netdev - Re: [PATCH RESEND] SUNRPC: fix include for cmpxchg

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Message-ID: <71ed4a99241a6478b91246f967b9e1bc3d68fa9f.camel@kernel.org>
Date:   Thu, 03 May 2018 10:16:49 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Mark Rutland <mark.rutland@....com>, linux-kernel@...r.kernel.org
Cc:     Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        "David S . Miller" <davem@...emloft.net>,
        linux-nfs@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH RESEND] SUNRPC: fix include for cmpxchg_relaxed()

On Thu, 2018-05-03 at 14:50 +0100, Mark Rutland wrote:
> Currently net/sunrpc/xprtmultipath.c is the only file outside of arch/
> headers and asm-generic/ headers to include <asm/cmpxhcg.h>, apparently
> for the use of cmpxchg_relaxed().
> 
> However, many architectures do not provide cmpxchg_relaxed() in their
> <asm/cmpxhcg.h>, and it is necessary to include <linux/atomic.h> to get
> this definition, as noted in Documentation/core-api/atomic_ops.rst:
> 
>   If someone wants to use xchg(), cmpxchg() and their variants,
>   linux/atomic.h should be included rather than asm/cmpxchg.h, unless
>   the code is in arch/* and can take care of itself.
> 
> Evidently we're getting the right header this via some transitive
> include today, but this isn't something we can/should rely upon,
> especially with ongoing rework of the atomic headers for KASAN
> instrumentation.
> 
> Let's fix the code to include <linux/atomic.h>, avoiding fragility.
> 
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Trond Myklebust <trond.myklebust@...marydata.com>
> Cc: Anna Schumaker <anna.schumaker@...app.com>
> Cc: J. Bruce Fields <bfields@...ldses.org>
> Cc: Jeff Layton <jlayton@...chiereds.net>
> Cc: David S. Miller <davem@...emloft.net>
> Cc: linux-nfs@...r.kernel.org
> Cc: netdev@...r.kernel.org
> ---
>  net/sunrpc/xprtmultipath.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> I sent this about a year ago [1], but got no response. This still applies atop
> of v4.17-rc3.
> 
> I'm currently trying to implement instrumented atomics for arm64, and it would
> be great to have this fixed.
> 
> Mark.
> 
> [1] https://lkml.kernel.org/r/1489574142-20856-1-git-send-email-mark.rutland@arm.com
> 
> diff --git a/net/sunrpc/xprtmultipath.c b/net/sunrpc/xprtmultipath.c
> index e2d64c7138c3..d897f41be244 100644
> --- a/net/sunrpc/xprtmultipath.c
> +++ b/net/sunrpc/xprtmultipath.c
> @@ -13,7 +13,7 @@
>  #include <linux/rcupdate.h>
>  #include <linux/rculist.h>
>  #include <linux/slab.h>
> -#include <asm/cmpxchg.h>
> +#include <linux/atomic.h>
>  #include <linux/spinlock.h>
>  #include <linux/sunrpc/xprt.h>
>  #include <linux/sunrpc/addr.h>

Looks fine.

Reviewed-by: Jeff Layton <jlayton@...nel.org>