ptrace: move clearing of TIF_SYSCALL_EMU flag to core

While the TIF_SYSCALL_EMU is set in ptrace_resume independent of any
architecture, currently only powerpc and x86 unset the TIF_SYSCALL_EMU
flag in ptrace_disable which gets called from ptrace_detach.

Let's move the clearing of TIF_SYSCALL_EMU flag to __ptrace_unlink
which gets executed from ptrace_detach and also keep it along with
or close to clearing of TIF_SYSCALL_TRACE.

Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/powerpc/kernel/ptrace.c

@@ -2521,7 +2521,6 @@ void ptrace_disable(struct task_struct *child)
 {
 	/* make sure the single step bit is not set. */
 	user_disable_single_step(child);
-	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 }
 
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS

arch/x86/kernel/ptrace.c

@@ -747,9 +747,6 @@ static int ioperm_get(struct task_struct *target,
 void ptrace_disable(struct task_struct *child)
 {
 	user_disable_single_step(child);
-#ifdef TIF_SYSCALL_EMU
-	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
-#endif
 }
 
 #if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION

kernel/ptrace.c

@@ -118,6 +118,9 @@ void __ptrace_unlink(struct task_struct *child)
 	BUG_ON(!child->ptrace);
 
 	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+#ifdef TIF_SYSCALL_EMU
+	clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
+#endif
 
 	child->parent = child->real_parent;
 	list_del_init(&child->ptrace_entry);