From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: eric.dumazet@gmail.com
Cc: cai@lca.pw, netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] skbuff: fix a data race in skb_queue_len()
Date: Thu, 6 Feb 2020 17:38:44 +0100 [thread overview]
Message-ID: <20200206163844.GA432041@zx2c4.com> (raw)
In-Reply-To: <1580841629-7102-1-git-send-email-cai@lca.pw>
Hi Eric,
On Tue, Feb 04, 2020 at 01:40:29PM -0500, Qian Cai wrote:
> - list->qlen--;
> + WRITE_ONCE(list->qlen, list->qlen - 1);
Sorry I'm a bit late to the party here, but this immediately jumped out.
This generates worse code with a bigger race in some sense:
list->qlen-- is:
0: 83 6f 10 01 subl $0x1,0x10(%rdi)
whereas WRITE_ONCE(list->qlen, list->qlen - 1) is:
0: 8b 47 10 mov 0x10(%rdi),%eax
3: 83 e8 01 sub $0x1,%eax
6: 89 47 10 mov %eax,0x10(%rdi)
Are you sure that's what we want?
Jason
next prev parent reply other threads:[~2020-02-06 16:38 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-04 18:40 [PATCH v3] skbuff: fix a data race in skb_queue_len() Qian Cai
2020-02-06 12:59 ` David Miller
2020-02-06 16:38 ` Jason A. Donenfeld [this message]
2020-02-06 17:10 ` Eric Dumazet
2020-02-06 18:12 ` Jason A. Donenfeld
2020-02-06 18:22 ` Eric Dumazet
2020-02-06 18:43 ` Jason A. Donenfeld
2020-02-06 19:29 ` Marco Elver
2020-02-06 21:55 ` Jason A. Donenfeld
2020-02-07 10:35 ` Marco Elver
2020-02-17 3:24 ` Herbert Xu
2020-02-17 7:39 ` Jason A. Donenfeld
2020-02-17 10:20 ` Herbert Xu
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