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From:   "Eric W. Biederman" <ebiederm@xmission.com>
To:     linux-kernel@vger.kernel.org
Cc:     rjw@rjwysocki.net, Oleg Nesterov <oleg@redhat.com>,
        mingo@kernel.org, vincent.guittot@linaro.org,
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        tj@kernel.org, linux-pm@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
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        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-um@lists.infradead.org, Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        linux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, linux-ia64@vger.kernel.org,
        "Eric W. Biederman" <ebiederm@xmission.com>
Date:   Fri, 29 Apr 2022 16:48:33 -0500
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Subject: [PATCH v2 08/12] ptrace: Remove arch_ptrace_attach
Precedence: bulk

The last remaining implementation of arch_ptrace_attach is ia64's
ptrace_attach_sync_user_rbs which was added at the end of 2007 in
commit aa91a2e90044 ("[IA64] Synchronize RBS on PTRACE_ATTACH").

Reading the comments and examining the code ptrace_attach_sync_user_rbs
has the sole purpose of saving registers to the stack when ptrace_attach
changes TASK_STOPPED to TASK_TRACED.  In all other cases arch_ptrace_stop
takes care of the register saving.

In commit d79fdd6d96f4 ("ptrace: Clean transitions between TASK_STOPPED and TRACED")
modified ptrace_attach to wake up the thread and enter ptrace_stop normally even
when the thread starts out stopped.

This makes ptrace_attach_sync_user_rbs completely unnecessary.  So just
remove it.

Cc: linux-ia64@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 arch/ia64/include/asm/ptrace.h |  4 ---
 arch/ia64/kernel/ptrace.c      | 57 ----------------------------------
 kernel/ptrace.c                | 18 -----------
 3 files changed, 79 deletions(-)

diff --git a/arch/ia64/include/asm/ptrace.h b/arch/ia64/include/asm/ptrace.h
index a10a498eede1..402874489890 100644
--- a/arch/ia64/include/asm/ptrace.h
+++ b/arch/ia64/include/asm/ptrace.h
@@ -139,10 +139,6 @@ static inline long regs_return_value(struct pt_regs *regs)
   #define arch_ptrace_stop_needed() \
 	(!test_thread_flag(TIF_RESTORE_RSE))
 
-  extern void ptrace_attach_sync_user_rbs (struct task_struct *);
-  #define arch_ptrace_attach(child) \
-	ptrace_attach_sync_user_rbs(child)
-
   #define arch_has_single_step()  (1)
   #define arch_has_block_step()   (1)
 
diff --git a/arch/ia64/kernel/ptrace.c b/arch/ia64/kernel/ptrace.c
index a19acd9f5e1f..a45f529046c3 100644
--- a/arch/ia64/kernel/ptrace.c
+++ b/arch/ia64/kernel/ptrace.c
@@ -617,63 +617,6 @@ void ia64_sync_krbs(void)
 	unw_init_running(do_sync_rbs, ia64_sync_kernel_rbs);
 }
 
-/*
- * After PTRACE_ATTACH, a thread's register backing store area in user
- * space is assumed to contain correct data whenever the thread is
- * stopped.  arch_ptrace_stop takes care of this on tracing stops.
- * But if the child was already stopped for job control when we attach
- * to it, then it might not ever get into ptrace_stop by the time we
- * want to examine the user memory containing the RBS.
- */
-void
-ptrace_attach_sync_user_rbs (struct task_struct *child)
-{
-	int stopped = 0;
-	struct unw_frame_info info;
-
-	/*
-	 * If the child is in TASK_STOPPED, we need to change that to
-	 * TASK_TRACED momentarily while we operate on it.  This ensures
-	 * that the child won't be woken up and return to user mode while
-	 * we are doing the sync.  (It can only be woken up for SIGKILL.)
-	 */
-
-	read_lock(&tasklist_lock);
-	if (child->sighand) {
-		spin_lock_irq(&child->sighand->siglock);
-		if (READ_ONCE(child->__state) == TASK_STOPPED &&
-		    !test_and_set_tsk_thread_flag(child, TIF_RESTORE_RSE)) {
-			set_notify_resume(child);
-
-			WRITE_ONCE(child->__state, TASK_TRACED);
-			stopped = 1;
-		}
-		spin_unlock_irq(&child->sighand->siglock);
-	}
-	read_unlock(&tasklist_lock);
-
-	if (!stopped)
-		return;
-
-	unw_init_from_blocked_task(&info, child);
-	do_sync_rbs(&info, ia64_sync_user_rbs);
-
-	/*
-	 * Now move the child back into TASK_STOPPED if it should be in a
-	 * job control stop, so that SIGCONT can be used to wake it up.
-	 */
-	read_lock(&tasklist_lock);
-	if (child->sighand) {
-		spin_lock_irq(&child->sighand->siglock);
-		if (READ_ONCE(child->__state) == TASK_TRACED &&
-		    (child->signal->flags & SIGNAL_STOP_STOPPED)) {
-			WRITE_ONCE(child->__state, TASK_STOPPED);
-		}
-		spin_unlock_irq(&child->sighand->siglock);
-	}
-	read_unlock(&tasklist_lock);
-}
-
 /*
  * Write f32-f127 back to task->thread.fph if it has been modified.
  */
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 644eb7439d01..22041531adf6 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -1280,10 +1280,6 @@ int ptrace_request(struct task_struct *child, long request,
 	return ret;
 }
 
-#ifndef arch_ptrace_attach
-#define arch_ptrace_attach(child)	do { } while (0)
-#endif
-
 SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 		unsigned long, data)
 {
@@ -1292,8 +1288,6 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 
 	if (request == PTRACE_TRACEME) {
 		ret = ptrace_traceme();
-		if (!ret)
-			arch_ptrace_attach(current);
 		goto out;
 	}
 
@@ -1305,12 +1299,6 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 
 	if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
 		ret = ptrace_attach(child, request, addr, data);
-		/*
-		 * Some architectures need to do book-keeping after
-		 * a ptrace attach.
-		 */
-		if (!ret)
-			arch_ptrace_attach(child);
 		goto out_put_task_struct;
 	}
 
@@ -1450,12 +1438,6 @@ COMPAT_SYSCALL_DEFINE4(ptrace, compat_long_t, request, compat_long_t, pid,
 
 	if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) {
 		ret = ptrace_attach(child, request, addr, data);
-		/*
-		 * Some architectures need to do book-keeping after
-		 * a ptrace attach.
-		 */
-		if (!ret)
-			arch_ptrace_attach(child);
 		goto out_put_task_struct;
 	}
 
-- 
2.35.3