From: Florian Westphal <fw@strlen.de>
To: Will Deacon <will@kernel.org>
Cc: Florian Westphal <fw@strlen.de>,
subashab@codeaurora.org, pablo@netfilter.org,
Sean Tranchetti <stranche@codeaurora.org>,
netfilter-devel@vger.kernel.org, peterz@infradead.org,
tglx@linutronix.de
Subject: Re: [PATCH nf] x_tables: Properly close read section with read_seqcount_retry
Date: Wed, 18 Nov 2020 14:14:19 +0100 [thread overview]
Message-ID: <20201118131419.GK22792@breakpoint.cc> (raw)
In-Reply-To: <20201118125406.GA2029@willie-the-truck>
Will Deacon <will@kernel.org> wrote:
> > diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> > index af22dbe85e2c..b5911985d1eb 100644
> > --- a/net/netfilter/x_tables.c
> > +++ b/net/netfilter/x_tables.c
> > @@ -1384,7 +1384,7 @@ xt_replace_table(struct xt_table *table,
> > * private.
> > */
> > smp_wmb();
> > - table->private = newinfo;
> > + WRITE_ONCE(table->private, newinfo);
>
> ... you could make this rcu_assign_pointer() and get rid of the preceding
> smp_wmb()...
Yes, it would make sense to add proper rcu annotation as well.
> > /* make sure all cpus see new ->private value */
> > smp_wmb();
>
> ... and this smp_wmb() is no longer needed because synchronize_rcu()
> takes care of the ordering.
Right, thanks.
> > @@ -1394,19 +1394,7 @@ xt_replace_table(struct xt_table *table,
> > * may still be using the old entries...
> > */
> > local_bh_enable();
> > -
> > - /* ... so wait for even xt_recseq on all cpus */
> > - for_each_possible_cpu(cpu) {
> > - seqcount_t *s = &per_cpu(xt_recseq, cpu);
> > - u32 seq = raw_read_seqcount(s);
> > -
> > - if (seq & 1) {
> > - do {
> > - cond_resched();
> > - cpu_relax();
> > - } while (seq == raw_read_seqcount(s));
> > - }
> > - }
>
> Do we still need xt_write_recseq_{begin,end}() with this removed?
Yes, it enables userspace to get stable per rule packet and byte counters.
next prev parent reply other threads:[~2020-11-18 13:14 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-14 2:21 [PATCH nf] x_tables: Properly close read section with read_seqcount_retry Sean Tranchetti
2020-11-14 16:53 ` Florian Westphal
2020-11-16 6:32 ` subashab
2020-11-16 14:18 ` Florian Westphal
2020-11-16 16:26 ` subashab
2020-11-16 17:04 ` Florian Westphal
2020-11-16 17:51 ` subashab
2020-11-16 18:20 ` Florian Westphal
2020-11-18 12:13 ` Will Deacon
2020-11-18 12:42 ` Florian Westphal
2020-11-18 12:54 ` Will Deacon
2020-11-18 13:14 ` Florian Westphal [this message]
2020-11-18 20:39 ` subashab
2020-11-18 21:10 ` Florian Westphal
2020-11-20 5:53 ` subashab
2020-11-20 6:31 ` Florian Westphal
2020-11-20 9:44 ` Peter Zijlstra
2020-11-20 9:53 ` Peter Zijlstra
2020-11-20 10:20 ` Florian Westphal
2020-11-20 10:47 ` Peter Zijlstra
2020-11-21 1:27 ` subashab
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