Unverified Commit 5aa4ef95 authored by Andy Chiu's avatar Andy Chiu Committed by Palmer Dabbelt
Browse files

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: default avatarAndy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20250407180838.42877-6-andybnac@gmail.com


Signed-off-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: default avatarPalmer Dabbelt <palmer@dabbelt.com>
parent b2137c3b

arch/riscv/kernel/ftrace.c

+10 −54
Original line number Diff line number Diff line
@@ -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.

	 * Updating ftrace dpes not take stop_machine path, so irqs should not

	 * be disabled.

	 */

		atomic_inc_return_release(&param->cpu_count);

	} else {

		while (atomic_read(&param->cpu_count) <= num_online_cpus())

			cpu_relax();



		local_flush_icache_all();

	}



	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)

{