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, 74 insertions, 0 deletions

diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
new file mode 100644
index 000000000..01a37ec87
--- /dev/null
+++ b/scripts/Makefile.modfinal
@@ -0,0 +1,74 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# ===========================================================================
+# Module final link
+# ===========================================================================
+
+PHONY := __modfinal
+__modfinal:
+
+include $(objtree)/include/config/auto.conf
+include $(srctree)/scripts/Kbuild.include
+include $(srctree)/scripts/Makefile.lib
+
+# find all modules listed in modules.order
+modules := $(call read-file, modules.order)
+
+__modfinal: $(modules:%.o=%.ko)
+	@:
+
+# modname and part-of-module are set to make c_flags define proper module flags
+modname = $(notdir $(@:.mod.o=))
+part-of-module = y
+GCOV_PROFILE := n
+ccflags-remove-y := $(CC_FLAGS_CFI)
+
+%.mod.o: %.mod.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+.module-common.o: $(srctree)/scripts/module-common.c FORCE
+	$(call if_changed_rule,cc_o_c)
+
+ifneq ($(WARN_ON_UNUSED_TRACEPOINTS),)
+cmd_check_tracepoint = $(objtree)/scripts/tracepoint-update --module $<;
+endif
+
+quiet_cmd_ld_ko_o = LD [M]  $@
+      cmd_ld_ko_o =							\
+	$(LD) -r $(KBUILD_LDFLAGS)					\
+		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\
+		-T $(objtree)/scripts/module.lds -o $@ $(filter %.o, $^)
+
+quiet_cmd_btf_ko = BTF [M] $@
+      cmd_btf_ko = 							\
+	if [ ! -f $(objtree)/vmlinux ]; then				\
+		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
+	else	\
+		$(CONFIG_SHELL) $(srctree)/scripts/gen-btf.sh --btf_base $(objtree)/vmlinux $@; \
+	fi;
+
+# Re-generate module BTFs if either module's .ko or vmlinux changed
+%.ko: %.o %.mod.o .module-common.o $(objtree)/scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),$(objtree)/vmlinux) FORCE
+	+$(call if_changed,ld_ko_o)
+ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+	+$(if $(newer-prereqs),$(call cmd,btf_ko))
+endif
+	+$(call cmd,check_tracepoint)
+
+targets += $(modules:%.o=%.ko) $(modules:%.o=%.mod.o) .module-common.o
+
+# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
+# ---------------------------------------------------------------------------
+
+PHONY += FORCE
+FORCE:
+
+# Read all saved command lines and dependencies for the $(targets) we
+# may be building above, using $(if_changed{,_dep}). As an
+# optimization, we don't need to read them if the target does not
+# exist, we will rebuild anyway in that case.
+
+existing-targets := $(wildcard $(sort $(targets)))
+
+-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
+
+.PHONY: $(PHONY)