From: Peter Zijlstra <peterz@infradead.org>
To: Anatol Pomozov <anatol.pomozov@gmail.com>
Cc: fw@strlen.de, Dmitry Vyukov <dvyukov@google.com>,
paulmck@linux.ibm.com, LKML <linux-kernel@vger.kernel.org>
Subject: Re: seqcount usage in xt_replace_table()
Date: Thu, 10 Jan 2019 13:44:27 +0100 [thread overview]
Message-ID: <20190110124427.GB21224@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAOMFOmU=t9YbE68YpoQn0Ug0XN1F+0iuJp9J=htCRRrbdaPSVA@mail.gmail.com>
On Tue, Jan 08, 2019 at 11:33:39AM -0800, Anatol Pomozov wrote:
> Hello folks,
>
> A bit of context what I am doing. I am trying to port KTSAN (Kernel
> Thread Sanitizer) tool to v4.20. That tool tracks shared data usage
> and makes sure it is accessed in a thread-safe manner.
>
> seqlock is a synchronization primitive used by Linux kernel. KTSAN
> annotates read_seqbegin()/read_seqretry() and tracks what data been
> accessed in its critical section.
>
> During KTSAN port I found and interesting seqcount usage introduced in
> commit 80055dab5de0c8677bc148c4717ddfc753a9148e
>
> If I read this commit correctly xt_replace_table() does not use
> seqlock in a canonical way to specify a critical section. Instead the
> code reads the counter and waits until it gets to a specific value.
(gets away from)
> Now I want KTSAN to play with this code nicely. I need to tell KTSAN
> something like "this raw_read_seqcount() does not start a critical
> section, just ignore it". So temporary I introduced
> raw_read_seqcount_nocritical() function that is ignored by KTSAN. Is
> it a good solution?
This code is special enough to just do: READ_ONCE(->sequence) and be
done with it. It doesn't need the smp_rmb() or anything else.
next prev parent reply other threads:[~2019-01-10 12:44 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-08 19:33 seqcount usage in xt_replace_table() Anatol Pomozov
2019-01-08 22:37 ` Florian Westphal
2019-01-10 12:41 ` Peter Zijlstra
2019-01-10 12:53 ` Dmitry Vyukov
2019-01-10 20:18 ` Peter Zijlstra
2019-01-10 14:48 ` Florian Westphal
2019-01-10 20:20 ` Peter Zijlstra
2019-01-10 20:25 ` Peter Zijlstra
2019-01-10 22:29 ` Florian Westphal
2019-01-11 8:34 ` Peter Zijlstra
2019-01-11 14:08 ` Paul E. McKenney
2019-01-10 14:52 ` Paul E. McKenney
2019-01-09 0:02 ` Andrea Parri
2019-01-09 0:36 ` Anatol Pomozov
2019-01-09 5:35 ` Dmitry Vyukov
2019-01-09 11:24 ` Andrea Parri
2019-01-09 11:55 ` Dmitry Vyukov
2019-01-09 12:11 ` Andrea Parri
2019-01-09 12:29 ` Dmitry Vyukov
2019-01-09 17:10 ` Paul E. McKenney
2019-01-10 8:49 ` Dmitry Vyukov
2019-01-10 12:30 ` Andrea Parri
2019-01-10 12:38 ` Dmitry Vyukov
2019-01-10 12:46 ` Andrea Parri
2019-01-10 13:25 ` Dmitry Vyukov
2019-01-10 14:50 ` Paul E. McKenney
2019-01-10 12:44 ` Peter Zijlstra [this message]
2019-01-10 12:54 ` Dmitry Vyukov
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