+ /*
+ * There's a problem with moving the arch_install_thread_hw_breakpoint()
+ * call before current is updated. Suppose a kernel breakpoint is
+ * triggered in between the two, the hw-breakpoint handler will see that
+ * the 'current' task does not have TIF_DEBUG flag set and will think it
+ * is leftover from an old task (lazy switching) and will erase it. Then
+ * until the next context switch, no user-breakpoints will be installed.
+ *
+ * The real problem is that it's impossible to update both current and
+ * physical debug registers at the same instant, so there will always be
+ * a window in which they disagree and a breakpoint might get triggered.
+ * Since we use lazy switching, we are forced to assume that a
+ * disagreement means that current is correct and the exception is due
+ * to lazy debug register switching.
+ */
+ if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG)))
+ arch_install_thread_hw_breakpoint(next_p);