On Thu, Mar 07, 2019 at 04:58:35PM +0100, Arnd Bergmann wrote:
> clang inlines the dev_ethtool() more aggressively than gcc does, leading
> to a larger amount of used stack space:
>
> net/core/ethtool.c:2536:24: error: stack frame size of 1216 bytes in function
> 'dev_ethtool' [-Werror,-Wframe-larger-than=]
>
> Marking the sub-functions that require the most stack space as
> noinline_for_stack gives us reasonable behavior on all compilers.
>
> Signed-off-by: Arnd Bergmann <a...@arndb.de>
> ---
> v2: don't annotate dev_ethtool itself, as pointed out by Michal Kubecek
> ---
> net/core/ethtool.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
Reviewed-by: Michal Kubecek <mkube...@suse.cz>
In the long term, these three functions would IMHO deserve some rework.
While marking them as noinline_for_stack prevents one big stack frame in
dev_ethtool(), we still allocate rather big structures on the stack,
only it won't be in one stack frame. When we take the
dev_ethtool
ethtool_set_perqueue
ethtool_[gs]et_per_queue_coalesce
path, there will still be two 512-byte arrays on the stack, one inside
struct ethtool_per_queue_op in ethtool_set_per_queue() and one as the
queue_mask bitmap in ethtool_[gs]et_per_queue_coalesce() (MAX_NUM_QUEUE
is 4096 now). In other words, actual stack consumption might be
approximately the same after this change as it was before, only divided
into three stack frames.
Michal Kubecek
> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> index d4918ffddda8..b1eb32419732 100644
> --- a/net/core/ethtool.c
> +++ b/net/core/ethtool.c
> @@ -2319,9 +2319,10 @@ static int ethtool_set_tunable(struct net_device *dev,
> void __user *useraddr)
> return ret;
> }
>
> -static int ethtool_get_per_queue_coalesce(struct net_device *dev,
> - void __user *useraddr,
> - struct ethtool_per_queue_op
> *per_queue_opt)
> +static noinline_for_stack int
> +ethtool_get_per_queue_coalesce(struct net_device *dev,
> + void __user *useraddr,
> + struct ethtool_per_queue_op *per_queue_opt)
> {
> u32 bit;
> int ret;
> @@ -2349,9 +2350,10 @@ static int ethtool_get_per_queue_coalesce(struct
> net_device *dev,
> return 0;
> }
>
> -static int ethtool_set_per_queue_coalesce(struct net_device *dev,
> - void __user *useraddr,
> - struct ethtool_per_queue_op
> *per_queue_opt)
> +static noinline_for_stack int
> +ethtool_set_per_queue_coalesce(struct net_device *dev,
> + void __user *useraddr,
> + struct ethtool_per_queue_op *per_queue_opt)
> {
> u32 bit;
> int i, ret = 0;
> @@ -2405,7 +2407,7 @@ static int ethtool_set_per_queue_coalesce(struct
> net_device *dev,
> return ret;
> }
>
> -static int ethtool_set_per_queue(struct net_device *dev,
> +static int noinline_for_stack ethtool_set_per_queue(struct net_device *dev,
> void __user *useraddr, u32 sub_cmd)
> {
> struct ethtool_per_queue_op per_queue_opt;
