uprobes: Do not delete uprobe if uprobe_unregister() fails

delete_uprobe() must not be called if register_for_each_vma(false)
fails to remove all breakpoints, __uprobe_unregister() is correct.
The problem is that register_for_each_vma(false) always returns 0
and thus this logic does not work.

1. Change verify_opcode() to return 0 rather than -EINVAL when
   unregister detects the !is_swbp insn, we can treat this case
   as success and currently unregister paths ignore the error
   code anyway.

2. Change remove_breakpoint() to propagate the error code from
   write_opcode().

3. Change register_for_each_vma(is_register => false) to remove
   as much breakpoints as possible but return non-zero if
   remove_breakpoint() fails at least once.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

kernel/events/uprobes.c

@@ -203,7 +203,7 @@ static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t
 			return 0;
 	} else {
 		if (!is_swbp)		/* unregister: was it changed by us? */
-			return -EINVAL;
+			return 0;
 	}
 
 	return 1;
@@ -616,15 +616,15 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
 	return ret;
 }
 
-static void
+static int
 remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
 {
 	/* can happen if uprobe_register() fails */
 	if (!test_bit(MMF_HAS_UPROBES, &mm->flags))
-		return;
+		return 0;
 
 	set_bit(MMF_RECALC_UPROBES, &mm->flags);
-	set_orig_insn(&uprobe->arch, mm, vaddr);
+	return set_orig_insn(&uprobe->arch, mm, vaddr);
 }
 
 /*
@@ -740,7 +740,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 		struct mm_struct *mm = info->mm;
 		struct vm_area_struct *vma;
 
-		if (err)
+		if (err && is_register)
 			goto free;
 
 		down_write(&mm->mmap_sem);
@@ -756,7 +756,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 		if (is_register)
 			err = install_breakpoint(uprobe, mm, vma, info->vaddr);
 		else
-			remove_breakpoint(uprobe, mm, info->vaddr);
+			err |= remove_breakpoint(uprobe, mm, info->vaddr);
 
  unlock:
 		up_write(&mm->mmap_sem);