linux-kernel - [PATCH] IB/verbs: avoid nested container

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Date:   Mon, 26 Oct 2020 17:15:39 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Doug Ledford <dledford@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Shamir Rabinovitch <shamir.rabinovitch@...cle.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Jason Gunthorpe <jgg@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Michael Guralnik <michaelgur@...lanox.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] IB/verbs: avoid nested container_of()

From: Arnd Bergmann <arnd@...db.de>

Nested container_of() calls work correctly but cause a warning when
building with W=2. Invoking it from an inline function like in
drivers/infiniband/hw/mlx5/mlx5_ib.h means we get hundreds of
warnings like:

include/linux/kernel.h:852:8: warning: declaration of '__mptr' shadows a previous local [-Wshadow]
  852 |  void *__mptr = (void *)(ptr);     \
      |        ^~~~~~
include/rdma/uverbs_ioctl.h:651:11: note: in expansion of macro 'container_of'
  651 |  (udata ? container_of(container_of(udata, struct uverbs_attr_bundle,   \
      |           ^~~~~~~~~~~~
include/rdma/uverbs_ioctl.h:651:24: note: in expansion of macro 'container_of'
  651 |  (udata ? container_of(container_of(udata, struct uverbs_attr_bundle,   \
      |                        ^~~~~~~~~~~~
drivers/infiniband/hw/mthca/mthca_qp.c:564:35: note: in expansion of macro 'rdma_udata_to_drv_context'
  564 |  struct mthca_ucontext *context = rdma_udata_to_drv_context(
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/kernel.h:852:8: note: shadowed declaration is here
  852 |  void *__mptr = (void *)(ptr);     \
      |        ^~~~~~
include/rdma/uverbs_ioctl.h:651:11: note: in expansion of macro 'container_of'
  651 |  (udata ? container_of(container_of(udata, struct uverbs_attr_bundle,   \
      |           ^~~~~~~~~~~~
drivers/infiniband/hw/mthca/mthca_qp.c:564:35: note: in expansion of macro 'rdma_udata_to_drv_context'
  564 |  struct mthca_ucontext *context = rdma_udata_to_drv_context(
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~
In file included from <command-line>:
include/linux/kernel.h:852:8: warning: declaration of '__mptr' shadows a previous local [-Wshadow]
  852 |  void *__mptr = (void *)(ptr);     \
      |        ^~~~~~

Rewrite the macro to use an inline function internally, which makes
it more readable and reduces the amount of useless output from
make W=2.

Fixes: 730623f4a56f ("IB/verbs: Add helper function rdma_udata_to_drv_context")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 include/rdma/uverbs_ioctl.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/include/rdma/uverbs_ioctl.h b/include/rdma/uverbs_ioctl.h
index b00270c72740..bf167ef6c688 100644
--- a/include/rdma/uverbs_ioctl.h
+++ b/include/rdma/uverbs_ioctl.h
@@ -647,12 +647,15 @@ static inline bool uverbs_attr_is_valid(const struct uverbs_attr_bundle *attrs_b
  * 'ucontext'.
  *
  */
-#define rdma_udata_to_drv_context(udata, drv_dev_struct, member)               \
-	(udata ? container_of(container_of(udata, struct uverbs_attr_bundle,   \
-					   driver_udata)                       \
-				      ->context,                               \
-			      drv_dev_struct, member) :                        \
-		 (drv_dev_struct *)NULL)
+static inline struct uverbs_attr_bundle *
+rdma_udata_to_uverbs_attr_bundle(struct ib_udata *udata)
+{
+	return container_of(udata, struct uverbs_attr_bundle, driver_udata);
+}
+
+#define rdma_udata_to_drv_context(udata, drv_dev_struct, member)                \
+	(udata ? container_of(rdma_udata_to_uverbs_attr_bundle(udata)->context, \
+			      drv_dev_struct, member) : (drv_dev_struct *)NULL)
 
 #define IS_UVERBS_COPY_ERR(_ret)		((_ret) && (_ret) != -ENOENT)
 
-- 
2.27.0