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, 18 insertions, 0 deletions

diff --git a/Documentation/networking/failover.rst b/Documentation/networking/failover.rst
new file mode 100644
index 000000000..f0c8483cd
--- /dev/null
+++ b/Documentation/networking/failover.rst
@@ -0,0 +1,18 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========
+FAILOVER
+========
+
+Overview
+========
+
+The failover module provides a generic interface for paravirtual drivers
+to register a netdev and a set of ops with a failover instance. The ops
+are used as event handlers that get called to handle netdev register/
+unregister/link change/name change events on slave pci ethernet devices
+with the same mac address as the failover netdev.
+
+This enables paravirtual drivers to use a VF as an accelerated low latency
+datapath. It also allows live migration of VMs with direct attached VFs by
+failing over to the paravirtual datapath when the VF is unplugged.