aboutsummaryrefslogtreecommitdiff
path: root/fs/jffs2/README.Locking
diff options
context:
space:
mode:
authorLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
committerLibravatar Linus Torvalds <torvalds@linux-foundation.org>2023-02-21 18:24:12 -0800
commit5b7c4cabbb65f5c469464da6c5f614cbd7f730f2 (patch)
treecc5c2d0a898769fd59549594fedb3ee6f84e59a0 /fs/jffs2/README.Locking
downloadlinux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.tar.gz
linux-5b7c4cabbb65f5c469464da6c5f614cbd7f730f2.zip
Merge tag 'net-next-6.3' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-nextgrafted
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(). ...
Diffstat (limited to 'fs/jffs2/README.Locking')
-rw-r--r--fs/jffs2/README.Locking169
1 files changed, 169 insertions, 0 deletions
diff --git a/fs/jffs2/README.Locking b/fs/jffs2/README.Locking
new file mode 100644
index 000000000..8918ac905
--- /dev/null
+++ b/fs/jffs2/README.Locking
@@ -0,0 +1,169 @@
+
+ JFFS2 LOCKING DOCUMENTATION
+ ---------------------------
+
+This document attempts to describe the existing locking rules for
+JFFS2. It is not expected to remain perfectly up to date, but ought to
+be fairly close.
+
+
+ alloc_sem
+ ---------
+
+The alloc_sem is a per-filesystem mutex, used primarily to ensure
+contiguous allocation of space on the medium. It is automatically
+obtained during space allocations (jffs2_reserve_space()) and freed
+upon write completion (jffs2_complete_reservation()). Note that
+the garbage collector will obtain this right at the beginning of
+jffs2_garbage_collect_pass() and release it at the end, thereby
+preventing any other write activity on the file system during a
+garbage collect pass.
+
+When writing new nodes, the alloc_sem must be held until the new nodes
+have been properly linked into the data structures for the inode to
+which they belong. This is for the benefit of NAND flash - adding new
+nodes to an inode may obsolete old ones, and by holding the alloc_sem
+until this happens we ensure that any data in the write-buffer at the
+time this happens are part of the new node, not just something that
+was written afterwards. Hence, we can ensure the newly-obsoleted nodes
+don't actually get erased until the write-buffer has been flushed to
+the medium.
+
+With the introduction of NAND flash support and the write-buffer,
+the alloc_sem is also used to protect the wbuf-related members of the
+jffs2_sb_info structure. Atomically reading the wbuf_len member to see
+if the wbuf is currently holding any data is permitted, though.
+
+Ordering constraints: See f->sem.
+
+
+ File Mutex f->sem
+ ---------------------
+
+This is the JFFS2-internal equivalent of the inode mutex i->i_sem.
+It protects the contents of the jffs2_inode_info private inode data,
+including the linked list of node fragments (but see the notes below on
+erase_completion_lock), etc.
+
+The reason that the i_sem itself isn't used for this purpose is to
+avoid deadlocks with garbage collection -- the VFS will lock the i_sem
+before calling a function which may need to allocate space. The
+allocation may trigger garbage-collection, which may need to move a
+node belonging to the inode which was locked in the first place by the
+VFS. If the garbage collection code were to attempt to lock the i_sem
+of the inode from which it's garbage-collecting a physical node, this
+lead to deadlock, unless we played games with unlocking the i_sem
+before calling the space allocation functions.
+
+Instead of playing such games, we just have an extra internal
+mutex, which is obtained by the garbage collection code and also
+by the normal file system code _after_ allocation of space.
+
+Ordering constraints:
+
+ 1. Never attempt to allocate space or lock alloc_sem with
+ any f->sem held.
+ 2. Never attempt to lock two file mutexes in one thread.
+ No ordering rules have been made for doing so.
+ 3. Never lock a page cache page with f->sem held.
+
+
+ erase_completion_lock spinlock
+ ------------------------------
+
+This is used to serialise access to the eraseblock lists, to the
+per-eraseblock lists of physical jffs2_raw_node_ref structures, and
+(NB) the per-inode list of physical nodes. The latter is a special
+case - see below.
+
+As the MTD API no longer permits erase-completion callback functions
+to be called from bottom-half (timer) context (on the basis that nobody
+ever actually implemented such a thing), it's now sufficient to use
+a simple spin_lock() rather than spin_lock_bh().
+
+Note that the per-inode list of physical nodes (f->nodes) is a special
+case. Any changes to _valid_ nodes (i.e. ->flash_offset & 1 == 0) in
+the list are protected by the file mutex f->sem. But the erase code
+may remove _obsolete_ nodes from the list while holding only the
+erase_completion_lock. So you can walk the list only while holding the
+erase_completion_lock, and can drop the lock temporarily mid-walk as
+long as the pointer you're holding is to a _valid_ node, not an
+obsolete one.
+
+The erase_completion_lock is also used to protect the c->gc_task
+pointer when the garbage collection thread exits. The code to kill the
+GC thread locks it, sends the signal, then unlocks it - while the GC
+thread itself locks it, zeroes c->gc_task, then unlocks on the exit path.
+
+
+ inocache_lock spinlock
+ ----------------------
+
+This spinlock protects the hashed list (c->inocache_list) of the
+in-core jffs2_inode_cache objects (each inode in JFFS2 has the
+correspondent jffs2_inode_cache object). So, the inocache_lock
+has to be locked while walking the c->inocache_list hash buckets.
+
+This spinlock also covers allocation of new inode numbers, which is
+currently just '++->highest_ino++', but might one day get more complicated
+if we need to deal with wrapping after 4 milliard inode numbers are used.
+
+Note, the f->sem guarantees that the correspondent jffs2_inode_cache
+will not be removed. So, it is allowed to access it without locking
+the inocache_lock spinlock.
+
+Ordering constraints:
+
+ If both erase_completion_lock and inocache_lock are needed, the
+ c->erase_completion has to be acquired first.
+
+
+ erase_free_sem
+ --------------
+
+This mutex is only used by the erase code which frees obsolete node
+references and the jffs2_garbage_collect_deletion_dirent() function.
+The latter function on NAND flash must read _obsolete_ nodes to
+determine whether the 'deletion dirent' under consideration can be
+discarded or whether it is still required to show that an inode has
+been unlinked. Because reading from the flash may sleep, the
+erase_completion_lock cannot be held, so an alternative, more
+heavyweight lock was required to prevent the erase code from freeing
+the jffs2_raw_node_ref structures in question while the garbage
+collection code is looking at them.
+
+Suggestions for alternative solutions to this problem would be welcomed.
+
+
+ wbuf_sem
+ --------
+
+This read/write semaphore protects against concurrent access to the
+write-behind buffer ('wbuf') used for flash chips where we must write
+in blocks. It protects both the contents of the wbuf and the metadata
+which indicates which flash region (if any) is currently covered by
+the buffer.
+
+Ordering constraints:
+ Lock wbuf_sem last, after the alloc_sem or and f->sem.
+
+
+ c->xattr_sem
+ ------------
+
+This read/write semaphore protects against concurrent access to the
+xattr related objects which include stuff in superblock and ic->xref.
+In read-only path, write-semaphore is too much exclusion. It's enough
+by read-semaphore. But you must hold write-semaphore when updating,
+creating or deleting any xattr related object.
+
+Once xattr_sem released, there would be no assurance for the existence
+of those objects. Thus, a series of processes is often required to retry,
+when updating such a object is necessary under holding read semaphore.
+For example, do_jffs2_getxattr() holds read-semaphore to scan xref and
+xdatum at first. But it retries this process with holding write-semaphore
+after release read-semaphore, if it's necessary to load name/value pair
+from medium.
+
+Ordering constraints:
+ Lock xattr_sem last, after the alloc_sem.