linux-kernel - Re: [RFC PATCH for 4.15 14/14] Restartable sequences: Provide self-tests

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Date:   Mon, 16 Oct 2017 14:00:33 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>,
        Josh Triplett <josh@...htriplett.org>,
        Will Deacon <will.deacon@....com>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Russell King <linux@....linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [RFC PATCH for 4.15 14/14] Restartable sequences: Provide self-tests

Mathieu Desnoyers <mathieu.desnoyers@...icios.com> writes:

> Implements two basic tests of RSEQ functionality, and one more
> exhaustive parameterizable test.
>
> The first, "basic_test" only asserts that RSEQ works moderately
> correctly.
> E.g. that:
> - The CPUID pointer works
> - Code infinitely looping within a critical section will eventually be
>   interrupted.
> - Critical sections are interrupted by signals.
>
> "basic_percpu_ops_test" is a slightly more "realistic" variant,
> implementing a few simple per-cpu operations and testing their
> correctness.
>
> "param_test" is a parametrizable restartable sequences test. See
> the "--help" output for usage.
>
> As part of those tests, a helper library "rseq" implements a user-space
> API around restartable sequences. It uses the cpu_opv system call as
> fallback when single-stepped by a debugger. It exposes the instruction
> pointer addresses where the rseq assembly blocks begin and end, as well
> as the associated abort instruction pointer, in the __rseq_table
> section. This section allows debuggers may know where to place
> breakpoints when single-stepping through assembly blocks which may be
> aborted at any point by the kernel.
>
> The following rseq APIs are implemented in this helper library:
> - rseq_register_current_thread()/rseq_unregister_current_thread():
>     register/unregister current thread's use of rseq,
> - rseq_current_cpu_raw():
>     current CPU number,
> - rseq_start():
>     beginning of a restartable sequence,
> - rseq_cpu_at_start():
>     CPU number at start of restartable sequence,
> - rseq_finish():
>     End of restartable sequence made of zero or more loads, completed by
>     a word-sized store,
> - rseq_finish2():
>     End of restartable sequence made of zero or more loads, one
>     speculative word-sized store, completed by a word-sized store,
> - rseq_finish2_release():
>     End of restartable sequence made of zero or more loads, one
>     speculative word-sized store, completed by a word-sized store with
>     release semantic,
> - rseq_finish_memcpy():
>     End of restartable sequence made of zero or more loads, a
>     speculative copy of a variable length memory region, completed by a
>     word-sized store.
> - rseq_finish_memcpy_release():
>     End of restartable sequence made of zero or more loads, a
>     speculative copy of a variable length memory region, completed by a
>     word-sized store with release semantic.
>
> PowerPC tests have been implemented by Boqun Feng.

Hi Boqun,

I'm having trouble testing these, I get:

  ~/linus/tools/testing/selftests/cpu-opv$ ./basic_cpu_opv_test
  Testing test_compare_eq same
  Testing test_compare_eq different
  Testing test_compare_ne same
  Testing test_compare_ne different
  Testing test_2compare_eq index
  Testing test_2compare_ne index
  Testing test_memcpy
  Testing test_memcpy_u32
  Testing test_add
  Testing test_two_add
  Testing test_or
  Testing test_and
  Testing test_xor
  Testing test_lshift
  Testing test_rshift
  Testing test_cmpxchg success
  Testing test_cmpxchg fail
  
  ~/linus/tools/testing/selftests/rseq$ ./basic_test
  testing current cpu
  testing critical section
  testing critical section is interrupted by signal

  ~/linus/tools/testing/selftests/rseq$ ./basic_percpu_ops_test
  ./basic_percpu_ops_test: error while loading shared libraries: R_PPC64_ADDR16_HI re10d8f10a0 for symbol `' out of range
  ~/linus/tools/testing/selftests/rseq$ ./param_test
  ./param_test: error while loading shared libraries: R_PPC64_ADDR16_HI re136251b48 for symbol `' out of range


Any idea what's going on with the last two? I assume you don't see that
in your test setup :)

cheers