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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Arnd Bergmann <arnd@arndb.de>,
        "David S . Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>, netdev@vger.kernel.org,
        clang-built-linux@googlegroups.com
Subject: [PATCH AUTOSEL 5.2 167/171] cxgb4: reduce kernel stack usage in cudbg_collect_mem_region()
Date:   Thu, 18 Jul 2019 23:56:38 -0400
Message-Id: <20190719035643.14300-167-sashal@kernel.org>
In-Reply-To: <20190719035643.14300-1-sashal@kernel.org>
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From: Arnd Bergmann <arnd@arndb.de>

[ Upstream commit 752c2ea2d8e7c23b0f64e2e7d4337f3604d44c9f ]

The cudbg_collect_mem_region() and cudbg_read_fw_mem() both use several
hundred kilobytes of kernel stack space. One gets inlined into the other,
which causes the stack usage to be combined beyond the warning limit
when building with clang:

drivers/net/ethernet/chelsio/cxgb4/cudbg_lib.c:1057:12: error: stack frame size of 1244 bytes in function 'cudbg_collect_mem_region' [-Werror,-Wframe-larger-than=]

Restructuring cudbg_collect_mem_region() lets clang do the same
optimization that gcc does and reuse the stack slots as it can
see that the large variables are never used together.

A better fix might be to avoid using cudbg_meminfo on the stack
altogether, but that requires a larger rewrite.

Fixes: a1c69520f785 ("cxgb4: collect MC memory dump")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../net/ethernet/chelsio/cxgb4/cudbg_lib.c    | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/cudbg_lib.c b/drivers/net/ethernet/chelsio/cxgb4/cudbg_lib.c
index a76529a7662d..c2e92786608b 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cudbg_lib.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cudbg_lib.c
@@ -1054,14 +1054,12 @@ static void cudbg_t4_fwcache(struct cudbg_init *pdbg_init,
 	}
 }
 
-static int cudbg_collect_mem_region(struct cudbg_init *pdbg_init,
-				    struct cudbg_buffer *dbg_buff,
-				    struct cudbg_error *cudbg_err,
-				    u8 mem_type)
+static unsigned long cudbg_mem_region_size(struct cudbg_init *pdbg_init,
+					   struct cudbg_error *cudbg_err,
+					   u8 mem_type)
 {
 	struct adapter *padap = pdbg_init->adap;
 	struct cudbg_meminfo mem_info;
-	unsigned long size;
 	u8 mc_idx;
 	int rc;
 
@@ -1075,7 +1073,16 @@ static int cudbg_collect_mem_region(struct cudbg_init *pdbg_init,
 	if (rc)
 		return rc;
 
-	size = mem_info.avail[mc_idx].limit - mem_info.avail[mc_idx].base;
+	return mem_info.avail[mc_idx].limit - mem_info.avail[mc_idx].base;
+}
+
+static int cudbg_collect_mem_region(struct cudbg_init *pdbg_init,
+				    struct cudbg_buffer *dbg_buff,
+				    struct cudbg_error *cudbg_err,
+				    u8 mem_type)
+{
+	unsigned long size = cudbg_mem_region_size(pdbg_init, cudbg_err, mem_type);
+
 	return cudbg_read_fw_mem(pdbg_init, dbg_buff, mem_type, size,
 				 cudbg_err);
 }
-- 
2.20.1