linux-kernel - Re: [PATCH] skbuff: fix a data race in skb_queue

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Message-Id: <A5748E52-90D8-4B5B-87BD-65F980D79A63@lca.pw>
Date:   Mon, 3 Feb 2020 17:34:34 -0500
From:   Qian Cai <cai@....pw>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, elver@...gle.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] skbuff: fix a data race in skb_queue_len()



> On Feb 3, 2020, at 3:28 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> We added recently skb_queue_empty_lockless() helper, to use in these contexts.
> 
> The fact that we use READ_ONCE() is more of an implementation detail I think.
> 

Make sense. I’ll use lockless in naming instead.

> Also, addressing load-stearing issues without making sure the write side
> is using WRITE_ONCE() might be not enough (even if KCSAN warnings disappear)

I suppose that could be a case. I’ll have,

WRITE_ONCE(list->qlen, list->qlen - 1);

in __skb_unlink() where it had already had a few WRITE_ONCE() for other variables.