riscv: ftrace: Properly acquire text_mutex to fix a race condition

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@gmail.com>
Reported-by: Vivian Wang <wangruikang@iscas.ac.cn>
Reported-by: Yao Zi <ziyao@disroot.org>
Closes: https://lore.kernel.org/linux-riscv/aGODMpq7TGINddzM@pie.lan/
Tested-by: Yao Zi <ziyao@disroot.org>
Tested-by: Han Gao <rabenda.cn@gmail.com>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20250711-alex-fixes-v2-1-d85a5438da6c@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

Author: Alexandre Ghiti

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;
 }