From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fixes from Steven Rostedt: - Fix error output of boot instance creation failure Currently if a boot instance creation fails, instead of printing out the name of the instance that failed, it prints "(null)". That is because it prints "cur_str" that had already been processed by strsep(). Print the saved name instead. While at it, print the error code of the failure. - Fix use-after-free for same named historgrams Histograms can be named so that they can be used in multiple events. But if the named histogram has a variable attached, the second event that uses the named histogram which duplicates it and needs to free the original after duplication leaves the old variable in place and still visible. If another histogram uses than variable, it will use the stale one which will try to reference the freed duplicate histogram and crash the kernel. Free the duplicate variables along with the duplicated histogram data. - Check return value of kthread_run() in event self test The events self tests uses a kthread for testing but does not check if it succeeded in creating a kthread. If the kthread creation were to fail, the code will still try to call kthread_stop() on the error returned. - Fix race between reading trace_pipe and updating subbuffer size If a user is reading the trace_pipe file at the same time they update the ring buffer sub-buffer size, can cause the trace_pipe read to read stale data. Add trace_access_lock() around updating the ring buffer sub-buffer size. - Fix eventfs_inode on failure path in creation of the events directory In the creation of the "events" directory, if after allocating the eventfs_inode a failure is detected, it calls cleanup_ei() which calls free_ei(). The free_ei() will test if eventfs_inode being freed has no children. It is a bug if it does. But on the failure case of the creation of the "events" directory, the children lists have not yet been initialized and the free will trigger a warning because list_empty() on an uninitialized list returns false. Move the initialization into init_ei() where it makes more sense and makes sure that a created eventfs_inode has its lists initialized upon creation. - Check return value of kthread_run() in ftrace direct sample code The sample code that shows how to use the ftrace direct calls does not test the return of kthread_run() to see if it succeeds. Return a failure if the kthread_run() doesn't succeed. - Clear user events state on fork in case of alloc failure On fork, the child gets a pointer to the parent's user events state. It makes a copy of it then updates the child's pointer to it. But if the allocation fails, the duplication function leaves the child with a pointer to its parent's descriptor. When the child cleans up its data, it will free the parent's descriptor while the parent is still using it. In the duplication function, set the child's user_event_mm to NULL before testing if the allocation succeeded, and when it exits it will not free the parent's descriptor. - Fix retry exhaustion in simple ring buffer reader swap simple_ring_buffer_swap_reader_page() starts with retry set to 8 and post-decrements it only after a failed link replacement. On the final attempt, a successful replacement leaves retry at zero, while a failed replacement leaves it at -1. But the check for success expects the retry value to be non-zero and exits with an error on zero. This is the opposite result. Fix it. - Fail nicely when the remote swap_reader_page() returns an error Currently, if the swap_reader_page() of a remote buffer fails, it triggers a WARN_ON_ONCE() and continues normally. Instead, have it exit with an error and a pr_warn() print instead of a full WARNING. * tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: ring-buffer: Stop remote reader update when page swap fails tracing: Fix retry exhaustion in simple ring buffer reader swap tracing/user_events: Clear copied tracing state before fork duplication samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify eventfs: Initialize ei->children and ei->list in init_ei() tracing: Fix use-after-free in trace_pipe read on sub-buffer order change tracing: Fix crash passing ERR_PTR to kthread_stop() tracing: Fix use-after-free with same-name named triggers tracing: Fix logged instance name on creation failure --- Documentation/driver-api/edac.rst | 298 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 298 insertions(+) create mode 100644 Documentation/driver-api/edac.rst (limited to 'Documentation/driver-api/edac.rst') diff --git a/Documentation/driver-api/edac.rst b/Documentation/driver-api/edac.rst new file mode 100644 index 000000000..f4f044b95 --- /dev/null +++ b/Documentation/driver-api/edac.rst @@ -0,0 +1,298 @@ +Error Detection And Correction (EDAC) Devices +============================================= + +Main Concepts used at the EDAC subsystem +---------------------------------------- + +There are several things to be aware of that aren't at all obvious, like +*sockets, *socket sets*, *banks*, *rows*, *chip-select rows*, *channels*, +etc... + +These are some of the many terms that are thrown about that don't always +mean what people think they mean (Inconceivable!). In the interest of +creating a common ground for discussion, terms and their definitions +will be established. + +* Memory devices + +The individual DRAM chips on a memory stick. These devices commonly +output 4 and 8 bits each (x4, x8). Grouping several of these in parallel +provides the number of bits that the memory controller expects: +typically 72 bits, in order to provide 64 bits + 8 bits of ECC data. + +* Memory Stick + +A printed circuit board that aggregates multiple memory devices in +parallel. In general, this is the Field Replaceable Unit (FRU) which +gets replaced, in the case of excessive errors. Most often it is also +called DIMM (Dual Inline Memory Module). + +* Memory Socket + +A physical connector on the motherboard that accepts a single memory +stick. Also called as "slot" on several datasheets. + +* Channel + +A memory controller channel, responsible to communicate with a group of +DIMMs. Each channel has its own independent control (command) and data +bus, and can be used independently or grouped with other channels. + +* Branch + +It is typically the highest hierarchy on a Fully-Buffered DIMM memory +controller. Typically, it contains two channels. Two channels at the +same branch can be used in single mode or in lockstep mode. When +lockstep is enabled, the cacheline is doubled, but it generally brings +some performance penalty. Also, it is generally not possible to point to +just one memory stick when an error occurs, as the error correction code +is calculated using two DIMMs instead of one. Due to that, it is capable +of correcting more errors than on single mode. + +* Single-channel + +The data accessed by the memory controller is contained into one dimm +only. E. g. if the data is 64 bits-wide, the data flows to the CPU using +one 64 bits parallel access. Typically used with SDR, DDR, DDR2 and DDR3 +memories. FB-DIMM and RAMBUS use a different concept for channel, so +this concept doesn't apply there. + +* Double-channel + +The data size accessed by the memory controller is interlaced into two +dimms, accessed at the same time. E. g. if the DIMM is 64 bits-wide (72 +bits with ECC), the data flows to the CPU using a 128 bits parallel +access. + +* Chip-select row + +This is the name of the DRAM signal used to select the DRAM ranks to be +accessed. Common chip-select rows for single channel are 64 bits, for +dual channel 128 bits. It may not be visible by the memory controller, +as some DIMM types have a memory buffer that can hide direct access to +it from the Memory Controller. + +* Single-Ranked stick + +A Single-ranked stick has 1 chip-select row of memory. Motherboards +commonly drive two chip-select pins to a memory stick. A single-ranked +stick, will occupy only one of those rows. The other will be unused. + +.. _doubleranked: + +* Double-Ranked stick + +A double-ranked stick has two chip-select rows which access different +sets of memory devices. The two rows cannot be accessed concurrently. + +* Double-sided stick + +**DEPRECATED TERM**, see :ref:`Double-Ranked stick `. + +A double-sided stick has two chip-select rows which access different sets +of memory devices. The two rows cannot be accessed concurrently. +"Double-sided" is irrespective of the memory devices being mounted on +both sides of the memory stick. + +* Socket set + +All of the memory sticks that are required for a single memory access or +all of the memory sticks spanned by a chip-select row. A single socket +set has two chip-select rows and if double-sided sticks are used these +will occupy those chip-select rows. + +* Bank + +This term is avoided because it is unclear when needing to distinguish +between chip-select rows and socket sets. + +* High Bandwidth Memory (HBM) + +HBM is a new memory type with low power consumption and ultra-wide +communication lanes. It uses vertically stacked memory chips (DRAM dies) +interconnected by microscopic wires called "through-silicon vias," or +TSVs. + +Several stacks of HBM chips connect to the CPU or GPU through an ultra-fast +interconnect called the "interposer". Therefore, HBM's characteristics +are nearly indistinguishable from on-chip integrated RAM. + +Memory Controllers +------------------ + +Most of the EDAC core is focused on doing Memory Controller error detection. +The :c:func:`edac_mc_alloc`. It uses internally the struct ``mem_ctl_info`` +to describe the memory controllers, with is an opaque struct for the EDAC +drivers. Only the EDAC core is allowed to touch it. + +.. kernel-doc:: include/linux/edac.h + +.. kernel-doc:: drivers/edac/edac_mc.h + +PCI Controllers +--------------- + +The EDAC subsystem provides a mechanism to handle PCI controllers by calling +the :c:func:`edac_pci_alloc_ctl_info`. It will use the struct +:c:type:`edac_pci_ctl_info` to describe the PCI controllers. + +.. kernel-doc:: drivers/edac/edac_pci.h + +EDAC Blocks +----------- + +The EDAC subsystem also provides a generic mechanism to report errors on +other parts of the hardware via :c:func:`edac_device_alloc_ctl_info` function. + +The structures :c:type:`edac_dev_sysfs_block_attribute`, +:c:type:`edac_device_block`, :c:type:`edac_device_instance` and +:c:type:`edac_device_ctl_info` provide a generic or abstract 'edac_device' +representation at sysfs. + +This set of structures and the code that implements the APIs for the same, provide for registering EDAC type devices which are NOT standard memory or +PCI, like: + +- CPU caches (L1 and L2) +- DMA engines +- Core CPU switches +- Fabric switch units +- PCIe interface controllers +- other EDAC/ECC type devices that can be monitored for + errors, etc. + +It allows for a 2 level set of hierarchy. + +For example, a cache could be composed of L1, L2 and L3 levels of cache. +Each CPU core would have its own L1 cache, while sharing L2 and maybe L3 +caches. On such case, those can be represented via the following sysfs +nodes:: + + /sys/devices/system/edac/.. + + pci/ + mc/ + cpu/cpu0/.. + /L1-cache/ce_count + /ue_count + /L2-cache/ce_count + /ue_count + cpu/cpu1/.. + /L1-cache/ce_count + /ue_count + /L2-cache/ce_count + /ue_count + ... + + the L1 and L2 directories would be "edac_device_block's" + +.. kernel-doc:: drivers/edac/edac_device.h + + +Heterogeneous system support +---------------------------- + +An AMD heterogeneous system is built by connecting the data fabrics of +both CPUs and GPUs via custom xGMI links. Thus, the data fabric on the +GPU nodes can be accessed the same way as the data fabric on CPU nodes. + +The MI200 accelerators are data center GPUs. They have 2 data fabrics, +and each GPU data fabric contains four Unified Memory Controllers (UMC). +Each UMC contains eight channels. Each UMC channel controls one 128-bit +HBM2e (2GB) channel (equivalent to 8 X 2GB ranks). This creates a total +of 4096-bits of DRAM data bus. + +While the UMC is interfacing a 16GB (8high X 2GB DRAM) HBM stack, each UMC +channel is interfacing 2GB of DRAM (represented as rank). + +Memory controllers on AMD GPU nodes can be represented in EDAC thusly: + + GPU DF / GPU Node -> EDAC MC + GPU UMC -> EDAC CSROW + GPU UMC channel -> EDAC CHANNEL + +For example: a heterogeneous system with 1 AMD CPU is connected to +4 MI200 (Aldebaran) GPUs using xGMI. + +Some more heterogeneous hardware details: + +- The CPU UMC (Unified Memory Controller) is mostly the same as the GPU UMC. + They have chip selects (csrows) and channels. However, the layouts are different + for performance, physical layout, or other reasons. +- CPU UMCs use 1 channel, In this case UMC = EDAC channel. This follows the + marketing speak. CPU has X memory channels, etc. +- CPU UMCs use up to 4 chip selects, So UMC chip select = EDAC CSROW. +- GPU UMCs use 1 chip select, So UMC = EDAC CSROW. +- GPU UMCs use 8 channels, So UMC channel = EDAC channel. + +The EDAC subsystem provides a mechanism to handle AMD heterogeneous +systems by calling system specific ops for both CPUs and GPUs. + +AMD GPU nodes are enumerated in sequential order based on the PCI +hierarchy, and the first GPU node is assumed to have a Node ID value +following those of the CPU nodes after latter are fully populated:: + + $ ls /sys/devices/system/edac/mc/ + mc0 - CPU MC node 0 + mc1 | + mc2 |- GPU card[0] => node 0(mc1), node 1(mc2) + mc3 | + mc4 |- GPU card[1] => node 0(mc3), node 1(mc4) + mc5 | + mc6 |- GPU card[2] => node 0(mc5), node 1(mc6) + mc7 | + mc8 |- GPU card[3] => node 0(mc7), node 1(mc8) + +For example, a heterogeneous system with one AMD CPU is connected to +four MI200 (Aldebaran) GPUs using xGMI. This topology can be represented +via the following sysfs entries:: + + /sys/devices/system/edac/mc/.. + + CPU # CPU node + ├── mc 0 + + GPU Nodes are enumerated sequentially after CPU nodes have been populated + GPU card 1 # Each MI200 GPU has 2 nodes/mcs + ├── mc 1 # GPU node 0 == mc1, Each MC node has 4 UMCs/CSROWs + │   ├── csrow 0 # UMC 0 + │   │   ├── channel 0 # Each UMC has 8 channels + │   │   ├── channel 1 # size of each channel is 2 GB, so each UMC has 16 GB + │   │   ├── channel 2 + │   │   ├── channel 3 + │   │   ├── channel 4 + │   │   ├── channel 5 + │   │   ├── channel 6 + │   │   ├── channel 7 + │   ├── csrow 1 # UMC 1 + │   │   ├── channel 0 + │   │   ├── .. + │   │   ├── channel 7 + │   ├── .. .. + │   ├── csrow 3 # UMC 3 + │   │   ├── channel 0 + │   │   ├── .. + │   │   ├── channel 7 + │   ├── rank 0 + │   ├── .. .. + │   ├── rank 31 # total 32 ranks/dimms from 4 UMCs + ├ + ├── mc 2 # GPU node 1 == mc2 + │   ├── .. # each GPU has total 64 GB + + GPU card 2 + ├── mc 3 + │   ├── .. + ├── mc 4 + │   ├── .. + + GPU card 3 + ├── mc 5 + │   ├── .. + ├── mc 6 + │   ├── .. + + GPU card 4 + ├── mc 7 + │   ├── .. + ├── mc 8 + │   ├── .. -- cgit v1.3.1