As discussed in libc-alpha [1] current clone with CLONE_VM (without
CLONE_THREAD set) will reset the pthread pid/tid fields to -1. The
issue is since memory is shared between the parent and child it will
clobber parent's cached pid/tid leading to internal inconsistencies
if the value is not restored.
And even it is restored it may lead to racy conditions when between
set/restore a thread might invoke pthread function that validate the
pthread with INVALID_TD_P/INVALID_NOT_TERMINATED_TD_P and thus get
wrong results.
As stated in BZ19957, previously reports of this behaviour was close
with EWONTFIX due the fact usage of clone outside glibc is tricky
since glibc requires consistent internal pthread, while using clone
directly may not provide it. However since now posix_spawn uses
clone (CLONE_VM) to fixes various issues related to previous vfork
usage this issue requires fixing.
The vfork implementation also does something similar, but instead
it negates and restores only the *pid* field and functions that
might access its value know to handle such case (getpid, raise
and pthread ones that uses INVALID_TD_P/INVALID_NOT_TERMINATED_TD_P
macros that check only *tid* field). Also vfork does not call
__clone directly, instead calling either __NR_vfork or __NR_clone
directly.
So this patch removes this clone behavior by avoiding setting
the pthread pid/tid field for CLONE_VM. There is no need to
check for CLONE_THREAD, since the minimum supported kernel in all
architecture implies that CLONE_VM must be used with CLONE_THREAD,
otherwise clone returns EINVAL.
Instead of current approach of:
int clone(int (*fn)(void *), void *child_stack, int flags, ...)
[...]
if (flags & CLONE_THREAD)
goto do_syscall;
pid_t new_value;
if (flags & CLONE_VM)
new_value = -1;
else
new_value = getpid ();
THREAD_SETMEM (THREAD_SELF, pid, new_value);
THREAD_SETMEM (THREAD_SELF, tid, new_value);
do_syscall:
[...]
The new approach uses:
int clone(int (*fn)(void *), void *child_stack, int flags, ...)
[...]
if (flags & CLONE_VM)
goto do_syscall;
pid_t new_value = getpid ();
THREAD_SETMEM (THREAD_SELF, pid, new_value);
THREAD_SETMEM (THREAD_SELF, tid, new_value);
do_syscall:
[...]
It also removes the linux tst-getpid2.c test which expects the previous
behavior and instead add another clone test.
Tested on x86_64, i686, x32, powerpc64le, aarch64, armhf, s390, and
s390x. I also did limited check on mips32 and sparc64 (using the new
added test).
I also got reviews from both m68k, hppa, and tile. So I presume for
these architecture the patch works.
The fixes for alpha, microblaze, sh, ia64, and nio2 have not been
tested.
[1] https://sourceware.org/ml/libc-alpha/2016-04/msg00307.html
* sysdeps/unix/sysv/linux/Makefile [$(subdir) == nptl] (test): Remove
tst-getpid2.
(test): Add tst-clone2.
* sysdeps/unix/sysv/linux/tst-clone2.c: New file.
* sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Do not change
pid/tid fields for CLONE_VM.
* sysdeps/unix/sysv/linux/arm/clone.S: Likewise.
* sysdeps/unix/sysv/linux/i386/clone.S: Likewise.
* sysdeps/unix/sysv/linux/mips/clone.S: Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S: Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S: Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/clone.S: Likewise.
* sysdeps/unix/sysv/linux/s390/s390-64/clone.S: Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S: Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S: Likewise.
* sysdeps/unix/sysv/linux/x86_64/clone.S: Likewise.
* sysdeps/unix/sysv/linux/tst-getpid2.c: Remove file.
This patch implements a new posix_spawn{p} implementation for Linux. The main
difference is it uses the clone syscall directly with CLONE_VM and CLONE_VFORK
flags and a direct allocated stack. The new stack and start function solves
most the vfork limitation (possible parent clobber due stack spilling). The
remaning issue are related to signal handling:
1. That no signal handlers must run in child context, to avoid corrupt
parent's state.
2. Child must synchronize with parent to enforce stack deallocation and
to possible return execv issues.
The first one is solved by blocking all signals in child, even NPTL-internal
ones (SIGCANCEL and SIGSETXID). The second issue is done by a stack allocation
in parent and a synchronization with using a pipe or waitpid (in case or error).
The pipe has the advantage of allowing the child signal an exec error (checked
with new tst-spawn2 test).
There is an inherent race condition in pipe2 usage for architectures that do not
support the syscall directly. In such cases the a pipe plus fctnl is used
instead and it may lead to file descriptor leak in parent (as decribed by fcntl
documentation).
The child process stack is allocate with a mmap with MAP_STACK flag using
default architecture stack size. Although it is slower than use a stack buffer
from parent, it allows some slack for the compatibility code to run scripts
with no shebang (which may use a buffer with size depending of argument list
count).
Performance should be similar to the vfork default posix implementation and
way faster than fork path (vfork on mostly linux ports are basically
clone with CLONE_VM plus CLONE_VFORK). The only difference is the syscalls
required for the stack allocation/deallocation.
It fixes BZ#10354, BZ#14750, and BZ#18433.
Tested on i386, x86_64, powerpc64le, and aarch64.
[BZ #14750]
[BZ #10354]
[BZ #18433]
* include/sched.h (__clone): Add hidden prototype.
(__clone2): Likewise.
* include/unistd.h (__dup): Likewise.
* posix/Makefile (tests): Add tst-spawn2.
* posix/tst-spawn2.c: New file.
* sysdeps/posix/dup.c (__dup): Add hidden definition.
* sysdeps/unix/sysv/linux/aarch64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/alpha/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/arm/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/hppa/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/i386/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/ia64/clone2.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/m68k/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/microblaze/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/mips/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/nios2/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S (__clone):
Likewise.
* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S (__clone):
Likewise.
* sysdeps/unix/sysv/linux/s390/s390-32/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/s390/s390-64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sh/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/tile/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/x86_64/clone.S (__clone): Likewise.
* sysdeps/unix/sysv/linux/nptl-signals.h
(____nptl_is_internal_signal): New function.
* sysdeps/unix/sysv/linux/spawni.c: New file.
I've moved the MIPS port from ports to the main sysdeps hierarchy.
Beyond the README update, the move of the files was simply
git mv ports/sysdeps/mips sysdeps/mips
git mv ports/sysdeps/unix/mips sysdeps/unix/mips
git mv ports/sysdeps/unix/sysv/linux/mips sysdeps/unix/sysv/linux/mips
and in addition to the ChangeLog entries here, I put a note at the top
of ports/ChangeLog.mips similar to those in other files.
Tested that disassembly of installed shared libraries for mips is the
same before and after this patch (except for ld.so where paths in
assertions are involved, as for arm).
* sysdeps/mips: Move directory from ports/sysdeps/mips.
* sysdeps/unix/mips: Move directory from ports/sysdeps/unix/mips.
* sysdeps/unix/sysv/linux/mips: Move directory from
ports/sysdeps/unix/sysv/linux/mips.
* README: Update listing for mips-*-linux-gnu and
mips64-*-linux-gnu.
* sysdeps/mips: Move directory to ../sysdeps/mips.
* sysdeps/unix/mips: Move directory to ../sysdeps/unix/mips.
* sysdeps/unix/sysv/linux/mips: Move directory to
../sysdeps/unix/sysv/linux/mips.
2003-03-11 Ralf Baechle <ralf@linux-mips.org>
* sysdeps/unix/sysv/linux/mips/clone.S (__thread_start): Use jal
instead of jalr to invoke subroutine so restoring the $gp register
will work properly.
2001-07-06 Paul Eggert <eggert@twinsun.com>
* manual/argp.texi: Remove ignored LGPL copyright notice; it's
not appropriate for documentation anyway.
* manual/libc-texinfo.sh: "Library General Public License" ->
"Lesser General Public License".
2001-07-06 Andreas Jaeger <aj@suse.de>
* All files under GPL/LGPL version 2: Place under LGPL version
2.1.
2000-02-10 Andreas Jaeger <aj@suse.de>
* sysdeps/unix/sysv/linux/mips/clone.S: Rewritten.
Based on a patch by Hiroyuki Machida <machida@sm.sony.co.jp>.
1997-07-26 04:14 Ulrich Drepper <drepper@cygnus.com>
* elf/Makefile (distribute): Add genrtldtbl.awk.
(before-compile): Add rtldtbl.h.
(GAWK): New variable.
(generated): Add trusted-dirs.h and rtldtbl.h.
($(objpfx)rtldtbl.h): New rule. File is needed by dl-load.c.
* elf/dl-load.c: Rewrite. Now use cache and look for shared
objects in machine dependent directories.
* elf/dl-object.c (_dl_new_object): Initialize l_rpath_dirs member.
* elf/dl-support.c: Rename function to non_dynamic_init and add
initialization for _dl_platform, _dl_platformlen, _dl_pagesize
and call to initializer for search path.
* elf/elf.h: Add AT_PLATFORM and AT_HWCAP.
* elf/genrtldtbl.awk: New file.
* elf/link.h: Add type definitions and declarations for search
path cache.
* elf/rtld.c: Add definitions of variables used for search path cache.
* sysdeps/generic/dl-sysdep.c: Let auxiliary vector initialize
_dl_platform. Initialize _dl_pagesize early and use this value.
* sysdeps/i386/dl-machine.h: Add code for _dl_platform handling.
* sysdeps/mach/hurd/dl-sysdep.c: Initialize _dl_pagesize.
* sysdeps/unix/sysv/linux/dl-sysdep.c: Use _dl_pagesize instead
of calling getpagesize.
* elf/dl-error.c (_dl_signal_error): Make message nicer.
* nss/libnss_files.map: Fix typo.
Reported by Thorsten Kukuk <kukuk@vt.uni-paderborn.de>.
* sysdeps/generic/strsep.c: Optimize case where separator set contains
only one character.
* sysdeps/libm-ieee754/s_ccosh.c: Correct sign of result for real
== +-Inf.
* sysdeps/libm-ieee754/s_ccoshf.c: Likewise.
* sysdeps/libm-ieee754/s_ccoshl.c: Likewise.
1997-07-25 09:15 H.J. Lu <hjl@gnu.ai.mit.edu>
* sysdeps/sparc/udiv_qrnnd.S: Check PIC instead of __PIC__.
* sysdeps/unix/sysv/linux/sparc/__sigtrampoline.S: Likewise.
* sysdeps/unix/mips/sysdep.S: Likewise.
* sysdeps/unix/sysv/linux/mips/clone.S: Likewise.
* sysdeps/mips/bsd-_setjmp.S: Remove __PIC__ comment.
* sysdeps/mips/bsd-setjmp.S: Likewise.
* sysdeps/mips/dl-machine.h: Remove extra stuff.
* sysdeps/mips/mips64/dl-machine.h: Likewise.
1997-07-25 18:55 Philip Blundell <Philip.Blundell@pobox.com>
* sysdeps/standalone/arm/sysdep.c: New file.
1997-07-25 13:25 Philip Blundell <Philip.Blundell@pobox.com>
* aout/Makefile: New file.
* Makeconfig (binfmt-subdir): Assume a.out when not ELF.
* sysdeps/generic/machine-gmon.h: Add warning about limitations of
__builtin_return_address().
* sysdeps/arm/machine-gmon.h: New file, use assembly to avoid
above problem.
1997-07-25 16:24 H.J. Lu <hjl@gnu.ai.mit.edu>
* elf/dl-deps.c (_dl_map_object_deps): Fix a typo.
1997-07-22 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* math/libm-test.c (ccos_test, ccosh_test): Fix sign in some
tests.
1997-07-24 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* sunrpc/clnt_udp.c (clntudp_call): Rename cu_wait from timeout to
not shadow the variable in the outer scope.
