As the generic entry, before report_syscall_exit(), it terminate
the process if the syscall is issued within a restartable sequence.

In preparation for moving arm64 over to the generic entry code,
refator el0_svc_common() as below:

- Extract syscall_exit_to_user_mode_prepare() helper to replace the
  the combination of read_thread_flags() and syscall_trace_exit(), also
  move the syscall exit check logic into it.

- Move rseq_syscall() ahead, so the CONFIG_DEBUG_RSEQ check is
  not needed.

- Move has_syscall_work() helper into asm/syscall.h to be reused for
  ptrace.c.

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
---
 arch/arm64/include/asm/syscall.h |  7 ++++++-
 arch/arm64/kernel/ptrace.c       | 10 +++++++++-
 arch/arm64/kernel/syscall.c      | 26 +++++---------------------
 3 files changed, 20 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index 925a257145f9..6eeb1e7b033f 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -85,7 +85,12 @@ static inline int syscall_get_arch(struct task_struct *task)
 	return AUDIT_ARCH_AARCH64;
 }
 
+static inline bool has_syscall_work(unsigned long flags)
+{
+	return unlikely(flags & _TIF_SYSCALL_WORK);
+}
+
 int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags);
-void syscall_trace_exit(struct pt_regs *regs, unsigned long flags);
+void syscall_exit_to_user_mode_prepare(struct pt_regs *regs);
 
 #endif	/* __ASM_SYSCALL_H */
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index bb994d668d74..23df2e558fe9 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -2384,7 +2384,7 @@ int syscall_trace_enter(struct pt_regs *regs, long syscall, unsigned long flags)
 	return regs->syscallno;
 }
 
-void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
+static void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
 {
 	audit_syscall_exit(regs);
 
@@ -2393,8 +2393,16 @@ void syscall_trace_exit(struct pt_regs *regs, unsigned long flags)
 
 	if (flags & (_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP))
 		report_syscall_exit(regs);
+}
+
+void syscall_exit_to_user_mode_prepare(struct pt_regs *regs)
+{
+	unsigned long flags = read_thread_flags();
 
 	rseq_syscall(regs);
+
+	if (has_syscall_work(flags) || flags & _TIF_SINGLESTEP)
+		syscall_trace_exit(regs, flags);
 }
 
 /*
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index 064dc114fb9b..a50db885fc34 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -65,11 +65,6 @@ static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
 	choose_random_kstack_offset(get_random_u16());
 }
 
-static inline bool has_syscall_work(unsigned long flags)
-{
-	return unlikely(flags & _TIF_SYSCALL_WORK);
-}
-
 static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 			   const syscall_fn_t syscall_table[])
 {
@@ -125,26 +120,15 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
 		if (scno == NO_SYSCALL)
 			syscall_set_return_value(current, regs, -ENOSYS, 0);
 		scno = syscall_trace_enter(regs, regs->syscallno, flags);
-		if (scno == NO_SYSCALL)
-			goto trace_exit;
+		if (scno == NO_SYSCALL) {
+			syscall_exit_to_user_mode_prepare(regs);
+			return;
+		}
 	}
 
 	invoke_syscall(regs, scno, sc_nr, syscall_table);
 
-	/*
-	 * The tracing status may have changed under our feet, so we have to
-	 * check again. However, if we were tracing entry, then we always trace
-	 * exit regardless, as the old entry assembly did.
-	 */
-	if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
-		flags = read_thread_flags();
-		if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
-			return;
-	}
-
-trace_exit:
-	flags = read_thread_flags();
-	syscall_trace_exit(regs, flags);
+	syscall_exit_to_user_mode_prepare(regs);
 }
 
 void do_el0_svc(struct pt_regs *regs)
-- 
2.34.1