Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

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

1 files changed, 265 insertions, 0 deletions

diff --git a/Documentation/bpf/map_hash.rst b/Documentation/bpf/map_hash.rst
new file mode 100644
index 000000000..8606bf958
--- /dev/null
+++ b/Documentation/bpf/map_hash.rst
@@ -0,0 +1,265 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+.. Copyright (C) 2022 Red Hat, Inc.
+.. Copyright (C) 2022-2023 Isovalent, Inc.
+
+===============================================
+BPF_MAP_TYPE_HASH, with PERCPU and LRU Variants
+===============================================
+
+.. note::
+   - ``BPF_MAP_TYPE_HASH`` was introduced in kernel version 3.19
+   - ``BPF_MAP_TYPE_PERCPU_HASH`` was introduced in version 4.6
+   - Both ``BPF_MAP_TYPE_LRU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH``
+     were introduced in version 4.10
+
+``BPF_MAP_TYPE_HASH`` and ``BPF_MAP_TYPE_PERCPU_HASH`` provide general
+purpose hash map storage. Both the key and the value can be structs,
+allowing for composite keys and values.
+
+The kernel is responsible for allocating and freeing key/value pairs, up
+to the max_entries limit that you specify. Hash maps use pre-allocation
+of hash table elements by default. The ``BPF_F_NO_PREALLOC`` flag can be
+used to disable pre-allocation when it is too memory expensive.
+
+``BPF_MAP_TYPE_PERCPU_HASH`` provides a separate value slot per
+CPU. The per-cpu values are stored internally in an array.
+
+The ``BPF_MAP_TYPE_LRU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH``
+variants add LRU semantics to their respective hash tables. An LRU hash
+will automatically evict the least recently used entries when the hash
+table reaches capacity. An LRU hash maintains an internal LRU list that
+is used to select elements for eviction. This internal LRU list is
+shared across CPUs but it is possible to request a per CPU LRU list with
+the ``BPF_F_NO_COMMON_LRU`` flag when calling ``bpf_map_create``.  The
+following table outlines the properties of LRU maps depending on the a
+map type and the flags used to create the map.
+
+======================== ========================= ================================
+Flag                     ``BPF_MAP_TYPE_LRU_HASH`` ``BPF_MAP_TYPE_LRU_PERCPU_HASH``
+======================== ========================= ================================
+**BPF_F_NO_COMMON_LRU**  Per-CPU LRU, global map   Per-CPU LRU, per-cpu map
+**!BPF_F_NO_COMMON_LRU** Global LRU, global map    Global LRU, per-cpu map
+======================== ========================= ================================
+
+Usage
+=====
+
+Kernel BPF
+----------
+
+bpf_map_update_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   long bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
+
+Hash entries can be added or updated using the ``bpf_map_update_elem()``
+helper. This helper replaces existing elements atomically. The ``flags``
+parameter can be used to control the update behaviour:
+
+- ``BPF_ANY`` will create a new element or update an existing element
+- ``BPF_NOEXIST`` will create a new element only if one did not already
+  exist
+- ``BPF_EXIST`` will update an existing element
+
+``bpf_map_update_elem()`` returns 0 on success, or negative error in
+case of failure.
+
+bpf_map_lookup_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
+
+Hash entries can be retrieved using the ``bpf_map_lookup_elem()``
+helper. This helper returns a pointer to the value associated with
+``key``, or ``NULL`` if no entry was found.
+
+bpf_map_delete_elem()
+~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   long bpf_map_delete_elem(struct bpf_map *map, const void *key)
+
+Hash entries can be deleted using the ``bpf_map_delete_elem()``
+helper. This helper will return 0 on success, or negative error in case
+of failure.
+
+Per CPU Hashes
+--------------
+
+For ``BPF_MAP_TYPE_PERCPU_HASH`` and ``BPF_MAP_TYPE_LRU_PERCPU_HASH``
+the ``bpf_map_update_elem()`` and ``bpf_map_lookup_elem()`` helpers
+automatically access the hash slot for the current CPU.
+
+bpf_map_lookup_percpu_elem()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   void *bpf_map_lookup_percpu_elem(struct bpf_map *map, const void *key, u32 cpu)
+
+The ``bpf_map_lookup_percpu_elem()`` helper can be used to lookup the
+value in the hash slot for a specific CPU. Returns value associated with
+``key`` on ``cpu`` , or ``NULL`` if no entry was found or ``cpu`` is
+invalid.
+
+Concurrency
+-----------
+
+Values stored in ``BPF_MAP_TYPE_HASH`` can be accessed concurrently by
+programs running on different CPUs.  Since Kernel version 5.1, the BPF
+infrastructure provides ``struct bpf_spin_lock`` to synchronise access.
+See ``tools/testing/selftests/bpf/progs/test_spin_lock.c``.
+
+Userspace
+---------
+
+bpf_map_get_next_key()
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: c
+
+   int bpf_map_get_next_key(int fd, const void *cur_key, void *next_key)
+
+In userspace, it is possible to iterate through the keys of a hash using
+libbpf's ``bpf_map_get_next_key()`` function. The first key can be fetched by
+calling ``bpf_map_get_next_key()`` with ``cur_key`` set to
+``NULL``. Subsequent calls will fetch the next key that follows the
+current key. ``bpf_map_get_next_key()`` returns 0 on success, -ENOENT if
+cur_key is the last key in the hash, or negative error in case of
+failure.
+
+Note that if ``cur_key`` gets deleted then ``bpf_map_get_next_key()``
+will instead return the *first* key in the hash table which is
+undesirable. It is recommended to use batched lookup if there is going
+to be key deletion intermixed with ``bpf_map_get_next_key()``.
+
+Examples
+========
+
+Please see the ``tools/testing/selftests/bpf`` directory for functional
+examples.  The code snippets below demonstrates API usage.
+
+This example shows how to declare an LRU Hash with a struct key and a
+struct value.
+
+.. code-block:: c
+
+    #include <linux/bpf.h>
+    #include <bpf/bpf_helpers.h>
+
+    struct key {
+        __u32 srcip;
+    };
+
+    struct value {
+        __u64 packets;
+        __u64 bytes;
+    };
+
+    struct {
+            __uint(type, BPF_MAP_TYPE_LRU_HASH);
+            __uint(max_entries, 32);
+            __type(key, struct key);
+            __type(value, struct value);
+    } packet_stats SEC(".maps");
+
+This example shows how to create or update hash values using atomic
+instructions:
+
+.. code-block:: c
+
+    static void update_stats(__u32 srcip, int bytes)
+    {
+            struct key key = {
+                    .srcip = srcip,
+            };
+            struct value *value = bpf_map_lookup_elem(&packet_stats, &key);
+
+            if (value) {
+                    __sync_fetch_and_add(&value->packets, 1);
+                    __sync_fetch_and_add(&value->bytes, bytes);
+            } else {
+                    struct value newval = { 1, bytes };
+
+                    bpf_map_update_elem(&packet_stats, &key, &newval, BPF_NOEXIST);
+            }
+    }
+
+Userspace walking the map elements from the map declared above:
+
+.. code-block:: c
+
+    #include <bpf/libbpf.h>
+    #include <bpf/bpf.h>
+
+    static void walk_hash_elements(int map_fd)
+    {
+            struct key *cur_key = NULL;
+            struct key next_key;
+            struct value value;
+            int err;
+
+            for (;;) {
+                    err = bpf_map_get_next_key(map_fd, cur_key, &next_key);
+                    if (err)
+                            break;
+
+                    bpf_map_lookup_elem(map_fd, &next_key, &value);
+
+                    // Use key and value here
+
+                    cur_key = &next_key;
+            }
+    }
+
+Internals
+=========
+
+This section of the document is targeted at Linux developers and describes
+aspects of the map implementations that are not considered stable ABI. The
+following details are subject to change in future versions of the kernel.
+
+``BPF_MAP_TYPE_LRU_HASH`` and variants
+--------------------------------------
+
+Updating elements in LRU maps may trigger eviction behaviour when the capacity
+of the map is reached. There are various steps that the update algorithm
+attempts in order to enforce the LRU property which have increasing impacts on
+other CPUs involved in the following operation attempts:
+
+- Attempt to use CPU-local state to batch operations
+- Attempt to fetch ``target_free`` free nodes from global lists
+- Attempt to pull any node from a global list and remove it from the hashmap
+- Attempt to pull any node from any CPU's list and remove it from the hashmap
+
+The number of nodes to borrow from the global list in a batch, ``target_free``,
+depends on the size of the map. Larger batch size reduces lock contention, but
+may also exhaust the global structure. The value is computed at map init to
+avoid exhaustion, by limiting aggregate reservation by all CPUs to half the map
+size. With a minimum of a single element and maximum budget of 128 at a time.
+
+This algorithm is described visually in the following diagram. See the
+description in commit 3a08c2fd7634 ("bpf: LRU List") for a full explanation of
+the corresponding operations:
+
+.. kernel-figure::  map_lru_hash_update.dot
+   :alt:    Diagram outlining the LRU eviction steps taken during map update.
+
+   LRU hash eviction during map update for ``BPF_MAP_TYPE_LRU_HASH`` and
+   variants. See the dot file source for kernel function name code references.
+
+Map updates start from the oval in the top right "begin ``bpf_map_update()``"
+and progress through the graph towards the bottom where the result may be
+either a successful update or a failure with various error codes. The key in
+the top right provides indicators for which locks may be involved in specific
+operations. This is intended as a visual hint for reasoning about how map
+contention may impact update operations, though the map type and flags may
+impact the actual contention on those locks, based on the logic described in
+the table above. For instance, if the map is created with type
+``BPF_MAP_TYPE_LRU_PERCPU_HASH`` and flags ``BPF_F_NO_COMMON_LRU`` then all map
+properties would be per-cpu.