Subject: Re: bug#23808: Emacs 25 open-network-stream, make-network-process

From: Lars Ingebrigtsen <[email-masked]>
Date: Thu, 11 Aug 2016 12:41:22 +0200

Paul Eggert <[email-masked]> writes:

> [CC'ing this to Lars, since this bug seems to have been introduced by
> the async DNS changes in February.]
>
> Attached is a proposed patch for Bug#23808. The patch attempts to fix
> the bug reported by my anonymous correspondent, who writes "It appears
> that before the refactoring, make-network-process would not create a
> process object if the socket connection failed, or if it had been
> interrupted by ^G. However after the new refactoring, the process
> object is created upfront with status 'run', before the connection is
> attempted. The refactoring failed to preserve the semantics."
>
> From a21dfe515552c7d7f486950e9231b8ca2668f6cc Mon Sep 17 00:00:00 2001
> From: Paul Eggert <[email-masked]>
> Date: Thu, 11 Aug 2016 01:56:16 -0700
> Subject: [PATCH] Fix process leak with make-network-process
>
> This problem was introduced by the recent async changes (Bug#23808).
> * src/process.c (Fmake_process): Move USE_SAFE_ALLOCA later,
> so that it follows the start_process_unwind unwind-protect.
> Set pid to -1 while the process is being created.
> (start_process_unwind): Omit unnecessary emacs_abort test.
> (connect_network_socket): Simplify use of counts.  Unwind
> bind_polling_period a bit earlier, so that a remove_process
> unwind-protect can be added when needed; this is the heart of
> the fix.  Undo the unwind-protect just before returning.
> ---
>  src/process.c | 49 ++++++++++++++++++-------------------------------
>  src/process.h |  9 +++++----
>  2 files changed, 23 insertions(+), 35 deletions(-)
>
> diff --git a/src/process.c b/src/process.c
> index fb32698..69d1b2a 100644
> --- a/src/process.c
> +++ b/src/process.c
> @@ -238,6 +238,7 @@ static int process_output_delay_count;
>  
>  static bool process_output_skip;
>  
> +static void start_process_unwind (Lisp_Object);
>  static void create_process (Lisp_Object, char **, Lisp_Object);
>  #ifdef USABLE_SIGIO
>  static bool keyboard_bit_set (fd_set *);
> @@ -245,11 +246,8 @@ static bool keyboard_bit_set (fd_set *);
>  static void deactivate_process (Lisp_Object);
>  static int status_notify (struct Lisp_Process *, struct Lisp_Process *);
>  static int read_process_output (Lisp_Object, int);
> -static void handle_child_signal (int);
>  static void create_pty (Lisp_Object);
> -
> -static Lisp_Object get_process (register Lisp_Object name);
> -static void exec_sentinel (Lisp_Object proc, Lisp_Object reason);
> +static void exec_sentinel (Lisp_Object, Lisp_Object);
>  
>  /* Mask of bits indicating the descriptors that we wait for input on.  */
>  
> @@ -1407,8 +1405,6 @@ DEFUN ("process-list", Fprocess_list, Sprocess_list, 0, 0, 0,
>  
>  /* Starting asynchronous inferior processes.  */
>  
> -static void start_process_unwind (Lisp_Object proc);
> -
>  DEFUN ("make-process", Fmake_process, Smake_process, 0, MANY, 0,
>         doc: /* Start a program in a subprocess.  Return the process object for it.
>  
> @@ -1459,7 +1455,6 @@ usage: (make-process &rest ARGS)  */)
>    Lisp_Object buffer, name, command, program, proc, contact, current_dir, tem;
>    Lisp_Object xstderr, stderrproc;
>    ptrdiff_t count = SPECPDL_INDEX ();
> -  USE_SAFE_ALLOCA;
>  
>    if (nargs == 0)
>      return Qnil;
> @@ -1508,10 +1503,6 @@ usage: (make-process &rest ARGS)  */)
>      }
>  
>    proc = make_process (name);
> -  /* If an error occurs and we can't start the process, we want to
> -     remove it from the process list.  This means that each error
> -     check in create_process doesn't need to call remove_process
> -     itself; it's all taken care of here.  */
>    record_unwind_protect (start_process_unwind, proc);
>  
>    pset_childp (XPROCESS (proc), Qt);
> @@ -1561,6 +1552,8 @@ usage: (make-process &rest ARGS)  */)
>  		     BUF_ZV (XBUFFER (buffer)),
>  		     BUF_ZV_BYTE (XBUFFER (buffer)));
>  
> +  USE_SAFE_ALLOCA;
> +
>    {
>      /* Decide coding systems for communicating with the process.  Here
>         we don't setup the structure coding_system nor pay attention to
> @@ -1719,18 +1712,11 @@ usage: (make-process &rest ARGS)  */)
>    return unbind_to (count, proc);
>  }
>  
> -/* This function is the unwind_protect form for Fstart_process.  If
> -   PROC doesn't have its pid set, then we know someone has signaled
> -   an error and the process wasn't started successfully, so we should
> -   remove it from the process list.  */
> +/* If PROC doesn't have its pid set, then an error was signaled and
> +   the process wasn't started successfully, so remove it.  */
>  static void
>  start_process_unwind (Lisp_Object proc)
>  {
> -  if (!PROCESSP (proc))
> -    emacs_abort ();
> -
> -  /* Was PROC started successfully?
> -     -2 is used for a pty with no process, eg for gdb.  */
>    if (XPROCESS (proc)->pid <= 0 && XPROCESS (proc)->pid != -2)
>      remove_process (proc);
>  }
> @@ -3124,7 +3110,6 @@ connect_network_socket (Lisp_Object proc, Lisp_Object addrinfos,
>                          Lisp_Object use_external_socket_p)
>  {
>    ptrdiff_t count = SPECPDL_INDEX ();
> -  ptrdiff_t count1;
>    int s = -1, outch, inch;
>    int xerrno = 0;
>    int family;
> @@ -3145,7 +3130,6 @@ connect_network_socket (Lisp_Object proc, Lisp_Object addrinfos,
>      }
>  
>    /* Do this in case we never enter the while-loop below.  */
> -  count1 = SPECPDL_INDEX ();
>    s = -1;
>  
>    while (!NILP (addrinfos))
> @@ -3313,7 +3297,7 @@ connect_network_socket (Lisp_Object proc, Lisp_Object addrinfos,
>        immediate_quit = 0;
>  
>        /* Discard the unwind protect closing S.  */
> -      specpdl_ptr = specpdl + count1;
> +      specpdl_ptr = specpdl + count;
>        emacs_close (s);
>        s = -1;
>        if (0 <= socket_to_use)
> @@ -3398,10 +3382,7 @@ connect_network_socket (Lisp_Object proc, Lisp_Object addrinfos,
>    p->outfd = outch;
>  
>    /* Discard the unwind protect for closing S, if any.  */
> -  specpdl_ptr = specpdl + count1;
> -
> -  /* Unwind bind_polling_period and request_sigio.  */
> -  unbind_to (count, Qnil);
> +  specpdl_ptr = specpdl + count;
>  
>    if (p->is_server && p->socktype != SOCK_DGRAM)
>      pset_status (p, Qlisten);
> @@ -3925,7 +3906,12 @@ usage: (make-network-process &rest ARGS)  */)
>  
>    if (!NILP (buffer))
>      buffer = Fget_buffer_create (buffer);
> +
> +  /* Unwind bind_polling_period.  */
> +  unbind_to (count, Qnil);
> +
>    proc = make_process (name);
> +  record_unwind_protect (remove_process, proc);
>    p = XPROCESS (proc);
>    pset_childp (p, contact);
>    pset_plist (p, Fcopy_sequence (Fplist_get (contact, QCplist)));
> @@ -3956,8 +3942,6 @@ usage: (make-network-process &rest ARGS)  */)
>  
>    set_network_socket_coding_system (proc, host, service, name);
>  
> -  unbind_to (count, Qnil);
> -
>    /* :server BOOL */
>    tem = Fplist_get (contact, QCserver);
>    if (!NILP (tem))
> @@ -3974,6 +3958,7 @@ usage: (make-network-process &rest ARGS)  */)
>        && !NILP (Fplist_get (contact, QCnowait)))
>      p->is_non_blocking_client = true;
>  
> +  bool postpone_connection = false;
>  #ifdef HAVE_GETADDRINFO_A
>    /* With async address resolution, the list of addresses is empty, so
>       postpone connecting to the server. */
> @@ -3981,11 +3966,13 @@ usage: (make-network-process &rest ARGS)  */)
>      {
>        p->dns_request = dns_request;
>        p->status = list1 (Qconnect);
> -      return proc;
> +      postpone_connection = true;
>      }
>  #endif
> +  if (! postpone_connection)
> +    connect_network_socket (proc, addrinfos, use_external_socket_p);
>  
> -  connect_network_socket (proc, addrinfos, use_external_socket_p);
> +  specpdl_ptr = specpdl + count;
>    return proc;
>  }
>  
> diff --git a/src/process.h b/src/process.h
> index 6c227bc..9926050 100644
> --- a/src/process.h
> +++ b/src/process.h
> @@ -118,10 +118,11 @@ struct Lisp_Process
>      /* After this point, there are no Lisp_Objects any more.  */
>      /* alloc.c assumes that `pid' is the first such non-Lisp slot.  */
>  
> -    /* Number of this process.
> -       allocate_process assumes this is the first non-Lisp_Object field.
> -       A value 0 is used for pseudo-processes such as network or serial
> -       connections.  */
> +    /* Process ID.  A positive value is a child process ID.
> +       Zero is for pseudo-processes such as network or serial connections,
> +       or for processes that have not been fully created yet.
> +       -1 is for a process that was not created successfully.
> +       -2 is for a pty with no process, e.g., for GDB.  */
>      pid_t pid;
>      /* Descriptor by which we read from this process.  */
>      int infd;

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no