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, 198 insertions, 0 deletions

diff --git a/Documentation/trace/fprobe.rst b/Documentation/trace/fprobe.rst
new file mode 100644
index 000000000..46dd46a97
--- /dev/null
+++ b/Documentation/trace/fprobe.rst
@@ -0,0 +1,198 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==================================
+Fprobe - Function entry/exit probe
+==================================
+
+.. Author: Masami Hiramatsu <mhiramat@kernel.org>
+
+Introduction
+============
+
+Fprobe is a function entry/exit probe based on the function-graph tracing
+feature in ftrace.
+Instead of tracing all functions, if you want to attach callbacks on specific
+function entry and exit, similar to the kprobes and kretprobes, you can
+use fprobe. Compared with kprobes and kretprobes, fprobe gives faster
+instrumentation for multiple functions with single handler. This document
+describes how to use fprobe.
+
+The usage of fprobe
+===================
+
+The fprobe is a wrapper of ftrace (+ kretprobe-like return callback) to
+attach callbacks to multiple function entry and exit. User needs to set up
+the `struct fprobe` and pass it to `register_fprobe()`.
+
+Typically, `fprobe` data structure is initialized with the `entry_handler`
+and/or `exit_handler` as below.
+
+.. code-block:: c
+
+ struct fprobe fp = {
+        .entry_handler  = my_entry_callback,
+        .exit_handler   = my_exit_callback,
+ };
+
+To enable the fprobe, call one of register_fprobe(), register_fprobe_ips(), and
+register_fprobe_syms(). These functions register the fprobe with different types
+of parameters.
+
+The register_fprobe() enables a fprobe by function-name filters.
+E.g. this enables @fp on "func*()" function except "func2()".::
+
+  register_fprobe(&fp, "func*", "func2");
+
+The register_fprobe_ips() enables a fprobe by ftrace-location addresses.
+E.g.
+
+.. code-block:: c
+
+  unsigned long ips[] = { 0x.... };
+
+  register_fprobe_ips(&fp, ips, ARRAY_SIZE(ips));
+
+And the register_fprobe_syms() enables a fprobe by symbol names.
+E.g.
+
+.. code-block:: c
+
+  char syms[] = {"func1", "func2", "func3"};
+
+  register_fprobe_syms(&fp, syms, ARRAY_SIZE(syms));
+
+To disable (remove from functions) this fprobe, call::
+
+  unregister_fprobe(&fp);
+
+You can temporally (soft) disable the fprobe by::
+
+  disable_fprobe(&fp);
+
+and resume by::
+
+  enable_fprobe(&fp);
+
+The above is defined by including the header::
+
+  #include <linux/fprobe.h>
+
+Same as ftrace, the registered callbacks will start being called some time
+after the register_fprobe() is called and before it returns. See
+Documentation/trace/ftrace.rst.
+
+Also, the unregister_fprobe() will guarantee that both enter and exit
+handlers are no longer being called by functions after unregister_fprobe()
+returns as same as unregister_ftrace_function().
+
+The fprobe entry/exit handler
+=============================
+
+The prototype of the entry/exit callback function are as follows:
+
+.. code-block:: c
+
+ int entry_callback(struct fprobe *fp, unsigned long entry_ip, unsigned long ret_ip, struct ftrace_regs *fregs, void *entry_data);
+
+ void exit_callback(struct fprobe *fp, unsigned long entry_ip, unsigned long ret_ip, struct ftrace_regs *fregs, void *entry_data);
+
+Note that the @entry_ip is saved at function entry and passed to exit
+handler.
+If the entry callback function returns !0, the corresponding exit callback
+will be cancelled.
+
+@fp
+        This is the address of `fprobe` data structure related to this handler.
+        You can embed the `fprobe` to your data structure and get it by
+        container_of() macro from @fp. The @fp must not be NULL.
+
+@entry_ip
+        This is the ftrace address of the traced function (both entry and exit).
+        Note that this may not be the actual entry address of the function but
+        the address where the ftrace is instrumented.
+
+@ret_ip
+        This is the return address that the traced function will return to,
+        somewhere in the caller. This can be used at both entry and exit.
+
+@fregs
+        This is the `ftrace_regs` data structure at the entry and exit. This
+        includes the function parameters, or the return values. So user can
+        access those values via appropriate `ftrace_regs_*` APIs.
+
+@entry_data
+        This is a local storage to share the data between entry and exit handlers.
+        This storage is NULL by default. If the user specify `exit_handler` field
+        and `entry_data_size` field when registering the fprobe, the storage is
+        allocated and passed to both `entry_handler` and `exit_handler`.
+
+Entry data size and exit handlers on the same function
+======================================================
+
+Since the entry data is passed via per-task stack and it has limited size,
+the entry data size per probe is limited to `15 * sizeof(long)`. You also need
+to take care that the different fprobes are probing on the same function, this
+limit becomes smaller. The entry data size is aligned to `sizeof(long)` and
+each fprobe which has exit handler uses a `sizeof(long)` space on the stack,
+you should keep the number of fprobes on the same function as small as
+possible.
+
+Share the callbacks with kprobes
+================================
+
+Since the recursion safeness of the fprobe (and ftrace) is a bit different
+from the kprobes, this may cause an issue if user wants to run the same
+code from the fprobe and the kprobes.
+
+Kprobes has per-cpu 'current_kprobe' variable which protects the kprobe
+handler from recursion in all cases. On the other hand, fprobe uses
+only ftrace_test_recursion_trylock(). This allows interrupt context to
+call another (or same) fprobe while the fprobe user handler is running.
+
+This is not a matter if the common callback code has its own recursion
+detection, or it can handle the recursion in the different contexts
+(normal/interrupt/NMI.)
+But if it relies on the 'current_kprobe' recursion lock, it has to check
+kprobe_running() and use kprobe_busy_*() APIs.
+
+Fprobe has FPROBE_FL_KPROBE_SHARED flag to do this. If your common callback
+code will be shared with kprobes, please set FPROBE_FL_KPROBE_SHARED
+*before* registering the fprobe, like:
+
+.. code-block:: c
+
+ fprobe.flags = FPROBE_FL_KPROBE_SHARED;
+
+ register_fprobe(&fprobe, "func*", NULL);
+
+This will protect your common callback from the nested call.
+
+The missed counter
+==================
+
+The `fprobe` data structure has `fprobe::nmissed` counter field as same as
+kprobes.
+This counter counts up when;
+
+ - fprobe fails to take ftrace_recursion lock. This usually means that a function
+   which is traced by other ftrace users is called from the entry_handler.
+
+ - fprobe fails to setup the function exit because of failing to allocate the
+   data buffer from the per-task shadow stack.
+
+The `fprobe::nmissed` field counts up in both cases. Therefore, the former
+skips both of entry and exit callback and the latter skips the exit
+callback, but in both case the counter will increase by 1.
+
+Note that if you set the FTRACE_OPS_FL_RECURSION and/or FTRACE_OPS_FL_RCU to
+`fprobe::ops::flags` (ftrace_ops::flags) when registering the fprobe, this
+counter may not work correctly, because ftrace skips the fprobe function which
+increase the counter.
+
+
+Functions and structures
+========================
+
+.. kernel-doc:: include/linux/fprobe.h
+.. kernel-doc:: kernel/trace/fprobe.c
+