linux-kernel - Re: [RFC net 1/2] netdev-genl: Hold rcu_read_lock in napi

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Message-ID: <20241112172840.0cf9731f@kernel.org>
Date: Tue, 12 Nov 2024 17:28:40 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Joe Damato <jdamato@...tly.com>
Cc: netdev@...r.kernel.org, pabeni@...hat.com, edumazet@...gle.com,
 amritha.nambiar@...el.com, sridhar.samudrala@...el.com,
 mkarsten@...terloo.ca, stable@...r.kernel.org, "David S. Miller"
 <davem@...emloft.net>, Simon Horman <horms@...nel.org>, Mina Almasry
 <almasrymina@...gle.com>, linux-kernel@...r.kernel.org (open list)
Subject: Re: [RFC net 1/2] netdev-genl: Hold rcu_read_lock in napi_get

On Tue, 12 Nov 2024 18:13:58 +0000 Joe Damato wrote:
> +/* must be called under rcu_read_lock(), because napi_by_id requires it */
> +static struct napi_struct *__do_napi_by_id(unsigned int napi_id,
> +					   struct genl_info *info, int *err)
> +{
> +	struct napi_struct *napi;
> +
> +	napi = napi_by_id(napi_id);
> +	if (napi) {
> +		*err = 0;
> +	} else {
> +		NL_SET_BAD_ATTR(info->extack, info->attrs[NETDEV_A_NAPI_ID]);
> +		*err = -ENOENT;
> +	}
> +
> +	return napi;
> +}

Thanks for the quick follow up! I vote we don't factor this out.
I don't see what it buys us, TBH, normally we factor out code
to avoid having to unlock before return, but this code doesn't
have extra returns...

Just slap an rcu_read_lock / unlock around and that's it?

Feel free to repost soon.