linux-kernel - Re: [PATCH net] net: napi: Make napi_defer

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Message-ID: <CANn89iK+09DW95LTFwN1tA=_hV7xvA0mY4O4d-LwVbmNkO0y3w@mail.gmail.com>
Date: Mon, 2 Sep 2024 15:01:28 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Joe Damato <jdamato@...tly.com>
Cc: netdev@...r.kernel.org, mkarsten@...terloo.ca, stable@...nel.org, 
	Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, Paolo Abeni <pabeni@...hat.com>, 
	Jonathan Corbet <corbet@....net>, Breno Leitao <leitao@...ian.org>, 
	Johannes Berg <johannes.berg@...el.com>, Heiner Kallweit <hkallweit1@...il.com>, 
	Alexander Lobakin <aleksander.lobakin@...el.com>, 
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: napi: Make napi_defer_irqs u32

On Sat, Aug 31, 2024 at 1:32 PM Joe Damato <jdamato@...tly.com> wrote:
>
> In commit 6f8b12d661d0 ("net: napi: add hard irqs deferral feature")
> napi_defer_irqs was added to net_device and napi_defer_irqs_count was
> added to napi_struct, both as type int.
>
> This value never goes below zero. Change the type for both from int to
> u32, and add an overflow check to sysfs to limit the value to S32_MAX.
>
> Before this patch:
>
> $ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
> $ cat /sys/class/net/eth4/napi_defer_hard_irqs
> -2147483647
>
> After this patch:
>
> $ sudo bash -c 'echo 2147483649 > /sys/class/net/eth4/napi_defer_hard_irqs'
> bash: line 0: echo: write error: Numerical result out of range
>
> Fixes: 6f8b12d661d0 ("net: napi: add hard irqs deferral feature")
> Cc: stable@...nel.org
> Cc: Eric Dumazet <edumazet@...gle.com>
> Suggested-by: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Joe Damato <jdamato@...tly.com>
> ---

I do not think this deserves a change to stable trees.

Signed or unsigned, what is the issue ?

Do you really need one extra bit ?

/sys/class/net/XXXXX/tx_queue_len has a similar behavior.