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, 143 insertions, 0 deletions

diff --git a/Documentation/trace/stm.rst b/Documentation/trace/stm.rst
new file mode 100644
index 000000000..1ed49dde0
--- /dev/null
+++ b/Documentation/trace/stm.rst
@@ -0,0 +1,143 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+System Trace Module
+===================
+
+System Trace Module (STM) is a device described in MIPI STP specs as
+STP trace stream generator. STP (System Trace Protocol) is a trace
+protocol multiplexing data from multiple trace sources, each one of
+which is assigned a unique pair of master and channel. While some of
+these masters and channels are statically allocated to certain
+hardware trace sources, others are available to software. Software
+trace sources are usually free to pick for themselves any
+master/channel combination from this pool.
+
+On the receiving end of this STP stream (the decoder side), trace
+sources can only be identified by master/channel combination, so in
+order for the decoder to be able to make sense of the trace that
+involves multiple trace sources, it needs to be able to map those
+master/channel pairs to the trace sources that it understands.
+
+For instance, it is helpful to know that syslog messages come on
+master 7 channel 15, while arbitrary user applications can use masters
+48 to 63 and channels 0 to 127.
+
+To solve this mapping problem, stm class provides a policy management
+mechanism via configfs, that allows defining rules that map string
+identifiers to ranges of masters and channels. If these rules (policy)
+are consistent with what decoder expects, it will be able to properly
+process the trace data.
+
+This policy is a tree structure containing rules (policy_node) that
+have a name (string identifier) and a range of masters and channels
+associated with it, located in "stp-policy" subsystem directory in
+configfs. The topmost directory's name (the policy) is formatted as
+the STM device name to which this policy applies and an arbitrary
+string identifier separated by a stop. From the example above, a rule
+may look like this::
+
+	$ ls /config/stp-policy/dummy_stm.my-policy/user
+	channels masters
+	$ cat /config/stp-policy/dummy_stm.my-policy/user/masters
+	48 63
+	$ cat /config/stp-policy/dummy_stm.my-policy/user/channels
+	0 127
+
+which means that the master allocation pool for this rule consists of
+masters 48 through 63 and channel allocation pool has channels 0
+through 127 in it. Now, any producer (trace source) identifying itself
+with "user" identification string will be allocated a master and
+channel from within these ranges.
+
+These rules can be nested, for example, one can define a rule "dummy"
+under "user" directory from the example above and this new rule will
+be used for trace sources with the id string of "user/dummy".
+
+Trace sources have to open the stm class device's node and write their
+trace data into its file descriptor.
+
+In order to find an appropriate policy node for a given trace source,
+several mechanisms can be used. First, a trace source can explicitly
+identify itself by calling an STP_POLICY_ID_SET ioctl on the character
+device's file descriptor, providing their id string, before they write
+any data there. Secondly, if they chose not to perform the explicit
+identification (because you may not want to patch existing software
+to do this), they can just start writing the data, at which point the
+stm core will try to find a policy node with the name matching the
+task's name (e.g., "syslogd") and if one exists, it will be used.
+Thirdly, if the task name can't be found among the policy nodes, the
+catch-all entry "default" will be used, if it exists. This entry also
+needs to be created and configured by the system administrator or
+whatever tools are taking care of the policy configuration. Finally,
+if all the above steps failed, the write() to an stm file descriptor
+will return a error (EINVAL).
+
+Previously, if no policy nodes were found for a trace source, the stm
+class would silently fall back to allocating the first available
+contiguous range of master/channels from the beginning of the device's
+master/channel range. The new requirement for a policy node to exist
+will help programmers and sysadmins identify gaps in configuration
+and have better control over the un-identified sources.
+
+Some STM devices may allow direct mapping of the channel mmio regions
+to userspace for zero-copy writing. One mappable page (in terms of
+mmu) will usually contain multiple channels' mmios, so the user will
+need to allocate that many channels to themselves (via the
+aforementioned ioctl() call) to be able to do this. That is, if your
+stm device's channel mmio region is 64 bytes and hardware page size is
+4096 bytes, after a successful STP_POLICY_ID_SET ioctl() call with
+width==64, you should be able to mmap() one page on this file
+descriptor and obtain direct access to an mmio region for 64 channels.
+
+Examples of STM devices are Intel(R) Trace Hub [1] and Coresight STM
+[2].
+
+stm_source
+==========
+
+For kernel-based trace sources, there is "stm_source" device
+class. Devices of this class can be connected and disconnected to/from
+stm devices at runtime via a sysfs attribute called "stm_source_link"
+by writing the name of the desired stm device there, for example::
+
+	$ echo dummy_stm.0 > /sys/class/stm_source/console/stm_source_link
+
+For examples on how to use stm_source interface in the kernel, refer
+to stm_console, stm_heartbeat or stm_ftrace drivers.
+
+Each stm_source device will need to assume a master and a range of
+channels, depending on how many channels it requires. These are
+allocated for the device according to the policy configuration. If
+there's a node in the root of the policy directory that matches the
+stm_source device's name (for example, "console"), this node will be
+used to allocate master and channel numbers. If there's no such policy
+node, the stm core will use the catch-all entry "default", if one
+exists. If neither policy nodes exist, the write() to stm_source_link
+will return an error.
+
+stm_console
+===========
+
+One implementation of this interface also used in the example above is
+the "stm_console" driver, which basically provides a one-way console
+for kernel messages over an stm device.
+
+To configure the master/channel pair that will be assigned to this
+console in the STP stream, create a "console" policy entry (see the
+beginning of this text on how to do that). When initialized, it will
+consume one channel.
+
+stm_ftrace
+==========
+
+This is another "stm_source" device, once the stm_ftrace has been
+linked with an stm device, and if "function" tracer is enabled,
+function address and parent function address which Ftrace subsystem
+would store into ring buffer will be exported via the stm device at
+the same time.
+
+Currently only Ftrace "function" tracer is supported.
+
+* [1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf
+* [2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0444b/index.html