[PATCH v2] riscv: ftrace: Properly acquire text_mutex to fix a race condition

[Alexandre Ghiti]

As reported by lockdep, some patching was done without acquiring
text_mutex, so there could be a race when mapping the page to patch
since we use the same fixmap entry.

Reported-by: Han Gao <rabenda.cn at gmail.com>
Reported-by: Vivian Wang <wangruikang at iscas.ac.cn>
Reported-by: Yao Zi <ziyao at disroot.org>
Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
Tested-by: Yao Zi <ziyao at disroot.org>
Tested-by: Han Gao <rabenda.cn at gmail.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>
---
Changes in v2:
- Add __acquires/__releases annotations (Masami)
- Add TB/RB (Masami, Han)
- Link to v1: https://lore.kernel.org/r/20250708-alex-fixes-v1-1-5b008d3f4d0c@rivosinc.com
---
 arch/riscv/kernel/ftrace.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index 4c6c24380cfd9d6c51f0e4340cd674160b83a610..8d18d6727f0fc8fa17d8f651b9e3a00c779cec85 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -14,6 +14,18 @@
 #include <asm/text-patching.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE
+void ftrace_arch_code_modify_prepare(void)
+	__acquires(&text_mutex)
+{
+	mutex_lock(&text_mutex);
+}
+
+void ftrace_arch_code_modify_post_process(void)
+	__releases(&text_mutex)
+{
+	mutex_unlock(&text_mutex);
+}
+
 unsigned long ftrace_call_adjust(unsigned long addr)
 {
 	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_CALL_OPS))
@@ -29,10 +41,8 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
 
 void arch_ftrace_update_code(int command)
 {
-	mutex_lock(&text_mutex);
 	command |= FTRACE_MAY_SLEEP;
 	ftrace_modify_all_code(command);
-	mutex_unlock(&text_mutex);
 	flush_icache_all();
 }
 
@@ -149,6 +159,8 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	unsigned int nops[2], offset;
 	int ret;
 
+	guard(mutex)(&text_mutex);
+
 	ret = ftrace_rec_set_nop_ops(rec);
 	if (ret)
 		return ret;
@@ -157,9 +169,7 @@ int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 	nops[0] = to_auipc_t0(offset);
 	nops[1] = RISCV_INSN_NOP4;
 
-	mutex_lock(&text_mutex);
 	ret = patch_insn_write((void *)pc, nops, 2 * MCOUNT_INSN_SIZE);
-	mutex_unlock(&text_mutex);
 
 	return ret;
 }

---
base-commit: d7b8f8e20813f0179d8ef519541a3527e7661d3a
change-id: 20250708-alex-fixes-1e719b9899f3

Best regards,
-- 
Alexandre Ghiti <alexghiti at rivosinc.com>