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Re: [PATCH] Document a behavior of an elided pthread_rwlock_unlock
- From: Torvald Riegel <triegel at redhat dot com>
- To: Tulio Magno Quites Machado Filho <tuliom at linux dot vnet dot ibm dot com>
- Cc: libc-alpha at sourceware dot org
- Date: Mon, 24 Oct 2016 19:08:50 +0200
- Subject: Re: [PATCH] Document a behavior of an elided pthread_rwlock_unlock
- Authentication-results: sourceware.org; auth=none
- References: <1477083990-9983-1-git-send-email-tuliom@linux.vnet.ibm.com>
On Fri, 2016-10-21 at 19:06 -0200, Tulio Magno Quites Machado Filho
wrote:
> Explain that pthread_rwlock_unlock may crash if called on a lock not
> held by the current thread.
>
> 2016-10-21 Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>
>
> * nptl/pthread_rwlock_unlock.c: Add a comment explaining its
> behavior when eliding a lock not held by the current thread.
> * sysdeps/powerpc/nptl/elide.h: Likewise.
> ---
> nptl/pthread_rwlock_unlock.c | 4 ++++
> sysdeps/powerpc/nptl/elide.h | 2 ++
> 2 files changed, 6 insertions(+)
>
> diff --git a/nptl/pthread_rwlock_unlock.c b/nptl/pthread_rwlock_unlock.c
> index a6cadd4..112f748 100644
> --- a/nptl/pthread_rwlock_unlock.c
> +++ b/nptl/pthread_rwlock_unlock.c
> @@ -35,6 +35,10 @@ __pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
>
> LIBC_PROBE (rwlock_unlock, 1, rwlock);
>
> + /* Trying to elide an unlocked lock may crash the process. This
> + is expected and is compatible with POSIX.1-2008: "results are
> + undefined if the read-write lock rwlock is not held by the
> + calling thread". */
> if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
> && rwlock->__data.__nr_readers == 0))
> return 0;
> diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
> index 77bd82e..c573981 100644
> --- a/sysdeps/powerpc/nptl/elide.h
> +++ b/sysdeps/powerpc/nptl/elide.h
> @@ -102,6 +102,8 @@ __elide_unlock (int is_lock_free)
> {
> if (is_lock_free)
> {
> + /* Intentionally crashes when trying to unlock a lock not held by this
> + thread. */
I'd rather say that this can happen, and is okay (refering to the
comment in pthread_rwlock_unlock.c). Otherwise, LGTM.
> __libc_tend (0);
> return true;
> }