[PATCH AUTOSEL 5.4 06/15] RISC-V: Take text_mutex in ftrace_init_nop()

Sasha Levin
2020-09-21T14:41:20Z

From: Palmer Dabbelt <palmerdabbelt@google.com>

[ Upstream commit 66d18dbda8469a944dfec6c49d26d5946efba218 ]

Without this we get lockdep failures. They're spurious failures as SMP isn't
up when ftrace_init_nop() is called. As far as I can tell the easiest fix is
to just take the lock, which also seems like the safest fix.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/riscv/include/asm/ftrace.h | 7 +++++++
arch/riscv/kernel/ftrace.c | 19 +++++++++++++++++++
2 files changed, 26 insertions(+)

diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index c6dcc5291f972..02fbc175142e2 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -63,4 +63,11 @@ do { \
* Let auipc+jalr be the basic *mcount unit*, so we make it 8 bytes here.
*/
#define MCOUNT_INSN_SIZE 8
+
+#ifndef __ASSEMBLY__
+struct dyn_ftrace;
+int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
+#define ftrace_init_nop ftrace_init_nop
+#endif
+
#endif
diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index c40fdcdeb950a..291c579e12457 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -88,6 +88,25 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
return __ftrace_modify_call(rec->ip, addr, false);
}

+
+/*
+ * This is called early on, and isn't wrapped by
+ * ftrace_arch_code_modify_{prepare,post_process}() and therefor doesn't hold
+ * text_mutex, which triggers a lockdep failure. SMP isn't running so we could
+ * just directly poke the text, but it's simpler to just take the lock
+ * ourselves.
+ */
+int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
+{
+ int out;
+
+ ftrace_arch_code_modify_prepare();
+ out = ftrace_make_nop(mod, rec, MCOUNT_ADDR);
+ ftrace_arch_code_modify_post_process();
+
+ return out;
+}
+
int ftrace_update_ftrace_func(ftrace_func_t func)
{
int ret = __ftrace_modify_call((unsigned long)&ftrace_call,
--
2.25.1