linux-kernel - Re: [PATCH glibc 2/3] glibc: sched_getcpu(): use rseq cpu

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Message-ID: <87imgqdib5.fsf@oldenburg2.str.redhat.com>
Date:   Wed, 20 May 2020 12:14:38 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Mathieu Desnoyers via Libc-alpha <libc-alpha@...rceware.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        linux-api@...r.kernel.org, Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ben Maurer <bmaurer@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Paul Turner <pjt@...gle.com>,
        Joseph Myers <joseph@...esourcery.com>
Subject: Re: [PATCH glibc 2/3] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux (v7)

* Mathieu Desnoyers via Libc-alpha:

> diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
> index c019cfb3cf..2269c4f2bd 100644
> --- a/sysdeps/unix/sysv/linux/sched_getcpu.c
> +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
> @@ -18,10 +18,15 @@
>  #include <errno.h>
>  #include <sched.h>
>  #include <sysdep.h>
> +#include <atomic.h>
>  #include <sysdep-vdso.h>
>  
> -int
> -sched_getcpu (void)
> +#ifdef HAVE_GETCPU_VSYSCALL
> +# define HAVE_VSYSCALL
> +#endif

I think the #ifdef is a result of an incorrect merge of commit
d0def09ff6bbf1537beec305fdfe96a21174fb31 ("linux: Fix vDSO macros build
with time64 interfaces") and it should be removed.

The commit subject should probably say “Linux: Use rseq in sched_getcpu
if available”.

Thanks,
Florian