From: Peter Zijlstra <peterz@infradead.org>
To: paulmck@kernel.org
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
dipankar@in.ibm.com, akpm@linux-foundation.org,
mathieu.desnoyers@efficios.com, josh@joshtriplett.org,
tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com,
edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com,
joel@joelfernandes.org
Subject: Re: [PATCH tip/core/rcu 1/4] srcu: Fix __call_srcu()/process_srcu() datarace
Date: Mon, 17 Feb 2020 13:42:31 +0100 [thread overview]
Message-ID: <20200217124231.GS14914@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200215002932.15976-1-paulmck@kernel.org>
On Fri, Feb 14, 2020 at 04:29:29PM -0800, paulmck@kernel.org wrote:
> From: "Paul E. McKenney" <paulmck@kernel.org>
>
> The srcu_node structure's ->srcu_gp_seq_needed_exp field is accessed
> locklessly, so updates must use WRITE_ONCE(). This commit therefore
> adds the needed WRITE_ONCE() invocations.
>
> This data race was reported by KCSAN. Not appropriate for backporting
> due to failure being unlikely.
This does indeed look like there can be a failure; but this Changelog
fails to describe an actual problem.
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> kernel/rcu/srcutree.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index 657e6a7..b1edac9 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -550,7 +550,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
> snp->srcu_have_cbs[idx] = gpseq;
> rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1);
> if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq))
> - snp->srcu_gp_seq_needed_exp = gpseq;
> + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq);
> mask = snp->srcu_data_have_cbs[idx];
> snp->srcu_data_have_cbs[idx] = 0;
> spin_unlock_irq_rcu_node(snp);
> @@ -660,7 +660,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
> if (snp == sdp->mynode)
> snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
> if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
> - snp->srcu_gp_seq_needed_exp = s;
> + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);
> spin_unlock_irqrestore_rcu_node(snp, flags);
> }
>
> --
> 2.9.5
>
next prev parent reply other threads:[~2020-02-17 12:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-15 0:29 [PATCH tip/core/rcu 0/4] SRCU updates for v5.7 Paul E. McKenney
2020-02-15 0:29 ` [PATCH tip/core/rcu 1/4] srcu: Fix __call_srcu()/process_srcu() datarace paulmck
2020-02-17 12:42 ` Peter Zijlstra [this message]
2020-02-17 17:01 ` Joel Fernandes
2020-02-17 17:11 ` Peter Zijlstra
2020-02-17 17:46 ` Joel Fernandes
2020-02-17 18:18 ` Paul E. McKenney
2020-02-15 0:29 ` [PATCH tip/core/rcu 2/4] srcu: Fix __call_srcu()/srcu_get_delay() datarace paulmck
2020-02-15 0:29 ` [PATCH tip/core/rcu 3/4] srcu: Fix process_srcu()/srcu_batches_completed() datarace paulmck
2020-02-15 0:29 ` [PATCH tip/core/rcu 4/4] srcu: Add READ_ONCE() to srcu_struct ->srcu_gp_seq load paulmck
2020-02-17 12:45 ` Peter Zijlstra
2020-02-17 18:32 ` Paul E. McKenney
2020-02-17 23:06 ` Paul E. McKenney
2020-02-18 11:46 ` Peter Zijlstra
2020-02-18 21:48 ` Paul E. McKenney
2020-02-18 11:43 ` Peter Zijlstra
2020-02-18 16:34 ` Paul E. McKenney
2020-02-18 20:26 ` Peter Zijlstra
2020-02-18 21:38 ` Paul E. McKenney
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