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Pedro Alves 23f238d345 Fix race exposed by gdb.threads/killed.exp
On GNU/Linux, this test sometimes FAILs like this:

 (gdb) run
 Starting program: /home/pedro/gdb/mygit/build/gdb/testsuite/gdb.threads/killed
 [Thread debugging using libthread_db enabled]
 Using host libthread_db library "/lib64/libthread_db.so.1".
 ptrace: No such process.
 (gdb)
 Program terminated with signal SIGKILL, Killed.
 The program no longer exists.
 FAIL: gdb.threads/killed.exp: run program to completion (timeout)

Note the suspicious "No such process" line (that's errno==ESRCH).
Adding debug output we see:

  linux_nat_wait: [process -1], [TARGET_WNOHANG]
  LLW: enter
  LNW: waitpid(-1, ...) returned 18465, ERRNO-OK
  LLW: waitpid 18465 received Stopped (signal) (stopped)
  LNW: waitpid(-1, ...) returned 18461, ERRNO-OK
  LLW: waitpid 18461 received Trace/breakpoint trap (stopped)
  LLW: Handling extended status 0x03057f
  LHEW: Got clone event from LWP 18461, new child is LWP 18465
  LNW: waitpid(-1, ...) returned 0, ERRNO-OK
  RSRL: resuming stopped-resumed LWP LWP 18465 at 0x3b36af4b51: step=0
  RSRL: resuming stopped-resumed LWP LWP 18461 at 0x3b36af4b51: step=0
  sigchld
  ptrace: No such process.
  (gdb) linux_nat_wait: [process -1], [TARGET_WNOHANG]
  LLW: enter
  LNW: waitpid(-1, ...) returned 18465, ERRNO-OK
  LLW: waitpid 18465 received Killed (terminated)
  LLW: LWP 18465 exited.
  LNW: waitpid(-1, ...) returned 18461, No child processes
  LLW: waitpid 18461 received Killed (terminated)
  Process 18461 exited
  LNW: waitpid(-1, ...) returned -1, No child processes
  LLW: exit
  sigchld
  infrun: target_wait (-1, status) =
  infrun:   18461 [process 18461],
  infrun:   status->kind = signalled, signal = GDB_SIGNAL_KILL
  infrun: TARGET_WAITKIND_SIGNALLED

  Program terminated with signal SIGKILL, Killed.
  The program no longer exists.
  infrun: stop_waiting
  FAIL: gdb.threads/killed.exp: run program to completion (timeout)

The issue is that here:

  RSRL: resuming stopped-resumed LWP LWP 18465 at 0x3b36af4b51: step=0
  RSRL: resuming stopped-resumed LWP LWP 18461 at 0x3b36af4b51: step=0

The first line shows we had just resumed LWP 18465, which does:

 void *
 child_func (void *dummy)
 {
   kill (pid, SIGKILL);
   exit (1);
 }

So if the kernel manages to schedule that thread fast enough, the
process may be killed before GDB has a chance to resume LWP 18461.

GDBserver has code at the tail end of linux_resume_one_lwp to cope
with this:

~~~
    ptrace (step ? PTRACE_SINGLESTEP : PTRACE_CONT, lwpid_of (thread),
	    (PTRACE_TYPE_ARG3) 0,
	    /* Coerce to a uintptr_t first to avoid potential gcc warning
	       of coercing an 8 byte integer to a 4 byte pointer.  */
	    (PTRACE_TYPE_ARG4) (uintptr_t) signal);

    current_thread = saved_thread;
    if (errno)
      {
	/* ESRCH from ptrace either means that the thread was already
	   running (an error) or that it is gone (a race condition).  If
	   it's gone, we will get a notification the next time we wait,
	   so we can ignore the error.  We could differentiate these
	   two, but it's tricky without waiting; the thread still exists
	   as a zombie, so sending it signal 0 would succeed.  So just
	   ignore ESRCH.  */
	if (errno == ESRCH)
	  return;

	perror_with_name ("ptrace");
      }
~~~

However, that's not a complete fix, because between starting to handle
the resume request and getting that PTRACE_CONTINUE, we run other
ptrace calls that can also fail with ESRCH, and that end up throwing
an error (with perror_with_name).

In the case above, I indeed sometimes see resume_stopped_resumed_lwps
fail in the registers read:

resume_stopped_resumed_lwps (struct lwp_info *lp, void *data)
{
...
      CORE_ADDR pc = regcache_read_pc (regcache);

Or e.g., in 32-bit mode, i386_linux_resume has several calls that can
throw too.

Whether to ignore ptrace errors or not depends on context that is only
available somewhere up the call chain.  So the fix is to let ptrace
errors throw as they do today, and wrap the resume request in a
TRY/CATCH that swallows it iff the lwp that we were trying to resume
is no longer ptrace-stopped.

gdb/gdbserver/ChangeLog:
2015-03-19  Pedro Alves  <palves@redhat.com>

	* linux-low.c (linux_resume_one_lwp): Rename to ...
	(linux_resume_one_lwp_throw): ... this.  Don't handle ESRCH here,
	instead call perror_with_name.
	(check_ptrace_stopped_lwp_gone): New function.
	(linux_resume_one_lwp): Reimplement as wrapper around
	linux_resume_one_lwp_throw that swallows errors if the LWP is
	gone.

gdb/ChangeLog:
2015-03-19  Pedro Alves  <palves@redhat.com>

	* linux-nat.c (linux_resume_one_lwp): Rename to ...
	(linux_resume_one_lwp_throw): ... this.  Don't handle ESRCH here,
	instead call perror_with_name.
	(check_ptrace_stopped_lwp_gone): New function.
	(linux_resume_one_lwp): Reimplement as wrapper around
	linux_resume_one_lwp_throw that swallows errors if the LWP is
	gone.
	(resume_stopped_resumed_lwps): Try register reads in TRY/CATCH and
	swallows errors if the LWP is gone.  Use
	linux_resume_one_lwp_throw instead of linux_resume_one_lwp.
2015-03-19 17:07:38 +00:00
bfd Add support for G13 and G14 flag bits in RL78 ELF binaries. 2015-03-19 15:37:43 +00:00
binutils Add support for G13 and G14 flag bits in RL78 ELF binaries. 2015-03-19 15:37:43 +00:00
config Sync isl.m4 with GCC tree 2015-03-16 08:51:37 -07:00
cpu or1k: add missing l.msync, l.psync and l.psync instructions. 2014-07-20 20:26:09 +03:00
elfcpp [gold] Recognize DWARF5/GCC5 DW_LANG_Fortran03 and DW_LANG_Fortran08. 2015-02-17 08:08:24 +01:00
etc PR external/{16327,16328}: Remove etc/configure.texi and etc/standards.texi. 2014-06-27 11:33:25 +02:00
gas Add support for G13 and G14 flag bits in RL78 ELF binaries. 2015-03-19 15:37:43 +00:00
gdb Fix race exposed by gdb.threads/killed.exp 2015-03-19 17:07:38 +00:00
gold Fix gold incremental test failures. 2015-03-11 22:07:51 -07:00
gprof Regenerate Makeile.in file for copyright update 2015-01-02 22:27:27 +10:30
include Add support for G13 and G14 flag bits in RL78 ELF binaries. 2015-03-19 15:37:43 +00:00
intl
ld Use %F instead of %X for einfo 2015-03-18 11:45:12 +10:30
libdecnumber Another part of fixing "make TAGS". 2015-01-22 21:07:31 +02:00
libiberty strerror.c: Do not declare sys_nerr or sys_errlist if already macros 2015-01-19 16:29:07 +01:00
opcodes Add znver1 processor 2015-03-17 21:49:15 +05:30
readline Fix executable indicator in file name completion on Windows. 2014-12-30 21:14:25 +02:00
sim sim/erc32: Removed type mismatch compiler warnings 2015-03-17 18:58:14 -04:00
texinfo
.cvsignore
.gitattributes Add a .gitattributes file for use with git-merge-changelog 2014-07-25 18:07:23 -04:00
.gitignore
ChangeLog Exclude target-zlib if target-libjava isn't built 2015-03-17 17:07:22 -07:00
compile Update from upstream Automake 2014-11-16 13:43:48 +01:00
config-ml.in Sync config-ml.in with GCC trunk 2015-03-17 05:15:34 -07:00
config.guess config.sub, config.guess: Update from upstream, to 2015-01-01 version. 2015-01-02 10:40:57 +01:00
config.rpath
config.sub config.sub, config.guess: Update from upstream, to 2015-01-01 version. 2015-01-02 10:40:57 +01:00
configure Exclude target-zlib if target-libjava isn't built 2015-03-17 17:07:22 -07:00
configure.ac Exclude target-zlib if target-libjava isn't built 2015-03-17 17:07:22 -07:00
COPYING
COPYING3
COPYING3.LIB
COPYING.LIB
COPYING.LIBGLOSS
COPYING.NEWLIB
depcomp Update from upstream Automake 2014-11-16 13:43:48 +01:00
djunpack.bat
install-sh Update from upstream Automake 2014-11-16 13:43:48 +01:00
libtool.m4 Update libtool.m4 from GCC trunk 2014-11-24 09:14:09 -08:00
lt~obsolete.m4
ltgcc.m4
ltmain.sh
ltoptions.m4
ltsugar.m4
ltversion.m4
MAINTAINERS Update description of ownership of files in include/ 2014-11-04 16:14:14 -08:00
Makefile.def Update top-level files from GCC trunk 2015-03-16 09:12:37 -07:00
Makefile.in Update top-level files from GCC trunk 2015-03-16 09:12:37 -07:00
Makefile.tpl Update top-level files from GCC trunk 2015-03-16 09:12:37 -07:00
makefile.vms
missing Update from upstream Automake 2014-11-16 13:43:48 +01:00
mkdep
mkinstalldirs Update from upstream Automake 2014-11-16 13:43:48 +01:00
move-if-change Update `move-if-change' from gnulib 2014-11-16 17:04:02 +01:00
README
README-maintainer-mode
setup.com
src-release.sh src-release.sh: configure using --target. 2014-10-15 09:50:53 +02:00
symlink-tree
ylwrap Update from upstream Automake 2014-11-16 13:43:48 +01:00

		   README for GNU development tools

This directory contains various GNU compilers, assemblers, linkers, 
debuggers, etc., plus their support routines, definitions, and documentation.

If you are receiving this as part of a GDB release, see the file gdb/README.
If with a binutils release, see binutils/README;  if with a libg++ release,
see libg++/README, etc.  That'll give you info about this
package -- supported targets, how to use it, how to report bugs, etc.

It is now possible to automatically configure and build a variety of
tools with one command.  To build all of the tools contained herein,
run the ``configure'' script here, e.g.:

	./configure 
	make

To install them (by default in /usr/local/bin, /usr/local/lib, etc),
then do:
	make install

(If the configure script can't determine your type of computer, give it
the name as an argument, for instance ``./configure sun4''.  You can
use the script ``config.sub'' to test whether a name is recognized; if
it is, config.sub translates it to a triplet specifying CPU, vendor,
and OS.)

If you have more than one compiler on your system, it is often best to
explicitly set CC in the environment before running configure, and to
also set CC when running make.  For example (assuming sh/bash/ksh):

	CC=gcc ./configure
	make

A similar example using csh:

	setenv CC gcc
	./configure
	make

Much of the code and documentation enclosed is copyright by
the Free Software Foundation, Inc.  See the file COPYING or
COPYING.LIB in the various directories, for a description of the
GNU General Public License terms under which you can copy the files.

REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info
on where and how to report problems.