[PATCH 3/3] riscv: Use text_mutex instead of patch_lock

From: Zong Li
Date: Tue Apr 21 2020 - 03:30:22 EST


We don't need the additional lock protection when patching the text.

There are two patching interfaces here:
- patch_text: patch code and always synchronize with stop_machine()
- patch_text_nosync: patch code without synchronization, it's caller's
responsibility to synchronize all CPUs if needed.

For the first one, stop_machine() is protected by its own mutex, and
also the irq is already disabled here.

For the second one, in risc-v real case now, it would be used to ftrace
patching the mcount function, since it already running under
kstop_machine(), no other thread will run, so we could use text_mutex
on ftrace side.

Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
Reviewed-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
---
arch/riscv/kernel/ftrace.c | 13 +++++++++++++
arch/riscv/kernel/patch.c | 13 +++++++------
2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
index fb1e2b8fe254..08396614d6f4 100644
--- a/arch/riscv/kernel/ftrace.c
+++ b/arch/riscv/kernel/ftrace.c
@@ -7,10 +7,23 @@

#include <linux/ftrace.h>
#include <linux/uaccess.h>
+#include <linux/memory.h>
#include <asm/cacheflush.h>
#include <asm/patch.h>

#ifdef CONFIG_DYNAMIC_FTRACE
+int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex)
+{
+ mutex_lock(&text_mutex);
+ return 0;
+}
+
+int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex)
+{
+ mutex_unlock(&text_mutex);
+ return 0;
+}
+
static int ftrace_check_current_call(unsigned long hook_pos,
unsigned int *expected)
{
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 8acb9ae2da08..5805791cd5b5 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -5,6 +5,7 @@

#include <linux/spinlock.h>
#include <linux/mm.h>
+#include <linux/memory.h>
#include <linux/uaccess.h>
#include <linux/stop_machine.h>
#include <asm/kprobes.h>
@@ -18,8 +19,6 @@ struct patch_insn {
};

#ifdef CONFIG_MMU
-static DEFINE_RAW_SPINLOCK(patch_lock);
-
static void *patch_map(void *addr, int fixmap)
{
uintptr_t uintaddr = (uintptr_t) addr;
@@ -49,10 +48,14 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
{
void *waddr = addr;
bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
- unsigned long flags = 0;
int ret;

- raw_spin_lock_irqsave(&patch_lock, flags);
+ /*
+ * Before reaching here, it was expected to lock the text_mutex
+ * already, so we don't need to give another lock here and could
+ * ensure that it was safe between each cores.
+ */
+ lockdep_assert_held(&text_mutex);

if (across_pages)
patch_map(addr + len, FIX_TEXT_POKE1);
@@ -66,8 +69,6 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
if (across_pages)
patch_unmap(FIX_TEXT_POKE1);

- raw_spin_unlock_irqrestore(&patch_lock, flags);
-
return ret;
}
NOKPROBE_SYMBOL(patch_insn_write);
--
2.26.1