git: 85d028223bc2 - main - libthr malloc: support recursion on thr_malloc_umtx.

[Alexander Richardson]

On Tue, 12 Jan 2021 at 10:46, Konstantin Belousov <kib at freebsd.org> wrote:
>
> The branch main has been updated by kib:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=85d028223bc2768651f4d44881644ceb5dc2a664
>
> commit 85d028223bc2768651f4d44881644ceb5dc2a664
> Author:     Konstantin Belousov <kib at FreeBSD.org>
> AuthorDate: 2021-01-12 09:02:37 +0000
> Commit:     Konstantin Belousov <kib at FreeBSD.org>
> CommitDate: 2021-01-12 10:45:44 +0000
>
>     libthr malloc: support recursion on thr_malloc_umtx.
>
>     One possible way the recursion can happen is during fork: suppose
>     that fork is called from early code that did not triggered
>     jemalloc(3) initialization yet. Then we lock thr_malloc lock, and
>     call malloc_prefork() that might require initialization of jemalloc
>     pthread_mutexes, calling into libthr malloc. It is safe to allow
>     recursion for this occurence.
>
>     PR:     252579
>     Reported by:    Vasily Postnicov <shamaz.mazum at gmail.com>
>     MFC after:      1 week
>     Sponsored by:   The FreeBSD Foundation
> ---
>  lib/libthr/thread/thr_malloc.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/lib/libthr/thread/thr_malloc.c b/lib/libthr/thread/thr_malloc.c
> index 2f1c81142942..80a81f9c6c27 100644
> --- a/lib/libthr/thread/thr_malloc.c
> +++ b/lib/libthr/thread/thr_malloc.c
> @@ -41,6 +41,7 @@ int npagesizes;
>  size_t *pagesizes;
>  static size_t pagesizes_d[2];
>  static struct umutex thr_malloc_umtx;
> +static u_int thr_malloc_umtx_level;
>
>  void
>  __thr_malloc_init(void)
> @@ -60,11 +61,16 @@ __thr_malloc_init(void)
>  static void
>  thr_malloc_lock(struct pthread *curthread)
>  {
> +       uint32_t curtid;
>
>         if (curthread == NULL)
>                 return;
>         curthread->locklevel++;
> -       _thr_umutex_lock(&thr_malloc_umtx, TID(curthread));
> +       curtid = TID(curthread);
> +       if ((uint32_t)thr_malloc_umtx.m_owner == curtid)
> +               thr_malloc_umtx_level++;
> +       else
> +               _thr_umutex_lock(&thr_malloc_umtx, curtid);
>  }
>
>  static void
> @@ -73,7 +79,10 @@ thr_malloc_unlock(struct pthread *curthread)
>
>         if (curthread == NULL)
>                 return;
> -       _thr_umutex_unlock(&thr_malloc_umtx, TID(curthread));
> +       if (thr_malloc_umtx_level > 0)
> +               thr_malloc_umtx_level--;

Should this also assert that "thr_malloc_umtx.m_owner == curtid"?

Thanks,
Alex

> +       else
> +               _thr_umutex_unlock(&thr_malloc_umtx, TID(curthread));
>         curthread->locklevel--;
>         _thr_ast(curthread);
>  }