linux-kernel - [PATCH AUTOSEL 4.19 4/9] RISC-V: Take text_mutex in ftrace_init

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Message-Id: <20200921144114.2135773-4-sashal@kernel.org>
Date:   Mon, 21 Sep 2020 10:41:09 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Guo Ren <guoren@...nel.org>, Sasha Levin <sashal@...nel.org>,
        linux-riscv@...ts.infradead.org
Subject: [PATCH AUTOSEL 4.19 4/9] RISC-V: Take text_mutex in ftrace_init_nop()

From: Palmer Dabbelt <palmerdabbelt@...gle.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@...gle.com>
Acked-by: Guo Ren <guoren@...nel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
Signed-off-by: Sasha Levin <sashal@...nel.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 6d39f64e4dce4..fa8530f05ed4f 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