[PATCH 1/2] ptrace/x86: flush_ptrace_hw_breakpoint() shoule clear the virtual debug registers

[Oleg Nesterov <oleg@redhat.com>]

flush_ptrace_hw_breakpoint() destroys the counters set by ptrace, but
"leaks" ->debugreg6 and ->ptrace_dr7.

The problem is minor, but still it doesn't look right and flush_thread()
did this until 66cb5917. Now that PTRACE_DETACH does flush_ too this makes
even more sense.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/kernel/hw_breakpoint.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 02f0763..f66ff16 100644
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -393,6 +393,9 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 		unregister_hw_breakpoint(t->ptrace_bps[i]);
 		t->ptrace_bps[i] = NULL;
 	}
+
+	t->debugreg6 = 0;
+	t->ptrace_dr7 = 0;
 }
 
 void hw_breakpoint_restore(void)
-- 
1.5.5.1