ptrace: revert "Prepare to fix racy accesses on task breakpoints"

This reverts commit bf26c018490c ("Prepare to fix racy accesses on task
breakpoints").

The patch was fine but we can no longer race with SIGKILL after commit
9899d11f6544 ("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>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Michael Neuling <mikey@neuling.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 1 insertions, 30 deletions

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index 89573a33ab3c..07d0df6bf768 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 cdd5407b37e2..75324d8157e3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1401,9 +1401,6 @@ 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 fafe75d9e6f6..a949819055d5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -808,7 +808,7 @@ 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 ba5e6cea181a..a146ee327f6a 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1221,19 +1221,3 @@ 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 */