netdev - Re: [PATCH net-next] ipv4: Use READ/WRITE_ONCE() for IP local_port

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Date: Wed, 29 Nov 2023 22:06:21 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: David Laight <David.Laight@...lab.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Stephen Hemminger <stephen@...workplumber.org>, 
	David Ahern <dsahern@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"jakub@...udflare.com" <jakub@...udflare.com>
Subject: Re: [PATCH net-next] ipv4: Use READ/WRITE_ONCE() for IP local_port_range

On Wed, Nov 29, 2023 at 8:26 PM David Laight <David.Laight@...lab.com> wrote:
>
> Commit 227b60f5102cd added a seqlock to ensure that the low and high
> port numbers were always updated together.
> This is overkill because the two 16bit port numbers can be held in
> a u32 and read/written in a single instruction.
>
> More recently 91d0b78c5177f added support for finer per-socket limits.
> The user-supplied value is 'high << 16 | low' but they are held
> separately and the socket options protected by the socket lock.
>
> Use a u32 containing 'high << 16 | low' for both the 'net' and 'sk'
> fields and use READ_ONCE()/WRITE_ONCE() to ensure both values are
> always updated together.
>
> Change (the now trival) inet_get_local_port_range() to a static inline
> to optimise the calling code.
> (In particular avoiding returning integers by reference.)
>
> Signed-off-by: David Laight <david.laight@...lab.com>

Nice, I had this patch on my TODO list :)