GNU bug report logs - #15075
24.3.50; Infinite loop when closing some connections

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 14:36:33 +0200

When reading (via tls) from pop3, Emacs hangs hard upon closing the
connection.

strace says:

[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)
[pid 18991] read(17, 0x7fff4c6ac3f0, 4096) = -1 EBADF (Bad file descriptor)

/proc shows that fd 17 no longer exists, so it's probably been closed by
Emacs, and we're then inflooping in a read on that socket, for some
reason,

The last checkin is:

fixes bug: http://debbugs.gnu.org/15035
committer: Paul Eggert <eggert <at> cs.ucla.edu>
branch nick: trunk
timestamp: Mon 2013-08-12 00:12:07 -0700
message:
  Fix some fd issues when running subprocesses.

So that seems like a likely candidate.  :-)

Here's the gdb backtrace:

#0  0x00007ffff2f4718d in read () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00000000004e5086 in read (__nbytes=4096, __buf=0x7fffffffa340, __fd=21) at /usr/include/x86_64-linux-gnu/bits/unistd.h:45
#2  emacs_read (fildes=fildes <at> entry=21, buf=0x7fffffffa340 "+OK Logging out, messages deleted.\r\n", nbyte=4096) at sysdep.c:2300
#3  0x0000000000577820 in read_process_output (proc=proc <at> entry=26878253, channel=21) at process.c:4980
#4  0x000000000057c548 in wait_reading_process_output (time_limit=<optimized out>, nsecs=-1, read_kbd=read_kbd <at> entry=0, 
    do_display=do_display <at> entry=false, wait_for_cell=11969090, wait_proc=0x19a2128, just_wait_proc=0) at process.c:4435
#5  0x000000000057d541 in Faccept_process_output (process=26878253, seconds=<optimized out>, millisec=<optimized out>, 
    just_this_one=<optimized out>) at process.c:3948
#6  0x000000000053fb44 in Ffuncall (nargs=<optimized out>, args=<optimized out>) at eval.c:2864
#7  0x0000000000573b7b in exec_byte_code (bytestr=-9, vector=140737488331584, maxdepth=4096, args_template=140737488337176, 
    nargs=4611686018662268928, args=0x400000003f000000) at bytecode.c:905
#8  0x000000000053f5f1 in funcall_lambda (fun=25388357, nargs=nargs <at> entry=1, arg_vector=arg_vector <at> entry=0x7fffffffbaa0) at eval.c:3087
#9  0x000000000053f953 in Ffuncall (nargs=2, args=0x7fffffffba98) at eval.c:2914
#10 0x0000000000573b7b in exec_byte_code (bytestr=-9, vector=140737488331584, maxdepth=4096, args_template=0, nargs=4611686018662268928, 
    args=0x400000003f000000) at bytecode.c:905




In GNU Emacs 24.3.50.8 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2013-08-12 on stories
Bzr revision: 113815 rgm <at> gnu.org-20130812101743-djba3ieqivg87pnd
Windowing system distributor `The X.Org Foundation', version 11.0.11204000
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-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #8 received at 15075 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: 15075 <at> debbugs.gnu.org
Subject: Re: bug#15075: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 15:08:50 +0200

It happened again -- this time when sending and email via SMTP + TLS.

strace output:

[pid 19377] read(17, 0x7ffff03e9bb0, 4096) = -1 EBADF (Bad file descriptor)
[pid 19377] read(17, 0x7ffff03e9bb0, 4096) = -1 EBADF (Bad file descriptor)
[pid 19377] read(17, 0x7ffff03e9bb0, 4096) = -1 EBADF (Bad file descriptor)
[pid 19377] read(17, 0x7ffff03e9bb0, 4096) = -1 EBADF (Bad file descriptor)
[pid 19377] read(17, 0x7ffff03e9bb0, 4096) = -1 EBADF (Bad file descriptor)
[pid 19377] read(17, 0x7ffff03e9bb0, 4096) = -1 EBADF (Bad file descriptor)

fd 17 again?  That's an odd coincidence...

-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #11 received at 15075 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: 15075 <at> debbugs.gnu.org
Subject: Re: bug#15075: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 15:22:05 +0200

Lars Magne Ingebrigtsen <larsi <at> gnus.org> writes:

> fd 17 again?  That's an odd coincidence...

Yeah, just a coincidence.  Here's the next hang upon sending an email:

[pid 20227] read(20, 0x7fff7389a190, 4096) = -1 EBADF (Bad file descriptor)
[pid 20227] read(20, 0x7fff7389a190, 4096) = -1 EBADF (Bad file descriptor)
[pid 20227] read(20, 0x7fff7389a190, 4096) = -1 EBADF (Bad file descriptor)
[pid 20227] read(20, 0x7fff7389a190, 4096) = -1 EBADF (Bad file descriptor)
[pid 20227] read(20, 0x7fff7389a190, 4096) = -1 EBADF (Bad file descriptor)
[pid 20227] read(20, 0x7fff7389a190, 4096) = -1 EBADF (Bad file descriptor)


-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #14 received at 15075 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: 15075 <at> debbugs.gnu.org
Subject: Re: bug#15075: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 17:22:41 +0200

Here's another gdb backtrace from when it hangs.  Hm...  Ok, I should
probably re-compile it with -O2.  I'll do that and get another hang.

0  0x00007ffff2f4718d in read () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x00000000004e5086 in read (__nbytes=4096, __buf=0x7fffffffb6d0, __fd=21) at /usr/include/x86_64-linux-gnu/bits/unistd.h:45
#2  emacs_read (fildes=fildes <at> entry=21, buf=0x7fffffffb6d0 "221 hermes.netfonds.no closing connection\r\n", nbyte=4096) at sysdep.c:2300
#3  0x0000000000577820 in read_process_output (proc=proc <at> entry=85871045, channel=21) at process.c:4980
#4  0x000000000057c548 in wait_reading_process_output (time_limit=<optimized out>, nsecs=-1, read_kbd=read_kbd <at> entry=0, 
    do_display=do_display <at> entry=false, wait_for_cell=11969090, wait_proc=0x51e49c0, just_wait_proc=0) at process.c:4435
#5  0x000000000057d541 in Faccept_process_output (process=85871045, seconds=<optimized out>, millisec=<optimized out>, 
    just_this_one=<optimized out>) at process.c:3948

-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #17 received at 15075 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: 15075 <at> debbugs.gnu.org
Subject: Re: bug#15075: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 17:24:23 +0200

Hey, that was fast.

This bug isn't reliably repeatable, so it may be timing-related or
something.  But here's an -O0 build:

0  0x00007ffff2f4718d in read () from /lib/x86_64-linux-gnu/libpthread.so.0
#1  0x0000000000536ea3 in emacs_read (fildes=21, buf=0x7fffffff8830 "221 hermes.netfonds.no closing connection\r\n", nbyte=4096)
    at sysdep.c:2300
#2  0x00000000005f88c5 in read_process_output (proc=71750957, channel=21) at process.c:4980
#3  0x00000000005f71c3 in wait_reading_process_output (time_limit=0, nsecs=-1, read_kbd=0, do_display=false, wait_for_cell=12567106, 
    wait_proc=0x446d528, just_wait_proc=0) at process.c:4435
#4  0x00000000005f5f7f in Faccept_process_output (process=71750957, seconds=12567106, millisec=12567106, just_this_one=12567106)
    at process.c:3948
#5  0x00000000005abeea in Ffuncall (nargs=2, args=0x7fffffff9da8) at eval.c:2864
#6  0x00000000005ebce6 in exec_byte_code (bytestr=70546449, vector=72148261, maxdepth=20, args_template=12567106, nargs=0, args=0x0)
    at bytecode.c:905
#7  0x00000000005eb185 in Fbyte_code (bytestr=70546449, vector=72148261, maxdepth=20) at bytecode.c:478
#8  0x00000000005aaa4a in eval_sub (form=72367398) at eval.c:2229
#9  0x00000000005a8722 in internal_catch (tag=16167106, func=0x5aa416 <eval_sub>, arg=72367398) at eval.c:1113
#10 0x00000000005ecad6 in exec_byte_code (bytestr=68666769, vector=72148485, maxdepth=20, args_template=12567106, nargs=0, args=0x0)
    at bytecode.c:1086
#11 0x00000000005ac857 in funcall_lambda (fun=72148573, nargs=1, arg_vector=0x44ce605) at eval.c:3087
#12 0x00000000005ac04c in Ffuncall (nargs=2, args=0x7fffffffa8f8) at eval.c:2902
#13 0x00000000005ebce6 in exec_byte_code (bytestr=75448801, vector=72146685, maxdepth=12, args_template=12567106, nargs=0, args=0x0)
    at bytecode.c:905
#14 0x00000000005eb185 in Fbyte_code (bytestr=75448801, vector=72146685, maxdepth=12) at bytecode.c:478
#15 0x00000000005aaa4a in eval_sub (form=72371078) at eval.c:2229
#16 0x00000000005a74ce in Fprogn (body=72369206) at eval.c:460
#17 0x00000000005a750c in unwind_body (body=72369206) at eval.c:474

-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #20 received at 15075 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: 15075 <at> debbugs.gnu.org
Subject: Re: bug#15075: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 17:28:51 +0200

With an -O0 build, it's almost completely repeatable.

Here's the accompanying Lisp backtrace.  So it seems like we're sending
via gnutls, we send the quit command to the SMTP server, it says "bye"
and closes the connection, and then the next (?) call to
`accept-process-output' infloops.

Lisp Backtrace:
"accept-process-output" (0xffff9db0)
"byte-code" (0xffffa1b0)
"smtpmail-read-response" (0xffffa900)
"byte-code" (0xffffacf0)
"smtpmail-via-smtp" (0xffffb420)
"smtpmail-send-it" (0xffffb910)
"message-smtpmail-send-it" (0xffffbdd0)
"message-multi-smtp-send-mail" (0xffffc2a0)
"gnus-agent-send-mail" (0xffffc770)
"message-send-mail" (0xffffcc70)
"message-send-via-mail" (0xffffd130)
"message-send" (0xffffd610)
"message-send-and-exit" (0xffffdb18)
"call-interactively" (0xffffde30)
"command-execute" (0xffffe318)


-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #23 received at 15075 <at> debbugs.gnu.org (full text, mbox):

From: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
To: 15075 <at> debbugs.gnu.org
Subject: Re: bug#15075: 24.3.50; Infinite loop when closing some connections
Date: Mon, 12 Aug 2013 18:04:56 +0200

This is what's hanging.  If we get any other errors than EIO, EAGAIN or
EWOULDBLOCK, then we infloop here.  And we get EBADF, so this infloops.

	  /* Read data from the process, until we exhaust it.  */
	  while (wait_proc->infd >= 0)
	    {
	      int nread = read_process_output (proc, wait_proc->infd);

	      if (nread == 0)
		break;

	      if (nread > 0)
		got_some_input = read_some_bytes = 1;
	      else if (nread == -1 && (errno == EIO || errno == EAGAIN))
		break;
#ifdef EWOULDBLOCK
	      else if (nread == -1 && EWOULDBLOCK == errno)
		break;
#endif
	    }

I'm guessing that something is supposed to set wait_proc->infd something
smaller than zero somewhere if a serious error happens.

Yup:

(gdb) print wait_proc->open_fd
$12 = {-1, -1, -1, -1, -1, -1}
(gdb) print wait_proc->infd   
$13 = 21

And this looks like the likely culprit:

-      p->infd  = -1;
-      p->outfd = -1;
+  for (i = 0; i < PROCESS_OPEN_FDS; i++)
+    close_process_fd (&p->open_fd[i]);

So there's some disagreement about what's saying whether sockets are
open or not, and if the closing happens at the wrong time, we infloop.

-- 
(domestic pets only, the antidote for overdose, milk.)
  No Gnus T-Shirt for sale: http://ingebrigtsen.no/no.php
  and http://lars.ingebrigtsen.no/2013/08/twenty-years-of-september.html

Message #28 received at 15075-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Lars Magne Ingebrigtsen <larsi <at> gnus.org>
Cc: 15075-done <at> debbugs.gnu.org
Subject: Re: trunk r113824: * process.c (deactivate_process): Reset fds to -1.
Date: Mon, 12 Aug 2013 19:44:03 -0700

Lars Magne Ingebrigtsen wrote:
> Does this fix bug#15075, too?

Yes, I think trunk bzr 113824 should also fix
bug#15075.  I'll CC: this to 15075 <at> debbugs.gnu.org
to give them a heads up.  I'm taking the liberty of
closing that bug; if I'm wrong, please reopen it or
let me know and I'll reopen it.

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