[PATCH] mlx5: avoid frame overflow warning

[PATCH] mlx5: avoid frame overflow warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

Building mlx5 on s390 shows a rather high stack usage that can exceed
the warning limit when that is set to a lower but still reasonable value:

drivers/infiniband/hw/mlx5/wr.c:1051:5: error: stack frame size (1328) exceeds limit (1280) in 'mlx5_ib_post_send' [-Werror,-Wframe-larger-than]

The problem here is 'struct ib_reg_wr' on the stack of
handle_reg_mr_integrity(), which gets inlined into mlx5_ib_post_send()
along with a number of smaller functions.

Keeping the inner function out of line like gcc does avoids the
warning and reduces the total stack usage in other functions called
from mlx5_ib_post_send(), though handle_reg_mr_integrity() itself
still has the same problem as before.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Dynamically allocating ib_reg_wr would be another option, actually
reducing the stack usage but adding a little bit of complexity
from error handling.
---
 drivers/infiniband/hw/mlx5/wr.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/wr.c b/drivers/infiniband/hw/mlx5/wr.c
index 9947feb7fb8a..fca9e1d9d5e9 100644
--- a/drivers/infiniband/hw/mlx5/wr.c
+++ b/drivers/infiniband/hw/mlx5/wr.c
@@ -840,13 +840,15 @@ static int handle_psv(struct mlx5_ib_dev *dev, struct mlx5_ib_qp *qp,
 	return err;
 }
 
-static int handle_reg_mr_integrity(struct mlx5_ib_dev *dev,
-				   struct mlx5_ib_qp *qp,
-				   const struct ib_send_wr *wr,
-				   struct mlx5_wqe_ctrl_seg **ctrl, void **seg,
-				   int *size, void **cur_edge,
-				   unsigned int *idx, int nreq, u8 fence,
-				   u8 next_fence)
+static noinline_for_stack int handle_reg_mr_integrity(struct mlx5_ib_dev *dev,
+						      struct mlx5_ib_qp *qp,
+						      const struct ib_send_wr *wr,
+						      struct mlx5_wqe_ctrl_seg **ctrl,
+						      void **seg,
+						      int *size, void **cur_edge,
+						      unsigned int *idx, int nreq,
+						      u8 fence,
+						      u8 next_fence)
 {
 	struct mlx5_ib_mr *mr;
 	struct mlx5_ib_mr *pi_mr;
-- 
2.39.5