linux-kernel - Re: [PATCH] SUNRPC: use cmpxchg64() in gss_seq_send64_fetch_and

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Date:   Fri, 5 Oct 2018 13:36:19 +0000
From:   Trond Myklebust <trondmy@...merspace.com>
To:     "arnd@...db.de" <arnd@...db.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jlayton@...nel.org" <jlayton@...nel.org>,
        "bfields@...ldses.org" <bfields@...ldses.org>,
        "linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
        "james@...le.org.uk" <james@...le.org.uk>,
        "anna.schumaker@...app.com" <anna.schumaker@...app.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: Re: [PATCH] SUNRPC: use cmpxchg64() in gss_seq_send64_fetch_and_inc()

On Tue, 2018-10-02 at 22:57 +0200, Arnd Bergmann wrote:
> The newly introduced gss_seq_send64_fetch_and_inc() fails to build on
> 32-bit architectures:
> 
> net/sunrpc/auth_gss/gss_krb5_seal.c:144:14: note: in expansion of
> macro 'cmpxchg'
>    seq_send = cmpxchg(&ctx->seq_send64, old, old + 1);
>               ^~~~~~~
> arch/x86/include/asm/cmpxchg.h:128:3: error: call to
> '__cmpxchg_wrong_size' declared with attribute error: Bad argument
> size for cmpxchg
>    __cmpxchg_wrong_size();     \
> 
> As the message tells us, cmpxchg() cannot be used on 64-bit
> arguments,
> that's what cmpxchg64() does.
> 
> Fixes: 571ed1fd2390 ("SUNRPC: Replace krb5_seq_lock with a lockless
> scheme")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  net/sunrpc/auth_gss/gss_krb5_seal.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sunrpc/auth_gss/gss_krb5_seal.c
> b/net/sunrpc/auth_gss/gss_krb5_seal.c
> index 92594681d619..5775b9805bdc 100644
> --- a/net/sunrpc/auth_gss/gss_krb5_seal.c
> +++ b/net/sunrpc/auth_gss/gss_krb5_seal.c
> @@ -141,7 +141,7 @@ gss_seq_send64_fetch_and_inc(struct krb5_ctx
> *ctx)
>  
>  	do {
>  		old = seq_send;
> -		seq_send = cmpxchg(&ctx->seq_send64, old, old + 1);
> +		seq_send = cmpxchg64(&ctx->seq_send64, old, old + 1);
>  	} while (old != seq_send);
>  	return seq_send;
>  }

Thanks Arndt! Applied.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@...merspace.com