completely independent of other code (for +example, internal driver data structures that nobody else ever touches). + + NOTE! The spin-lock is safe only when you **also** use the lock itself + to do locking across CPU's, which implies that EVERYTHING that + touches a shared variable has to agree about the spinlock they want + to use. + +---- + +Lesson 2: reader-writer spinlocks. +================================== + +If your data accesses have a very natural pattern where you usually tend +to mostly read from the shared variables, the reader-writer locks +(rw_lock) versions of the spinlocks are sometimes useful. They allow multiple +readers to be in the same critical region at once, but if somebody wants +to change the variables it has to get an exclusive write lock. + + NOTE! reader-writer locks require more atomic memory operations than + simple spinlocks. Unless the reader critical section is long, you + are better off just using spinlocks. + +The routines look the same as above:: + + rwlock_t xxx_lock = __RW_LOCK_UNLOCKED(xxx_lock); + + unsigned long flags; + + read_lock_irqsave(&xxx_lock, flags); + .. critical section that only reads the info ... + read_unlock_irqrestore(&xxx_lock, flags); + + write_lock_irqsave(&xxx_lock, flags); + .. read and write exclusive access to the info ... + write_unlock_irqrestore(&xxx_lock, flags); + +The above kind of lock may be useful for complex data structures like +linked lists, especially searching for entries without changing the list +itself. The read lock allows many concurrent readers. Anything that +**changes** the list will have to get the write lock. + + NOTE! RCU is better for list traversal, but requires careful + attention to design detail (see Documentation/RCU/listRCU.rst). + +Also, you cannot "upgrade" a read-lock to a write-lock, so if you at _any_ +time need to do any changes (even if you don't do it every time), you have +to get the write-lock at the very beginning. + + NOTE! We are working hard to remove reader-writer spinlocks in most + cases, so please don't add a new one without consensus. (Instead, see + Documentation/RCU/rcu.rst for complete information.) + +---- + +Lesson 3: spinlocks revisited. +============================== + +The single spin-lock primitives above are by no means the only ones. They +are the most safe ones, and the ones that work under all circumstances, +but partly **because** they are safe they are also fairly slow. They are slower +than they'd need to be, because they do have to disable interrupts +(which is just a single instruction on a x86, but it's an expensive one - +and on other architectures it can be worse). + +If you have a case where you have to protect a data structure across +several CPU's and you want to use spinlocks you can potentially use +cheaper versions of the spinlocks. IFF you know that the spinlocks are +never used in interrupt handlers, you can use the non-irq versions:: + + spin_lock(&lock); + ... + spin_unlock(&lock); + +(and the equivalent read-write versions too, of course). The spinlock will +guarantee the same kind of exclusive access, and it will be much faster. +This is useful if you know that the data in question is only ever +manipulated from a "process context", ie no interrupts involved. + +The reasons you mustn't use these versions if you have interrupts that +play with the spinlock is that you can get deadlocks:: + + spin_lock(&lock); + ... + <- interrupt comes in: + spin_lock(&lock); + +where an interrupt tries to lock an already locked variable. This is ok if +the other interrupt happens on another CPU, but it is _not_ ok if the +interrupt happens on the same CPU that already holds the lock, because the +lock will obviously never be released (because the interrupt is waiting +for the lock, and the lock-holder is interrupted by the interrupt and will +not continue until the interrupt has been processed). + +(This is also the reason why the irq-versions of the spinlocks only need +to disable the _local_ interrupts - it's ok to use spinlocks in interrupts +on other CPU's, because an interrupt on another CPU doesn't interrupt the +CPU that holds the lock, so the lock-holder can continue and eventually +releases the lock). + + Linus + +---- + +Reference information: +====================== + +For dynamic initialization, use spin_lock_init() or rwlock_init() as +appropriate:: + + spinlock_t xxx_lock; + rwlock_t xxx_rw_lock; + + static int __init xxx_init(void) + { + spin_lock_init(&xxx_lock); + rwlock_init(&xxx_rw_lock); + ... + } + + module_init(xxx_init); + +For static initialization, use DEFINE_SPINLOCK() / DEFINE_RWLOCK() or +__SPIN_LOCK_UNLOCKED() / __RW_LOCK_UNLOCKED() as appropriate. -- cgit v1.2.3