riscv: ftrace: do not use stop_machine to update code

Now it is safe to remove dependency from stop_machine() for us to patch
code in ftrace.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20250407180838.42877-6-andybnac@gmail.com
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index ea04f09..b133c60 100644 (file)
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -24,23 +24,13 @@ unsigned long arch_ftrace_get_symaddr(unsigned long fentry_ip)
        return fentry_ip - MCOUNT_AUIPC_SIZE;
 }
 
-void ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
+void arch_ftrace_update_code(int command)
 {
        mutex_lock(&text_mutex);
-
-       /*
-        * The code sequences we use for ftrace can't be patched while the
-        * kernel is running, so we need to use stop_machine() to modify them
-        * for now.  This doesn't play nice with text_mutex, we use this flag
-        * to elide the check.
-        */
-       riscv_patch_in_stop_machine = true;
-}
-
-void ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
-{
-       riscv_patch_in_stop_machine = false;
+       command |= FTRACE_MAY_SLEEP;
+       ftrace_modify_all_code(command);
        mutex_unlock(&text_mutex);
+       flush_icache_all();
 }
 
 static int __ftrace_modify_call(unsigned long source, unsigned long target, bool validate)
@@ -129,51 +119,17 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
         * before the write to function_trace_op later in the generic ftrace.
         * If the sequence is not enforced, then an old ftrace_call_dest may
         * race loading a new function_trace_op set in ftrace_modify_all_code
-        *
-        * If we are in stop_machine, then we don't need to call remote fence
-        * as there is no concurrent read-side of ftrace_call_dest.
         */
        smp_wmb();
-       if (!irqs_disabled())
-               smp_call_function(ftrace_sync_ipi, NULL, 1);
-       return 0;
-}
-
-struct ftrace_modify_param {
-       int command;
-       atomic_t cpu_count;
-};
-
-static int __ftrace_modify_code(void *data)
-{
-       struct ftrace_modify_param *param = data;
-
-       if (atomic_inc_return(&param->cpu_count) == num_online_cpus()) {
-               ftrace_modify_all_code(param->command);
-               /*
-                * Make sure the patching store is effective *before* we
-                * increment the counter which releases all waiting CPUs
-                * by using the release variant of atomic increment. The
-                * release pairs with the call to local_flush_icache_all()
-                * on the waiting CPU.
-                */
-               atomic_inc_return_release(&param->cpu_count);
-       } else {
-               while (atomic_read(&param->cpu_count) <= num_online_cpus())
-                       cpu_relax();
-
-               local_flush_icache_all();
-       }
-
+       /*
+        * Updating ftrace dpes not take stop_machine path, so irqs should not
+        * be disabled.
+        */
+       WARN_ON(irqs_disabled());
+       smp_call_function(ftrace_sync_ipi, NULL, 1);
        return 0;
 }
 
-void arch_ftrace_update_code(int command)
-{
-       struct ftrace_modify_param param = { command, ATOMIC_INIT(0) };
-
-       stop_machine(__ftrace_modify_code, &param, cpu_online_mask);
-}
 #else /* CONFIG_DYNAMIC_FTRACE */
 unsigned long ftrace_call_adjust(unsigned long addr)
 {