Re: [PATCH net-next] devlink: Fix excessive stack usage in rate TC bandwidth parsing

[Jiri Pirko]

Tue, Jul 22, 2025 at 11:13:29AM +0200, tariqt@xxxxxxxxxx wrote:
>From: Carolina Jubran <cjubran@xxxxxxxxxx>
>
>The devlink_nl_rate_tc_bw_parse function uses a large stack array for
>devlink attributes, which triggers a warning about excessive stack
>usage:
>
>net/devlink/rate.c: In function 'devlink_nl_rate_tc_bw_parse':
>net/devlink/rate.c:382:1: error: the frame size of 1648 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]
>
>Introduce a separate attribute set specifically for rate TC bandwidth
>parsing that only contains the two attributes actually used: index
>and bandwidth. This reduces the stack array from DEVLINK_ATTR_MAX
>entries to just 2 entries, solving the stack usage issue.
>
>Update devlink selftest to use the new 'index' and 'bw' attribute names
>consistent with the YAML spec.
>
>Example usage with ynl with the new spec:
>
>    ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/devlink.yaml \
>      --do rate-set --json '{
>      "bus-name": "pci",
>      "dev-name": "0000:08:00.0",
>      "port-index": 1,
>      "rate-tc-bws": [
>        {"index": 0, "bw": 50},
>        {"index": 1, "bw": 50},
>        {"index": 2, "bw": 0},
>        {"index": 3, "bw": 0},
>        {"index": 4, "bw": 0},
>        {"index": 5, "bw": 0},
>        {"index": 6, "bw": 0},
>        {"index": 7, "bw": 0}
>      ]
>    }'
>
>    ./tools/net/ynl/cli.py --spec Documentation/netlink/specs/devlink.yaml \
>      --do rate-get --json '{
>      "bus-name": "pci",
>      "dev-name": "0000:08:00.0",
>      "port-index": 1
>    }'
>
>    output for rate-get:
>    {'bus-name': 'pci',
>     'dev-name': '0000:08:00.0',
>     'port-index': 1,
>     'rate-tc-bws': [{'bw': 50, 'index': 0},
>                     {'bw': 50, 'index': 1},
>                     {'bw': 0, 'index': 2},
>                     {'bw': 0, 'index': 3},
>                     {'bw': 0, 'index': 4},
>                     {'bw': 0, 'index': 5},
>                     {'bw': 0, 'index': 6},
>                     {'bw': 0, 'index': 7}],
>     'rate-tx-max': 0,
>     'rate-tx-priority': 0,
>     'rate-tx-share': 0,
>     'rate-tx-weight': 0,
>     'rate-type': 'leaf'}
>
>Fixes: 566e8f108fc7 ("devlink: Extend devlink rate API with traffic classes bandwidth management")
>Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
>Closes: https://lore.kernel.org/netdev/20250708160652.1810573-1-arnd@xxxxxxxxxx/
>Reported-by: kernel test robot <lkp@xxxxxxxxx>
>Closes: https://lore.kernel.org/oe-kbuild-all/202507171943.W7DJcs6Y-lkp@xxxxxxxxx/
>Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
>Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
>Signed-off-by: Carolina Jubran <cjubran@xxxxxxxxxx>
>Tested-by: Carolina Jubran <cjubran@xxxxxxxxxx>
>Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>

Reviewed-by: Jiri Pirko <jiri@xxxxxxxxxx>