Re: [PATCH net-next v2 2/3] tcp_hybla: fix divide by zero on rtt0 == 0

[netdev-bot+sashiko]

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Low priority / nit picks for your consideration:

- [Low] In net/ipv4/tcp_hybla.c, the patch replaces `module_param(rtt0,
  int, 0644)` with `module_param_cb(rtt0, &rtt0_ops, &rtt0, 0644)`.

--

tcp_hybla: fix divide by zero on rtt0 == 0

This commit changes the rtt0 module parameter from int to unsigned int.
It also registers rtt0 through module_param_cb() with a setter that only
accepts values from 1 to U32_MAX / USEC_PER_MSEC. That stops
hybla_recalc_param() from dividing by zero, and stops rtt0 * USEC_PER_MSEC
from wrapping on 32-bit.

> diff --git a/net/ipv4/tcp_hybla.c b/net/ipv4/tcp_hybla.c
> index abd7d91807e54..b9b482180d30b 100644
> --- a/net/ipv4/tcp_hybla.c
> +++ b/net/ipv4/tcp_hybla.c
> @@ -26,8 +26,20 @@ struct hybla {

[ ... ]

> +static const struct kernel_param_ops rtt0_ops = {
> +	.set = rtt0_set,
> +	.get = param_get_uint,
> +};
> +
> +module_param_cb(rtt0, &rtt0_ops, &rtt0, 0644);
>  MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)");

[Severity: Low]
Does this drop the parmtype entry for rtt0 from the .modinfo section of
tcp_hybla.ko?

The old module_param() line expanded to module_param_named(), which emits
the type tag:

include/linux/moduleparam.h:
#define module_param_named(name, value, type, perm)			   \
	param_check_##type(name, &(value));				   \
	module_param_cb(name, &param_ops_##type, &value, perm);		   \
	__MODULE_PARM_TYPE(name, #type)

module_param_cb() only expands to __module_param_call():

#define module_param_cb(name, ops, arg, perm)				      \
	__module_param_call(MODULE_PARAM_PREFIX, name, ops, arg, perm, -1, 0)

MODULE_PARM_DESC(rtt0, ...) is still there, but nothing provides a type.
After this change, modinfo tcp_hybla would show a description for rtt0
with no type suffix.

Since the storage is now unsigned int and it is read back with
param_get_uint, could a line like this be added after module_param_cb()?

__MODULE_PARM_TYPE(rtt0, "uint");

Other module_param_cb() users already do this, for example
arch/x86/kvm/mmu/mmu.c, fs/fuse/inode.c and
drivers/scsi/fcoe/fcoe_transport.c.

>  
>  /* This is called to refresh values for hybla parameters */

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261001112948.322463-1-jiayuan.chen%40linux.dev