ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 224 insertions, 0 deletions

diff --git a/Documentation/devicetree/of_unittest.rst b/Documentation/devicetree/of_unittest.rst
new file mode 100644
index 000000000..6ed6e3291
--- /dev/null
+++ b/Documentation/devicetree/of_unittest.rst
@@ -0,0 +1,224 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+Open Firmware Devicetree Unittest
+=================================
+
+Author: Gaurav Minocha <gaurav.minocha.os@gmail.com>
+
+1. Introduction
+===============
+
+This document explains how the test data required for executing OF unittest
+is attached to the live tree dynamically, independent of the machine's
+architecture.
+
+It is recommended to read the following documents before moving ahead.
+
+(1) Documentation/devicetree/usage-model.rst
+(2) http://www.devicetree.org/Device_Tree_Usage
+
+OF Selftest has been designed to test the interface (include/linux/of.h)
+provided to device driver developers to fetch the device information..etc.
+from the unflattened device tree data structure. This interface is used by
+most of the device drivers in various use cases.
+
+
+2. Verbose Output (EXPECT)
+==========================
+
+If unittest detects a problem it will print a warning or error message to
+the console.  Unittest also triggers warning and error messages from other
+kernel code as a result of intentionally bad unittest data.  This has led
+to confusion as to whether the triggered messages are an expected result
+of a test or whether there is a real problem that is independent of unittest.
+
+'EXPECT \ : text' (begin) and 'EXPECT / : text' (end) messages have been
+added to unittest to report that a warning or error is expected.  The
+begin is printed before triggering the warning or error, and the end is
+printed after triggering the warning or error.
+
+The EXPECT messages result in very noisy console messages that are difficult
+to read.  The script scripts/dtc/of_unittest_expect was created to filter
+this verbosity and highlight mismatches between triggered warnings and
+errors vs expected warnings and errors.  More information is available
+from 'scripts/dtc/of_unittest_expect --help'.
+
+
+3. Test-data
+============
+
+The Device Tree Source file (drivers/of/unittest-data/testcases.dtso) contains
+the test data required for executing the unit tests automated in
+drivers/of/unittest.c. See the content of the folder::
+
+    drivers/of/unittest-data/tests-*.dtsi
+
+for the Device Tree Source Include files (.dtsi) included in testcases.dtso.
+
+When the kernel is built with CONFIG_OF_UNITTEST enabled, then the following make
+rule::
+
+    $(obj)/%.dtbo: $(src)/%.dtso $(DTC) FORCE
+	    $(call if_changed_dep,dtc)
+
+is used to compile the DT source file (testcases.dtso) into a binary blob
+(testcases.dtbo), also referred as flattened DT.
+
+After that, using the following rule the binary blob above is wrapped as an
+assembly file (testcases.dtbo.S)::
+
+    $(obj)/%.dtbo.S: $(obj)/%.dtbo FORCE
+	    $(call if_changed,wrap_S_dtb)
+
+The assembly file is compiled into an object file (testcases.dtbo.o), and is
+linked into the kernel image.
+
+
+3.1. Adding the test data
+-------------------------
+
+Un-flattened device tree structure:
+
+Un-flattened device tree consists of connected device_node(s) in form of a tree
+structure described below::
+
+    // following struct members are used to construct the tree
+    struct device_node {
+	...
+	struct  device_node *parent;
+	struct  device_node *child;
+	struct  device_node *sibling;
+	...
+    };
+
+Figure 1, describes a generic structure of machine's un-flattened device tree
+considering only child and sibling pointers. There exists another pointer,
+``*parent``, that is used to traverse the tree in the reverse direction. So, at
+a particular level the child node and all the sibling nodes will have a parent
+pointer pointing to a common node (e.g. child1, sibling2, sibling3, sibling4's
+parent points to root node)::
+
+    root ('/')
+    |
+    child1 -> sibling2 -> sibling3 -> sibling4 -> null
+    |         |           |           |
+    |         |           |          null
+    |         |           |
+    |         |        child31 -> sibling32 -> null
+    |         |           |          |
+    |         |          null       null
+    |         |
+    |      child21 -> sibling22 -> sibling23 -> null
+    |         |          |            |
+    |        null       null         null
+    |
+    child11 -> sibling12 -> sibling13 -> sibling14 -> null
+    |           |           |            |
+    |           |           |           null
+    |           |           |
+    null        null       child131 -> null
+			    |
+			    null
+
+Figure 1: Generic structure of un-flattened device tree
+
+
+Before executing OF unittest, it is required to attach the test data to
+machine's device tree (if present). So, when selftest_data_add() is called,
+at first it reads the flattened device tree data linked into the kernel image
+via the following kernel symbols::
+
+    __dtb_testcases_begin - address marking the start of test data blob
+    __dtb_testcases_end   - address marking the end of test data blob
+
+Secondly, it calls of_fdt_unflatten_tree() to unflatten the flattened
+blob. And finally, if the machine's device tree (i.e. live tree) is present,
+then it attaches the unflattened test data tree to the live tree, else it
+attaches itself as a live device tree.
+
+attach_node_and_children() uses of_attach_node() to attach the nodes into the
+live tree as explained below. To explain the same, the test data tree described
+in Figure 2 is attached to the live tree described in Figure 1::
+
+    root ('/')
+	|
+    testcase-data
+	|
+    test-child0 -> test-sibling1 -> test-sibling2 -> test-sibling3 -> null
+	|               |                |                |
+    test-child01      null             null             null
+
+
+Figure 2: Example test data tree to be attached to live tree.
+
+According to the scenario above, the live tree is already present so it isn't
+required to attach the root('/') node. All other nodes are attached by calling
+of_attach_node() on each node.
+
+In the function of_attach_node(), the new node is attached as the child of the
+given parent in live tree. But, if parent already has a child then the new node
+replaces the current child and turns it into its sibling. So, when the testcase
+data node is attached to the live tree above (Figure 1), the final structure is
+as shown in Figure 3::
+
+    root ('/')
+    |
+    testcase-data -> child1 -> sibling2 -> sibling3 -> sibling4 -> null
+    |               |          |           |           |
+    (...)             |          |           |          null
+		    |          |         child31 -> sibling32 -> null
+		    |          |           |           |
+		    |          |          null        null
+		    |          |
+		    |        child21 -> sibling22 -> sibling23 -> null
+		    |          |           |            |
+		    |         null        null         null
+		    |
+		    child11 -> sibling12 -> sibling13 -> sibling14 -> null
+		    |          |            |            |
+		    null       null          |           null
+					    |
+					    child131 -> null
+					    |
+					    null
+    -----------------------------------------------------------------------
+
+    root ('/')
+    |
+    testcase-data -> child1 -> sibling2 -> sibling3 -> sibling4 -> null
+    |               |          |           |           |
+    |             (...)      (...)       (...)        null
+    |
+    test-sibling3 -> test-sibling2 -> test-sibling1 -> test-child0 -> null
+    |                |                   |                |
+    null             null                null         test-child01
+
+
+Figure 3: Live device tree structure after attaching the testcase-data.
+
+
+Astute readers would have noticed that test-child0 node becomes the last
+sibling compared to the earlier structure (Figure 2). After attaching first
+test-child0 the test-sibling1 is attached that pushes the child node
+(i.e. test-child0) to become a sibling and makes itself a child node,
+as mentioned above.
+
+If a duplicate node is found (i.e. if a node with same full_name property is
+already present in the live tree), then the node isn't attached rather its
+properties are updated to the live tree's node by calling the function
+update_node_properties().
+
+
+3.2. Removing the test data
+---------------------------
+
+Once the test case execution is complete, selftest_data_remove is called in
+order to remove the device nodes attached initially (first the leaf nodes are
+detached and then moving up the parent nodes are removed, and eventually the
+whole tree). selftest_data_remove() calls detach_node_and_children() that uses
+of_detach_node() to detach the nodes from the live device tree.
+
+To detach a node, of_detach_node() either updates the child pointer of given
+node's parent to its sibling or attaches the previous sibling to the given
+node's sibling, as appropriate. That is it :)