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From: Andy Chiu <andy.chiu@sifive.com>
Date: Thu, 13 Jun 2024 15:11:11 +0800
Subject: [PATCH 6/8] riscv: ftrace: do not use stop_machine to update code
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Message-Id: <20240613-dev-andyc-dyn-ftrace-v4-v1-6-1a538e12c01e@sifive.com>
References: <20240613-dev-andyc-dyn-ftrace-v4-v1-0-1a538e12c01e@sifive.com>
In-Reply-To: <20240613-dev-andyc-dyn-ftrace-v4-v1-0-1a538e12c01e@sifive.com>
To: Paul Walmsley <paul.walmsley@sifive.com>, 
 Palmer Dabbelt <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, 
 Alexandre Ghiti <alexghiti@rivosinc.com>, Zong Li <zong.li@sifive.com>, 
 Steven Rostedt <rostedt@goodmis.org>, 
 Masami Hiramatsu <mhiramat@kernel.org>, Mark Rutland <mark.rutland@arm.com>, 
 Nathan Chancellor <nathan@kernel.org>, 
 Nick Desaulniers <ndesaulniers@google.com>, 
 Bill Wendling <morbo@google.com>, Justin Stitt <justinstitt@google.com>, 
 Puranjay Mohan <puranjay@kernel.org>
Cc: Palmer Dabbelt <palmer@rivosinc.com>, linux-riscv@lists.infradead.org, 
 linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, 
 llvm@lists.linux.dev, Andy Chiu <andy.chiu@sifive.com>

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>
---
 arch/riscv/kernel/ftrace.c | 53 ++++------------------------------------------
 1 file changed, 4 insertions(+), 49 deletions(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index f3b09f2d3ecc..9a421e151b1d 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -13,23 +13,13 @@
 #include <asm/patch.h>
 
 #ifdef CONFIG_DYNAMIC_FTRACE
-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_check_current_call(unsigned long hook_pos,
@@ -158,41 +148,6 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 	return __ftrace_modify_call_site(&ftrace_call_dest, func, true);
 }
 
-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();
-
-	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);
-}
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS

-- 
2.43.0