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/core-api/kref.rst | 323 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 323 insertions(+) create mode 100644 Documentation/core-api/kref.rst (limited to 'Documentation/core-api/kref.rst') diff --git a/Documentation/core-api/kref.rst b/Documentation/core-api/kref.rst new file mode 100644 index 000000000..c61eea6f1 --- /dev/null +++ b/Documentation/core-api/kref.rst @@ -0,0 +1,323 @@ +=================================================== +Adding reference counters (krefs) to kernel objects +=================================================== + +:Author: Corey Minyard +:Author: Thomas Hellstrom + +A lot of this was lifted from Greg Kroah-Hartman's 2004 OLS paper and +presentation on krefs, which can be found at: + + - http://www.kroah.com/linux/talks/ols_2004_kref_paper/Reprint-Kroah-Hartman-OLS2004.pdf + - http://www.kroah.com/linux/talks/ols_2004_kref_talk/ + +Introduction +============ + +krefs allow you to add reference counters to your objects. If you +have objects that are used in multiple places and passed around, and +you don't have refcounts, your code is almost certainly broken. If +you want refcounts, krefs are the way to go. + +To use a kref, add one to your data structures like:: + + struct my_data + { + . + . + struct kref refcount; + . + . + }; + +The kref can occur anywhere within the data structure. + +Initialization +============== + +You must initialize the kref after you allocate it. To do this, call +kref_init as so:: + + struct my_data *data; + + data = kmalloc(sizeof(*data), GFP_KERNEL); + if (!data) + return -ENOMEM; + kref_init(&data->refcount); + +This sets the refcount in the kref to 1. + +Kref rules +========== + +Once you have an initialized kref, you must follow the following +rules: + +1) If you make a non-temporary copy of a pointer, especially if + it can be passed to another thread of execution, you must + increment the refcount with kref_get() before passing it off:: + + kref_get(&data->refcount); + + If you already have a valid pointer to a kref-ed structure (the + refcount cannot go to zero) you may do this without a lock. + +2) When you are done with a pointer, you must call kref_put():: + + kref_put(&data->refcount, data_release); + + If this is the last reference to the pointer, the release + routine will be called. If the code never tries to get + a valid pointer to a kref-ed structure without already + holding a valid pointer, it is safe to do this without + a lock. + +3) If the code attempts to gain a reference to a kref-ed structure + without already holding a valid pointer, it must serialize access + where a kref_put() cannot occur during the kref_get(), and the + structure must remain valid during the kref_get(). + +For example, if you allocate some data and then pass it to another +thread to process:: + + void data_release(struct kref *ref) + { + struct my_data *data = container_of(ref, struct my_data, refcount); + kfree(data); + } + + void more_data_handling(void *cb_data) + { + struct my_data *data = cb_data; + . + . do stuff with data here + . + kref_put(&data->refcount, data_release); + } + + int my_data_handler(void) + { + int rv = 0; + struct my_data *data; + struct task_struct *task; + data = kmalloc(sizeof(*data), GFP_KERNEL); + if (!data) + return -ENOMEM; + kref_init(&data->refcount); + + kref_get(&data->refcount); + task = kthread_run(more_data_handling, data, "more_data_handling"); + if (task == ERR_PTR(-ENOMEM)) { + rv = -ENOMEM; + kref_put(&data->refcount, data_release); + goto out; + } + + . + . do stuff with data here + . + out: + kref_put(&data->refcount, data_release); + return rv; + } + +This way, it doesn't matter what order the two threads handle the +data, the kref_put() handles knowing when the data is not referenced +any more and releasing it. The kref_get() does not require a lock, +since we already have a valid pointer that we own a refcount for. The +put needs no lock because nothing tries to get the data without +already holding a pointer. + +In the above example, kref_put() will be called 2 times in both success +and error paths. This is necessary because the reference count got +incremented 2 times by kref_init() and kref_get(). + +Note that the "before" in rule 1 is very important. You should never +do something like:: + + task = kthread_run(more_data_handling, data, "more_data_handling"); + if (task == ERR_PTR(-ENOMEM)) { + rv = -ENOMEM; + goto out; + } else + /* BAD BAD BAD - get is after the handoff */ + kref_get(&data->refcount); + +Don't assume you know what you are doing and use the above construct. +First of all, you may not know what you are doing. Second, you may +know what you are doing (there are some situations where locking is +involved where the above may be legal) but someone else who doesn't +know what they are doing may change the code or copy the code. It's +bad style. Don't do it. + +There are some situations where you can optimize the gets and puts. +For instance, if you are done with an object and enqueuing it for +something else or passing it off to something else, there is no reason +to do a get then a put:: + + /* Silly extra get and put */ + kref_get(&obj->ref); + enqueue(obj); + kref_put(&obj->ref, obj_cleanup); + +Just do the enqueue. A comment about this is always welcome:: + + enqueue(obj); + /* We are done with obj, so we pass our refcount off + to the queue. DON'T TOUCH obj AFTER HERE! */ + +The last rule (rule 3) is the nastiest one to handle. Say, for +instance, you have a list of items that are each kref-ed, and you wish +to get the first one. You can't just pull the first item off the list +and kref_get() it. That violates rule 3 because you are not already +holding a valid pointer. You must add a mutex (or some other lock). +For instance:: + + static DEFINE_MUTEX(mutex); + static LIST_HEAD(q); + struct my_data + { + struct kref refcount; + struct list_head link; + }; + + static struct my_data *get_entry() + { + struct my_data *entry = NULL; + mutex_lock(&mutex); + if (!list_empty(&q)) { + entry = container_of(q.next, struct my_data, link); + kref_get(&entry->refcount); + } + mutex_unlock(&mutex); + return entry; + } + + static void release_entry(struct kref *ref) + { + struct my_data *entry = container_of(ref, struct my_data, refcount); + + list_del(&entry->link); + kfree(entry); + } + + static void put_entry(struct my_data *entry) + { + mutex_lock(&mutex); + kref_put(&entry->refcount, release_entry); + mutex_unlock(&mutex); + } + +The kref_put() return value is useful if you do not want to hold the +lock during the whole release operation. Say you didn't want to call +kfree() with the lock held in the example above (since it is kind of +pointless to do so). You could use kref_put() as follows:: + + static void release_entry(struct kref *ref) + { + /* All work is done after the return from kref_put(). */ + } + + static void put_entry(struct my_data *entry) + { + mutex_lock(&mutex); + if (kref_put(&entry->refcount, release_entry)) { + list_del(&entry->link); + mutex_unlock(&mutex); + kfree(entry); + } else + mutex_unlock(&mutex); + } + +This is really more useful if you have to call other routines as part +of the free operations that could take a long time or might claim the +same lock. Note that doing everything in the release routine is still +preferred as it is a little neater. + +The above example could also be optimized using kref_get_unless_zero() in +the following way:: + + static struct my_data *get_entry() + { + struct my_data *entry = NULL; + mutex_lock(&mutex); + if (!list_empty(&q)) { + entry = container_of(q.next, struct my_data, link); + if (!kref_get_unless_zero(&entry->refcount)) + entry = NULL; + } + mutex_unlock(&mutex); + return entry; + } + + static void release_entry(struct kref *ref) + { + struct my_data *entry = container_of(ref, struct my_data, refcount); + + mutex_lock(&mutex); + list_del(&entry->link); + mutex_unlock(&mutex); + kfree(entry); + } + + static void put_entry(struct my_data *entry) + { + kref_put(&entry->refcount, release_entry); + } + +Which is useful to remove the mutex lock around kref_put() in put_entry(), but +it's important that kref_get_unless_zero is enclosed in the same critical +section that finds the entry in the lookup table, +otherwise kref_get_unless_zero may reference already freed memory. +Note that it is illegal to use kref_get_unless_zero without checking its +return value. If you are sure (by already having a valid pointer) that +kref_get_unless_zero() will return true, then use kref_get() instead. + +Krefs and RCU +============= + +The function kref_get_unless_zero also makes it possible to use rcu +locking for lookups in the above example:: + + struct my_data + { + struct rcu_head rhead; + . + struct kref refcount; + . + . + }; + + static struct my_data *get_entry_rcu() + { + struct my_data *entry = NULL; + rcu_read_lock(); + if (!list_empty(&q)) { + entry = container_of(q.next, struct my_data, link); + if (!kref_get_unless_zero(&entry->refcount)) + entry = NULL; + } + rcu_read_unlock(); + return entry; + } + + static void release_entry_rcu(struct kref *ref) + { + struct my_data *entry = container_of(ref, struct my_data, refcount); + + mutex_lock(&mutex); + list_del_rcu(&entry->link); + mutex_unlock(&mutex); + kfree_rcu(entry, rhead); + } + + static void put_entry(struct my_data *entry) + { + kref_put(&entry->refcount, release_entry_rcu); + } + +But note that the struct kref member needs to remain in valid memory for a +rcu grace period after release_entry_rcu was called. That can be accomplished +by using kfree_rcu(entry, rhead) as done above, or by calling synchronize_rcu() +before using kfree, but note that synchronize_rcu() may sleep for a +substantial amount of time. -- cgit v1.2.3