linux-kernel - [PATCH] net/mlx5: reduce stack usage in FW tracer

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Date:   Fri,  6 Sep 2019 17:11:16 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Arnd Bergmann <arnd@...db.de>, Feras Daoud <ferasda@...lanox.com>,
        Erez Shitrit <erezsh@...lanox.com>,
        Moshe Shemesh <moshe@...lanox.com>,
        Eran Ben Elisha <eranbe@...lanox.com>, Qian Cai <cai@....pw>,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] net/mlx5: reduce stack usage in FW tracer

It's generally not ok to put a 512 byte buffer on the stack, as kernel
stack is a scarce resource:

drivers/net/ethernet/mellanox/mlx5/core/diag/fw_tracer.c:660:13: error: stack frame size of 1032 bytes in function 'mlx5_fw_tracer_handle_traces' [-Werror,-Wframe-larger-than=]

This is done in a context that is allowed to sleep, so using
dynamic allocation is ok as well. I'm not too worried about
runtime overhead, as this already contains an snprintf() and
other expensive functions.

Fixes: 70dd6fdb8987 ("net/mlx5: FW tracer, parse traces and kernel tracing support")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 .../mellanox/mlx5/core/diag/fw_tracer.c       | 21 ++++++++++---------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/diag/fw_tracer.c b/drivers/net/ethernet/mellanox/mlx5/core/diag/fw_tracer.c
index 2011eaf15cc5..d81e78060f9f 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/diag/fw_tracer.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/diag/fw_tracer.c
@@ -557,16 +557,16 @@ static void mlx5_tracer_print_trace(struct tracer_string_format *str_frmt,
 				    struct mlx5_core_dev *dev,
 				    u64 trace_timestamp)
 {
-	char	tmp[512];
-
-	snprintf(tmp, sizeof(tmp), str_frmt->string,
-		 str_frmt->params[0],
-		 str_frmt->params[1],
-		 str_frmt->params[2],
-		 str_frmt->params[3],
-		 str_frmt->params[4],
-		 str_frmt->params[5],
-		 str_frmt->params[6]);
+	char *tmp = kasprintf(GFP_KERNEL, str_frmt->string,
+			      str_frmt->params[0],
+			      str_frmt->params[1],
+			      str_frmt->params[2],
+			      str_frmt->params[3],
+			      str_frmt->params[4],
+			      str_frmt->params[5],
+			      str_frmt->params[6]);
+	if (!tmp)
+		return;
 
 	trace_mlx5_fw(dev->tracer, trace_timestamp, str_frmt->lost,
 		      str_frmt->event_id, tmp);
@@ -576,6 +576,7 @@ static void mlx5_tracer_print_trace(struct tracer_string_format *str_frmt,
 
 	/* remove it from hash */
 	mlx5_tracer_clean_message(str_frmt);
+	kfree(tmp);
 }
 
 static int mlx5_tracer_handle_string_trace(struct mlx5_fw_tracer *tracer,
-- 
2.20.0