[SPARC64]: Fix atomicity of TIF update in flush_thread()

Fix atomicity of TIF update in flush_thread() for sparc64

Fixes correctly the race by using *_ti_thread_flag.

Race :

parent process executing :
sys_ptrace()
(lock_kernel())
(ptrace_get_task_struct(pid))
arch_ptrace()
ptrace_detach()
ptrace_disable(child);
clear_singlestep(child);
clear_tsk_thread_flag(child, TIF_SINGLESTEP);
(which clears the TIF_SINGLESTEP flag atomically from a different
process)
(put_task_struct(child))
(unlock_kernel())

And at the same time, in the child process :
sys_execve()
do_execve()
search_binary_handler()
load_elf_binary()
flush_old_exec()
flush_thread()
doing a non-atomic thread flag update

Signed-off-by: Mathieu Desnoyers <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

arch/sparc64/kernel/process.c

···
 	struct thread_info *t = current_thread_info();
 	struct mm_struct *mm;
 
-	if (t->flags & _TIF_ABI_PENDING)
-		t->flags ^= (_TIF_ABI_PENDING | _TIF_32BIT);
+	if (test_ti_thread_flag(t, TIF_ABI_PENDING)) {
+		clear_ti_thread_flag(t, TIF_ABI_PENDING);
+		if (test_ti_thread_flag(t, TIF_32BIT))
+			clear_ti_thread_flag(t, TIF_32BIT);
+		else
+			set_ti_thread_flag(t, TIF_32BIT);
+	}
 
 	mm = t->task->mm;
 	if (mm)