Fix atomicity of TIF update in flush_thread() for sparc64

Fix atomicity of TIF update in flush_thread() for x86_64

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

It applies on 2.6.20.

@@ -413,8 +413,13 @@ void flush_thread(void)
 	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_tsk_thread_flag(tsk, TIF_ABI_PENDING)) {
+		clear_tsk_thread_flag(tsk, TIF_ABI_PENDING);
+		if (test_tsk_thread_flag(tsk, TIF_32BIT))
+			clear_tsk_thread_flag(tsk, TIF_32BIT);
+		else
+			set_tsk_thread_flag(tsk, TIF_32BIT);
+	}
 
 	mm = t->task->mm;
 	if (mm)

Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

From: Mathieu Desnoyers <[email protected]>
Date: Thu, 8 Mar 2007 21:38:14 -0500

                                                    ^^^^^^

You mean sparc64 of course, I fixed this up while committing your patch, thanks a lot.