[PATCH 00/10] nptl: Fix Race conditions in pthread cancellation (BZ#12683)

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

Hi all,

This is an updated version of my previous patchset to fix BZ#12683 [1] and
it superseeds the previous one. The differences from previous version are:

- ARM fixes for syscall-cancel.h generation
- General fixed on syscall cancel mechanism (due ARM fixes)
- More tests to check for failure paths that should set erro
- Rework i386 port to avoid create specific arch libc-cancellation.c. Instead
  extend INLINE_SYSCALL_NCS to accept 6 arguments.
- Add s390 and s390x support (thanks to Stefan Liebler).

The patchset fixes the x86_64, i386, x32, powerpc32, powerpc64{le}, aarch64,
and ARM port and also include the fix for s390 and s390x from Stefan Liebler. 

It will require some help for alpha, hppa, ia64, m68k, microblaze, nios2, sh,
sparc, and tile. I summarized in wiki page [2] the steps required to adjust 
the remaining architectures, but based on arm/aarch64 the minimal adjustments
required are:

1. Write a new syscall implementation at sysdeps/unix/sysv/linux/<arch>/syscall_cancel.S
   that basically do:

long int __syscall_cancel_arch (volatile unsigned int *cancelhandling,
  __syscall_arg_t nr, __syscall_arg_t arg1, __syscall_arg_t arg2, 
  __syscall_arg_t arg3, __syscall_arg_t arg4, __syscall_arg_t arg5,
  __syscall_arg_t arg6)
{
  if (*cancelhandling & CANCELED_BITMASK)
    __syscall_do_cancel()

  return INLINE_SYSCALL (nr, 6, arg1, arg2, arg3, arg4, arg5, arg6);
}

2. Adjust sysdeps/unix/sysv/linux/<arch>/sysdep-cancel.h to make cancellable
   syscalls to call __syscall_cancel instead of *_{enable,disable}_asynccancel.

3. Create a function to get current IP address based on ucontext_t:

static inline
long int __pthread_get_ip (const struct ucontext *uc)
{
  // TODO: return current IP based on uc.
}

4. Define both SYSCALL_CANCEL_ERROR(__val) and SYSCALL_CANCEL_ERRNO(__val)
   macros.

For x86_64 and i386 implementation my approach was to just remove the
pthread_cond_{timed}wait assembly implementation and use default C code, but
since Torvald Riegel new condvar implementation [3] also removed them this
patchset do not contain such removals. Also, this fix is easy to adjust
to new futex API also proposed by Torvalds and I can adjust the patch when
the new API is pushed upstream. The bulk of implementation just depend of a
cancellable futex call done by new mechanism which is orthogonal of the new
proposed futex API.

The idea is try to push it for 2.23 and I have a personal branch [4] with
a working tree for the aforementioned architectures.

[1] https://sourceware.org/ml/libc-alpha/2015-08/msg01286.html
[2] https://sourceware.org/glibc/wiki/Release/2.21/bz12683
[3] https://sourceware.org/ml/libc-alpha/2015-05/msg00287.htm
[4] https://sourceware.org/git/?p=glibc.git;a=shortlog;h=refs/heads/azanella/bz12683