linux-kernel - Re: [PATCH 2/4] lpfc: reduce stack size with CONFIG_GCC_PLUGIN_STRUCTLEAK

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Message-ID: <3027eebb-e49f-6db6-ae0a-39a61c0e34e1@broadcom.com>
Date:   Fri, 28 Jun 2019 11:57:22 -0700
From:   James Smart <james.smart@...adcom.com>
To:     Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     Larry Finger <Larry.Finger@...inger.net>,
        Florian Schilhabel <florian.c.schilhabel@...glemail.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        Wensong Zhang <wensong@...ux-vs.org>,
        Simon Horman <horms@...ge.net.au>,
        Julian Anastasov <ja@....bg>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        James Morris <jmorris@...ei.org>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        netdev@...r.kernel.org, lvs-devel@...r.kernel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Hannes Reinecke <hare@...e.com>, Willy Tarreau <w@....eu>,
        Silvio Cesare <silvio.cesare@...il.com>
Subject: Re: [PATCH 2/4] lpfc: reduce stack size with
 CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE



On 6/28/2019 5:37 AM, Arnd Bergmann wrote:
> The lpfc_debug_dump_all_queues() function repeatedly calls into
> lpfc_debug_dump_qe(), which has a temporary 128 byte buffer.
> This was fine before the introduction of CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE
> because each instance could occupy the same stack slot. However,
> now they each get their own copy, which leads to a huge increase
> in stack usage as seen from the compiler warning:
>
> drivers/scsi/lpfc/lpfc_debugfs.c: In function 'lpfc_debug_dump_all_queues':
> drivers/scsi/lpfc/lpfc_debugfs.c:6474:1: error: the frame size of 1712 bytes is larger than 100 bytes [-Werror=frame-larger-than=]
>
> Avoid this by not marking lpfc_debug_dump_qe() as inline so the
> compiler can choose to emit a static version of this function
> when it's needed or otherwise silently drop it. As an added benefit,
> not inlining multiple copies of this function means we save several
> kilobytes of .text section, reducing the file size from 47kb to 43.
>
> It is somewhat unusual to have a function that is static but not
> inline in a header file, but this does not cause problems here
> because it is only used by other inline functions. It would
> however seem reasonable to move all the lpfc_debug_dump_* functions
> into lpfc_debugfs.c and not mark them inline as a later cleanup.

I agree with this cleanup.

>
> Fixes: 81a56f6dcd20 ("gcc-plugins: structleak: Generalize to all variable types")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/scsi/lpfc/lpfc_debugfs.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
>

Reviewed-by: James Smart <james.smart@...adcom.com>

-- james