Date: Tue, 9 Feb 2021 20:42:38 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Lutz Donnerhacke <donner@freebsd.org> Cc: src-committers@freebsd.org, dev-commits-src-all@freebsd.org, dev-commits-src-main@freebsd.org Subject: Re: git: 011b7317dbb5 - main - netgraph/ng_bridge: Document staleness in multithreaded operation Message-ID: <CAGudoHFb6=LSs%2BU9_sY%2Bd1bZwEEdcyjuQQzihsctggqYOqYmnQ@mail.gmail.com> In-Reply-To: <202102091925.119JPSho062759@gitrepo.freebsd.org> References: <202102091925.119JPSho062759@gitrepo.freebsd.org>
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Things like this are best sorted out with atomic_store, otherwise you
may fall victim of various compiler mischief (even if it happens to be
harmless for the time being).
iow all ->staleness accesses should be converted to atomic_*.
grep finds this in ng_bridge_timeout:
if (++host->staleness >= priv->conf.maxStaleness) {
the code should probably explain how this is synchronized against said zeroing
On 2/9/21, Lutz Donnerhacke <donner@freebsd.org> wrote:
> The branch main has been updated by donner:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=011b7317dbb5038a95b9b4fca050325a62f3991e
>
> commit 011b7317dbb5038a95b9b4fca050325a62f3991e
> Author: Lutz Donnerhacke <donner@FreeBSD.org>
> AuthorDate: 2021-02-09 11:32:46 +0000
> Commit: Lutz Donnerhacke <donner@FreeBSD.org>
> CommitDate: 2021-02-09 19:09:05 +0000
>
> netgraph/ng_bridge: Document staleness in multithreaded operation
>
> In the data path of ng_bridge(4), the only value of the host struct,
> which needs to be modified, is the staleness, which is reset every
> time a frame is received. It's save to leave the code as it is.
>
> This patch is part of a series to make ng_bridge(4) multithreaded.
>
> Reviewed by: kp
> MFC after: 2 weeks
> Differential Revision: https://reviews.freebsd.org/D28546
> ---
> sys/netgraph/ng_bridge.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/sys/netgraph/ng_bridge.c b/sys/netgraph/ng_bridge.c
> index 6e3f993d591b..29ab2c715aa7 100644
> --- a/sys/netgraph/ng_bridge.c
> +++ b/sys/netgraph/ng_bridge.c
> @@ -739,7 +739,10 @@ ng_bridge_rcvdata(hook_p hook, item_p item)
>
> /* Look up packet's source Ethernet address in hashtable */
> if ((host = ng_bridge_get(priv, eh->ether_shost)) != NULL) {
> - /* Update time since last heard from this host */
> + /* Update time since last heard from this host.
> + * This is safe without locking, because it's
> + * the only operation during shared access.
> + */
> host->staleness = 0;
>
> /* Did host jump to a different link? */
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--
Mateusz Guzik <mjguzik gmail.com>
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