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, 192 insertions, 0 deletions

diff --git a/Documentation/bpf/map_xskmap.rst b/Documentation/bpf/map_xskmap.rst
new file mode 100644
index 000000000..dc143edd9
--- /dev/null
+++ b/Documentation/bpf/map_xskmap.rst
@@ -0,0 +1,192 @@
+.. SPDX-License-Identifier: GPL-2.0-only
+.. Copyright (C) 2022 Red Hat, Inc.
+
+===================
+BPF_MAP_TYPE_XSKMAP
+===================
+
+.. note::
+   - ``BPF_MAP_TYPE_XSKMAP`` was introduced in kernel version 4.18
+
+The ``BPF_MAP_TYPE_XSKMAP`` is used as a backend map for XDP BPF helper
+call ``bpf_redirect_map()`` and ``XDP_REDIRECT`` action, like 'devmap' and 'cpumap'.
+This map type redirects raw XDP frames to `AF_XDP`_ sockets (XSKs), a new type of
+address family in the kernel that allows redirection of frames from a driver to
+user space without having to traverse the full network stack. An AF_XDP socket
+binds to a single netdev queue. A mapping of XSKs to queues is shown below:
+
+.. code-block:: none
+
+    +---------------------------------------------------+
+    |     xsk A      |     xsk B       |      xsk C     |<---+ User space
+    =========================================================|==========
+    |    Queue 0     |     Queue 1     |     Queue 2    |    |  Kernel
+    +---------------------------------------------------+    |
+    |                  Netdev eth0                      |    |
+    +---------------------------------------------------+    |
+    |                            +=============+        |    |
+    |                            | key |  xsk  |        |    |
+    |  +---------+               +=============+        |    |
+    |  |         |               |  0  | xsk A |        |    |
+    |  |         |               +-------------+        |    |
+    |  |         |               |  1  | xsk B |        |    |
+    |  | BPF     |-- redirect -->+-------------+-------------+
+    |  | prog    |               |  2  | xsk C |        |
+    |  |         |               +-------------+        |
+    |  |         |                                      |
+    |  |         |                                      |
+    |  +---------+                                      |
+    |                                                   |
+    +---------------------------------------------------+
+
+.. note::
+    An AF_XDP socket that is bound to a certain <netdev/queue_id> will *only*
+    accept XDP frames from that <netdev/queue_id>. If an XDP program tries to redirect
+    from a <netdev/queue_id> other than what the socket is bound to, the frame will
+    not be received on the socket.
+
+Typically an XSKMAP is created per netdev. This map contains an array of XSK File
+Descriptors (FDs). The number of array elements is typically set or adjusted using
+the ``max_entries`` map parameter. For AF_XDP ``max_entries`` is equal to the number
+of queues supported by the netdev.
+
+.. note::
+    Both the map key and map value size must be 4 bytes.
+
+Usage
+=====
+
+Kernel BPF
+----------
+bpf_redirect_map()
+^^^^^^^^^^^^^^^^^^
+.. code-block:: c
+
+    long bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)
+
+Redirect the packet to the endpoint referenced by ``map`` at index ``key``.
+For ``BPF_MAP_TYPE_XSKMAP`` this map contains references to XSK FDs
+for sockets attached to a netdev's queues.
+
+.. note::
+    If the map is empty at an index, the packet is dropped. This means that it is
+    necessary to have an XDP program loaded with at least one XSK in the
+    XSKMAP to be able to get any traffic to user space through the socket.
+
+bpf_map_lookup_elem()
+^^^^^^^^^^^^^^^^^^^^^
+.. code-block:: c
+
+    void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
+
+XSK entry references of type ``struct xdp_sock *`` can be retrieved using the
+``bpf_map_lookup_elem()`` helper.
+
+User space
+----------
+.. note::
+    XSK entries can only be updated/deleted from user space and not from
+    a BPF program. Trying to call these functions from a kernel BPF program will
+    result in the program failing to load and a verifier warning.
+
+bpf_map_update_elem()
+^^^^^^^^^^^^^^^^^^^^^
+.. code-block:: c
+
+	int bpf_map_update_elem(int fd, const void *key, const void *value, __u64 flags)
+
+XSK entries can be added or updated using the ``bpf_map_update_elem()``
+helper. The ``key`` parameter is equal to the queue_id of the queue the XSK
+is attaching to. And the ``value`` parameter is the FD value of that socket.
+
+Under the hood, the XSKMAP update function uses the XSK FD value to retrieve the
+associated ``struct xdp_sock`` instance.
+
+The flags argument can be one of the following:
+
+- BPF_ANY: Create a new element or update an existing element.
+- BPF_NOEXIST: Create a new element only if it did not exist.
+- BPF_EXIST: Update an existing element.
+
+bpf_map_lookup_elem()
+^^^^^^^^^^^^^^^^^^^^^
+.. code-block:: c
+
+    int bpf_map_lookup_elem(int fd, const void *key, void *value)
+
+Returns ``struct xdp_sock *`` or negative error in case of failure.
+
+bpf_map_delete_elem()
+^^^^^^^^^^^^^^^^^^^^^
+.. code-block:: c
+
+    int bpf_map_delete_elem(int fd, const void *key)
+
+XSK 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.
+
+.. note::
+    When `libxdp`_ deletes an XSK it also removes the associated socket
+    entry from the XSKMAP.
+
+Examples
+========
+Kernel
+------
+
+The following code snippet shows how to declare a ``BPF_MAP_TYPE_XSKMAP`` called
+``xsks_map`` and how to redirect packets to an XSK.
+
+.. code-block:: c
+
+	struct {
+		__uint(type, BPF_MAP_TYPE_XSKMAP);
+		__type(key, __u32);
+		__type(value, __u32);
+		__uint(max_entries, 64);
+	} xsks_map SEC(".maps");
+
+
+	SEC("xdp")
+	int xsk_redir_prog(struct xdp_md *ctx)
+	{
+		__u32 index = ctx->rx_queue_index;
+
+		if (bpf_map_lookup_elem(&xsks_map, &index))
+			return bpf_redirect_map(&xsks_map, index, 0);
+		return XDP_PASS;
+	}
+
+User space
+----------
+
+The following code snippet shows how to update an XSKMAP with an XSK entry.
+
+.. code-block:: c
+
+	int update_xsks_map(struct bpf_map *xsks_map, int queue_id, int xsk_fd)
+	{
+		int ret;
+
+		ret = bpf_map_update_elem(bpf_map__fd(xsks_map), &queue_id, &xsk_fd, 0);
+		if (ret < 0)
+			fprintf(stderr, "Failed to update xsks_map: %s\n", strerror(errno));
+
+		return ret;
+	}
+
+For an example on how create AF_XDP sockets, please see the AF_XDP-example and
+AF_XDP-forwarding programs in the `bpf-examples`_ directory in the `libxdp`_ repository.
+For a detailed explanation of the AF_XDP interface please see:
+
+- `libxdp-readme`_.
+- `AF_XDP`_ kernel documentation.
+
+.. note::
+    The most comprehensive resource for using XSKMAPs and AF_XDP is `libxdp`_.
+
+.. _libxdp: https://github.com/xdp-project/xdp-tools/tree/master/lib/libxdp
+.. _AF_XDP: https://www.kernel.org/doc/html/latest/networking/af_xdp.html
+.. _bpf-examples: https://github.com/xdp-project/bpf-examples
+.. _libxdp-readme: https://github.com/xdp-project/xdp-tools/tree/master/lib/libxdp#using-af_xdp-sockets