[PATCH] ARM64: Clear out any singlestep state on a ptrace detach operation

[John Blackwood <john.blackwood@ccur.com>]

Hello Will,

I have a patch for a ptrace(2) issue that we encountered on arm64 kernels.
If a debugger singlesteps a ptraced task, and then does a ptrace(2)
PTRACE_DETACH command, the task will not resume successfully. It seems
that clearing out the singlestep state, as something like a ptrace(2)
PTRACE_CONT does, gets this working.

Thank you for your time and considerations.

----- -----

arm64: Clear out any singlestep state on a ptrace detach operation.

Make sure to clear out any ptrace singlestep state when a
ptrace(2) PTRACE_DETACH call is made on arm64 systems.

Otherwise, the previously ptraced task will die off with a SIGTRAP signal
if the debugger just previously singlestepped the ptraced task.

Signed-off-by: John Blackwood <john.blackwood@ccur.com>

Index: b/arch/arm64/kernel/ptrace.c
===================================================================
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -58,6 +58,7 @@
   */
  void ptrace_disable(struct task_struct *child)
  {
+	user_disable_single_step(child);
  }
  
  #ifdef CONFIG_HAVE_HW_BREAKPOINT