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, 56 insertions, 0 deletions

diff --git a/Documentation/block/cmdline-partition.rst b/Documentation/block/cmdline-partition.rst
new file mode 100644
index 000000000..526ba201d
--- /dev/null
+++ b/Documentation/block/cmdline-partition.rst
@@ -0,0 +1,56 @@
+==============================================
+Embedded device command line partition parsing
+==============================================
+
+The "blkdevparts" command line option adds support for reading the
+block device partition table from the kernel command line.
+
+It is typically used for fixed block (eMMC) embedded devices.
+It has no MBR, so saves storage space. Bootloader can be easily accessed
+by absolute address of data on the block device.
+Users can easily change the partition.
+
+The format for the command line is just like mtdparts:
+
+blkdevparts=<blkdev-def>[;<blkdev-def>]
+  <blkdev-def> := <blkdev-id>:<partdef>[,<partdef>]
+    <partdef> := <size>[@<offset>](part-name)
+
+<blkdev-id>
+    block device disk name. Embedded device uses fixed block device.
+    Its disk name is also fixed, such as: mmcblk0, mmcblk1, mmcblk0boot0.
+
+<size>
+    partition size, in bytes, such as: 512, 1m, 1G.
+    size may contain an optional suffix of (upper or lower case):
+
+      K, M, G, T, P, E.
+
+    "-" is used to denote all remaining space.
+
+<offset>
+    partition start address, in bytes.
+    offset may contain an optional suffix of (upper or lower case):
+
+      K, M, G, T, P, E.
+
+(part-name)
+    partition name. Kernel sends uevent with "PARTNAME". Application can
+    create a link to block device partition with the name "PARTNAME".
+    User space application can access partition by partition name.
+
+ro
+    read-only. Flag the partition as read-only.
+
+Example:
+
+    eMMC disk names are "mmcblk0" and "mmcblk0boot0".
+
+  bootargs::
+
+    'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot)ro,-(kernel)'
+
+  dmesg::
+
+    mmcblk0: p1(data0) p2(data1) p3()
+    mmcblk0boot0: p1(boot) p2(kernel)