netdev - Re: [PATCH net] net: lockless sock_i

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Message-ID: <20250903074131.BclfkWQE@linutronix.de>
Date: Wed, 3 Sep 2025 09:41:31 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
	eric.dumazet@...il.com,
	syzbot+50603c05bbdf4dfdaffa@...kaller.appspotmail.com,
	Kuniyuki Iwashima <kuniyu@...gle.com>
Subject: Re: [PATCH net] net: lockless sock_i_ino()

On 2025-09-02 18:36:03 [+0000], Eric Dumazet wrote:
> Followup of commit c51da3f7a161 ("net: remove sock_i_uid()")
> 
> A recent syzbot report was the trigger for this change.
> 
> Over the years, we had many problems caused by the
> read_lock[_bh](&sk->sk_callback_lock) in sock_i_uid().
> 
> We could fix smc_diag_dump_proto() or make a more radical move:
> 
> Instead of waiting for new syzbot reports, cache the socket
> inode number in sk->sk_ino, so that we no longer
> need to acquire sk->sk_callback_lock in sock_i_ino().
> 
> This makes socket dumps faster (one less cache line miss,
> and two atomic ops avoided).
> 
> Prior art:
> 
> commit 25a9c8a4431c ("netlink: Add __sock_i_ino() for __netlink_diag_dump().")
> commit 4f9bf2a2f5aa ("tcp: Don't acquire inet_listen_hashbucket::lock with disabled BH.")
> commit efc3dbc37412 ("rds: Make rds_sock_lock BH rather than IRQ safe.")
> 
> Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.")
> Reported-by: syzbot+50603c05bbdf4dfdaffa@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/netdev/68b73804.050a0220.3db4df.01d8.GAE@google.com/T/#u
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> Cc: Kuniyuki Iwashima <kuniyu@...gle.com>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

Sebastian