[PATCH 5/5] ptrace: Revert "Prepare to fix racy accesses on task breakpoints"

[Oleg Nesterov <oleg@redhat.com>]

This reverts commit bf26c018490c2fce7fe9b629083b96ce0e6ad019.

The patch was fine but we can no longer race with SIGKILL after
9899d11f "ptrace: ensure arch_ptrace/ptrace_request can never race
with SIGKILL", the __TASK_TRACED tracee can't be woken up and
->ptrace_bps[] can't go away.

Now that ptrace_get_breakpoints/ptrace_put_breakpoints have no
callers, we can kill them and remove task->ptrace_bp_refcnt.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/ptrace.h |   10 ----------
 include/linux/sched.h  |    3 ---
 kernel/exit.c          |    2 +-
 kernel/ptrace.c        |   16 ----------------
 4 files changed, 1 insertions(+), 30 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 89573a3..07d0df6 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -142,9 +142,6 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
 {
 	INIT_LIST_HEAD(&child->ptrace_entry);
 	INIT_LIST_HEAD(&child->ptraced);
-#ifdef CONFIG_HAVE_HW_BREAKPOINT
-	atomic_set(&child->ptrace_bp_refcnt, 1);
-#endif
 	child->jobctl = 0;
 	child->ptrace = 0;
 	child->parent = child->real_parent;
@@ -351,11 +348,4 @@ extern int task_current_syscall(struct task_struct *target, long *callno,
 				unsigned long args[6], unsigned int maxargs,
 				unsigned long *sp, unsigned long *pc);
 
-#ifdef CONFIG_HAVE_HW_BREAKPOINT
-extern int ptrace_get_breakpoints(struct task_struct *tsk);
-extern void ptrace_put_breakpoints(struct task_struct *tsk);
-#else
-static inline void ptrace_put_breakpoints(struct task_struct *tsk) { }
-#endif /* CONFIG_HAVE_HW_BREAKPOINT */
-
 #endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index d35d2b6..89dc3e4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1570,9 +1570,6 @@ struct task_struct {
 	} memcg_batch;
 	unsigned int memcg_kmem_skip_account;
 #endif
-#ifdef CONFIG_HAVE_HW_BREAKPOINT
-	atomic_t ptrace_bp_refcnt;
-#endif
 #ifdef CONFIG_UPROBES
 	struct uprobe_task *utask;
 #endif
diff --git a/kernel/exit.c b/kernel/exit.c
index 60bc027..0a66f6d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -819,7 +819,7 @@ void do_exit(long code)
 	/*
 	 * FIXME: do that only when needed, using sched_exit tracepoint
 	 */
-	ptrace_put_breakpoints(tsk);
+	flush_ptrace_hw_breakpoint(tsk);
 
 	exit_notify(tsk, group_dead);
 #ifdef CONFIG_NUMA
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index acbd284..776ab3b 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1098,19 +1098,3 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
 	return ret;
 }
 #endif	/* CONFIG_COMPAT */
-
-#ifdef CONFIG_HAVE_HW_BREAKPOINT
-int ptrace_get_breakpoints(struct task_struct *tsk)
-{
-	if (atomic_inc_not_zero(&tsk->ptrace_bp_refcnt))
-		return 0;
-
-	return -1;
-}
-
-void ptrace_put_breakpoints(struct task_struct *tsk)
-{
-	if (atomic_dec_and_test(&tsk->ptrace_bp_refcnt))
-		flush_ptrace_hw_breakpoint(tsk);
-}
-#endif /* CONFIG_HAVE_HW_BREAKPOINT */
-- 
1.5.5.1