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

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Date:   Thu,  3 May 2018 14:50:50 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        "David S . Miller" <davem@...emloft.net>,
        linux-nfs@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH RESEND] SUNRPC: fix include for cmpxchg_relaxed()

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>
-- 
2.11.0