[Mesa-dev] [PATCH] RFC: Workaround for pthread_setaffinity_np() seccomp filtering

[Marek Olšák]

I'd rather have something more robust than an env var, like catching SIGSYS.

Marek

On Wed, Feb 27, 2019 at 6:13 PM <marcandre.lureau at redhat.com> wrote:

> From: Marc-André Lureau <marcandre.lureau at redhat.com>
>
> Since commit d877451b48a59ab0f9a4210fc736f51da5851c9a ("util/u_queue:
> add UTIL_QUEUE_INIT_SET_FULL_THREAD_AFFINITY"), mesa calls
> sched_setaffinity syscall. Unfortunately, qemu crashes with SIGSYS
> when sandboxing is enabled (by default with libvirt), as this syscall
> is filtered.
>
> There doesn't seem to be a way to check for the seccomp rule other
> than doing a call, which may result in various behaviour depending on
> seccomp actions. There is a PTRACE_SECCOMP_GET_FILTER, but it is
> low-level and a priviledged operation (but there might be a way to use
> it?). A safe way would be to try the call in a subprocess,
> unfortunately, qemu also prohibits fork(). Also this could be subject
> to TOCTOU.
>
> There seems to be few solutions, but the issue can be considered a
> regression for various libvirt/Boxes users.
>
> Introduce MESA_NO_THREAD_AFFINITY environment variable to prevent the
> offending call. Wrap pthread_setaffinity_np() in a utility function
> u_pthread_setaffinity_np(), returning a EACCESS error if the variable
> is set.
>
> Note: one call is left with a FIXME, as I didn't investigate how to
> build and test it, help welcome!
>
> See also:
> https://bugs.freedesktop.org/show_bug.cgi?id=109695
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau at redhat.com>
> ---
>  .../drivers/swr/rasterizer/core/threads.cpp       |  1 +
>  src/util/u_queue.c                                |  2 +-
>  src/util/u_thread.h                               | 15 ++++++++++++++-
>  3 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/src/gallium/drivers/swr/rasterizer/core/threads.cpp
> b/src/gallium/drivers/swr/rasterizer/core/threads.cpp
> index e30c1170568..d10c79512a1 100644
> --- a/src/gallium/drivers/swr/rasterizer/core/threads.cpp
> +++ b/src/gallium/drivers/swr/rasterizer/core/threads.cpp
> @@ -364,6 +364,7 @@ void bindThread(SWR_CONTEXT* pContext,
>      CPU_ZERO(&cpuset);
>      CPU_SET(threadId, &cpuset);
>
> +    /* FIXME: use u_pthread_setaffinity_np() if possible */
>      int err = pthread_setaffinity_np(thread, sizeof(cpu_set_t), &cpuset);
>      if (err != 0)
>      {
> diff --git a/src/util/u_queue.c b/src/util/u_queue.c
> index 3812c824b6d..dea8d2bb4ae 100644
> --- a/src/util/u_queue.c
> +++ b/src/util/u_queue.c
> @@ -249,7 +249,7 @@ util_queue_thread_func(void *input)
>        for (unsigned i = 0; i < CPU_SETSIZE; i++)
>           CPU_SET(i, &cpuset);
>
> -      pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);
> +      u_pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);
>     }
>  #endif
>
> diff --git a/src/util/u_thread.h b/src/util/u_thread.h
> index a46c18d3db2..a4e6dbae5d7 100644
> --- a/src/util/u_thread.h
> +++ b/src/util/u_thread.h
> @@ -70,6 +70,19 @@ static inline void u_thread_setname( const char *name )
>     (void)name;
>  }
>
> +#if defined(HAVE_PTHREAD_SETAFFINITY)
> +static inline int u_pthread_setaffinity_np(pthread_t thread, size_t
> cpusetsize,
> +                                           const cpu_set_t *cpuset)
> +{
> +   if (getenv("MESA_NO_THREAD_AFFINITY")) {
> +      errno = EACCES;
> +      return -1;
> +   }
> +
> +   return pthread_setaffinity_np(thread, cpusetsize, cpuset);
> +}
> +#endif
> +
>  /**
>   * An AMD Zen CPU consists of multiple modules where each module has its
> own L3
>   * cache. Inter-thread communication such as locks and atomics between
> modules
> @@ -89,7 +102,7 @@ util_pin_thread_to_L3(thrd_t thread, unsigned L3_index,
> unsigned cores_per_L3)
>     CPU_ZERO(&cpuset);
>     for (unsigned i = 0; i < cores_per_L3; i++)
>        CPU_SET(L3_index * cores_per_L3 + i, &cpuset);
> -   pthread_setaffinity_np(thread, sizeof(cpuset), &cpuset);
> +   u_pthread_setaffinity_np(thread, sizeof(cpuset), &cpuset);
>  #endif
>  }
>
> --
> 2.21.0
>
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> mesa-dev mailing list
> mesa-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
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