hw-breakpoints: Keep track of user disabled breakpoints

When we disable a breakpoint through dr7, we unregister it right
away, making us lose track of its corresponding address
register value.

It means that the following sequence would be unsupported:

 - set address in dr0
 - enable it through dr7
 - disable it through dr7
 - enable it through dr7

because we lost the address register value when we disabled the
breakpoint.

Don't unregister the disabled breakpoints but rather disable
them.

Reported-by: "K.Prasad" <prasad@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1259735536-9236-1-git-send-regression-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 4 deletions

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 2941b32ea666..04d182a7cfdb 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -595,7 +595,7 @@ static unsigned long ptrace_get_dr7(struct perf_event *bp[])
 
 static struct perf_event *
 ptrace_modify_breakpoint(struct perf_event *bp, int len, int type,
-                         struct task_struct *tsk)
+                         struct task_struct *tsk, int disabled)
 {
         int err;
         int gen_len, gen_type;
@@ -616,7 +616,7 @@ ptrace_modify_breakpoint(struct perf_event *bp, int len, int type,
         attr = bp->attr;
         attr.bp_len = gen_len;
         attr.bp_type = gen_type;
-        attr.disabled = 0;
+        attr.disabled = disabled;
 
         return modify_user_hw_breakpoint(bp, &attr, bp->callback, tsk);
 }
@@ -655,13 +655,21 @@ restore:
                                  */
                                 if (!second_pass)
                                         continue;
+
                                 thread->ptrace_bps[i] = NULL;
-                                unregister_hw_breakpoint(bp);
+                                bp = ptrace_modify_breakpoint(bp, len, type,
+                                                              tsk, 1);
+                                if (IS_ERR(bp)) {
+                                        rc = PTR_ERR(bp);
+                                        thread->ptrace_bps[i] = NULL;
+                                        break;
+                                }
+                                thread->ptrace_bps[i] = bp;
                         }
                         continue;
                 }
 
-                bp = ptrace_modify_breakpoint(bp, len, type, tsk);
+                bp = ptrace_modify_breakpoint(bp, len, type, tsk, 0);
 
                 /* Incorrect bp, or we have a bug in bp API */
                 if (IS_ERR(bp)) {