[RFC PATCH for 4.18 00/16] Restartable Sequences

[Mathieu Desnoyers]

Hi,

Here is an updated RFC of the rseq patchset. It only includes rseq.
Further improvements are kept for later.

Compared to the previous version of this series, CONFIG_DEBUG_RSEQ=y now
ensures that system calls are not issued within a rseq critical section,
else the process is killed. This check, performed by rseq_syscall(), has
been wired up and tested on x86 32/64, arm 32, and powerpc 64. It has
only been wired up on powerpc 32 (still needs to be tested).

This enables speeding up the Facebook jemalloc and arm64 PMC read from
user-space use-cases, as well as speedup of use-cases relying on getting
the current cpu number from user-space. We'll have to wait until a more
complete solution is introduced before the LTTng-UST tracer can replace
its ring buffer atomic instructions with rseq though. But let's proceed
one step at a time.

The main change introduced by the removal of cpu_opv from this series
compared to the prior versions of this series in terms of library use
from user-space is that APIs that previously took a CPU number as
argument now only act on the current CPU.

So for instance, this turns:

  int cpu = rseq_per_cpu_lock(lock, target_cpu);
  [...]
  rseq_per_cpu_unlock(lock, cpu);

into

  int cpu = rseq_this_cpu_lock(lock);
  [...]
  rseq_per_cpu_unlock(lock, cpu);

and:

  per_cpu_list_push(list, node, target_cpu);
  [...]
  per_cpu_list_pop(list, node, target_cpu);

into

  this_cpu_list_push(list, node, &cpu);  /* cpu is an output parameter. */
  [...]
  node = this_cpu_list_pop(list, &cpu);  /* cpu is an output parameter. */

Eventually integrating cpu_opv or some alternative will allow passing
the cpu number as parameter rather than requiring the algorithm to work
on the current CPU.

The second effect of not having the cpu_opv fallback is that
line and instruction single-stepping with a debugger transforms rseq
critical sections based on retry loops into never-ending loops.
Debuggers need to use the __rseq_table section to skip those critical
sections in order to correctly behave when single-stepping a thread
which uses rseq in a retry loop. However, applications which use an
alternative fallback method rather than retrying on rseq fast-path abort
won't be affected by this kind of single-stepping issue.

Thanks for your feedback!

Mathieu

Boqun Feng (3):
  powerpc: Add support for restartable sequences
  powerpc: Add syscall detection for restartable sequences
  powerpc: Wire up restartable sequences system call

Mathieu Desnoyers (13):
  uapi headers: Provide types_32_64.h (v2)
  rseq: Introduce restartable sequences system call (v13)
  arm: Add restartable sequences support
  arm: Add syscall detection for restartable sequences
  arm: Wire up restartable sequences system call
  x86: Add support for restartable sequences (v2)
  x86: Wire up restartable sequence system call
  selftests: lib.mk: Introduce OVERRIDE_TARGETS
  rseq: selftests: Provide rseq library (v5)
  rseq: selftests: Provide basic test
  rseq: selftests: Provide basic percpu ops test (v2)
  rseq: selftests: Provide parametrized tests (v2)
  rseq: selftests: Provide Makefile, scripts, gitignore (v2)

 MAINTAINERS                                        |   12 +
 arch/Kconfig                                       |    7 +
 arch/arm/Kconfig                                   |    1 +
 arch/arm/kernel/entry-common.S                     |   25 +-
 arch/arm/kernel/signal.c                           |   14 +
 arch/arm/tools/syscall.tbl                         |    1 +
 arch/powerpc/Kconfig                               |    1 +
 arch/powerpc/include/asm/systbl.h                  |    1 +
 arch/powerpc/include/asm/unistd.h                  |    2 +-
 arch/powerpc/include/uapi/asm/unistd.h             |    1 +
 arch/powerpc/kernel/entry_32.S                     |    7 +
 arch/powerpc/kernel/entry_64.S                     |    8 +
 arch/powerpc/kernel/signal.c                       |    3 +
 arch/x86/Kconfig                                   |    1 +
 arch/x86/entry/common.c                            |    3 +
 arch/x86/entry/syscalls/syscall_32.tbl             |    1 +
 arch/x86/entry/syscalls/syscall_64.tbl             |    1 +
 arch/x86/kernel/signal.c                           |    6 +
 fs/exec.c                                          |    1 +
 include/linux/sched.h                              |  134 +++
 include/linux/syscalls.h                           |    4 +-
 include/trace/events/rseq.h                        |   57 +
 include/uapi/linux/rseq.h                          |  133 +++
 include/uapi/linux/types_32_64.h                   |   50 +
 init/Kconfig                                       |   23 +
 kernel/Makefile                                    |    1 +
 kernel/fork.c                                      |    2 +
 kernel/rseq.c                                      |  357 ++++++
 kernel/sched/core.c                                |    2 +
 kernel/sys_ni.c                                    |    3 +
 tools/testing/selftests/Makefile                   |    1 +
 tools/testing/selftests/lib.mk                     |    4 +
 tools/testing/selftests/rseq/.gitignore            |    6 +
 tools/testing/selftests/rseq/Makefile              |   30 +
 .../testing/selftests/rseq/basic_percpu_ops_test.c |  313 +++++
 tools/testing/selftests/rseq/basic_test.c          |   56 +
 tools/testing/selftests/rseq/param_test.c          | 1260 ++++++++++++++++++++
 tools/testing/selftests/rseq/rseq-arm.h            |  715 +++++++++++
 tools/testing/selftests/rseq/rseq-ppc.h            |  671 +++++++++++
 tools/testing/selftests/rseq/rseq-skip.h           |   65 +
 tools/testing/selftests/rseq/rseq-x86.h            | 1132 ++++++++++++++++++
 tools/testing/selftests/rseq/rseq.c                |  117 ++
 tools/testing/selftests/rseq/rseq.h                |  147 +++
 tools/testing/selftests/rseq/run_param_test.sh     |  121 ++
 44 files changed, 5492 insertions(+), 8 deletions(-)
 create mode 100644 include/trace/events/rseq.h
 create mode 100644 include/uapi/linux/rseq.h
 create mode 100644 include/uapi/linux/types_32_64.h
 create mode 100644 kernel/rseq.c
 create mode 100644 tools/testing/selftests/rseq/.gitignore
 create mode 100644 tools/testing/selftests/rseq/Makefile
 create mode 100644 tools/testing/selftests/rseq/basic_percpu_ops_test.c
 create mode 100644 tools/testing/selftests/rseq/basic_test.c
 create mode 100644 tools/testing/selftests/rseq/param_test.c
 create mode 100644 tools/testing/selftests/rseq/rseq-arm.h
 create mode 100644 tools/testing/selftests/rseq/rseq-ppc.h
 create mode 100644 tools/testing/selftests/rseq/rseq-skip.h
 create mode 100644 tools/testing/selftests/rseq/rseq-x86.h
 create mode 100644 tools/testing/selftests/rseq/rseq.c
 create mode 100644 tools/testing/selftests/rseq/rseq.h
 create mode 100755 tools/testing/selftests/rseq/run_param_test.sh

-- 
2.11.0