netdev - Re: [PATCH] [net-next] cxgb4: reduce kernel stack usage in cudbg_collect_mem

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Message-Id: <20190712.153632.1007215196498198399.davem@davemloft.net>
Date:   Fri, 12 Jul 2019 15:36:32 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     arnd@...db.de
Cc:     vishal@...lsio.com, rahul.lakkireddy@...lsio.com,
        ganeshgr@...lsio.com, alexios.zavras@...el.com, arjun@...lsio.com,
        surendra@...lsio.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] [net-next] cxgb4: reduce kernel stack usage in
 cudbg_collect_mem_region()

From: Arnd Bergmann <arnd@...db.de>
Date: Fri, 12 Jul 2019 11:06:33 +0200

> 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@...db.de>

Applied.