From: "Paul E. McKenney" <paulmck@kernel.org>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org
Subject: Re: [PATCH rcu 10/18] srcutiny: Mark read-side data races
Date: Thu, 29 Jul 2021 06:36:18 -0700 [thread overview]
Message-ID: <20210729133618.GS4397@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <YQJlbEgaAGJvx3iN@boqun-archlinux>
On Thu, Jul 29, 2021 at 04:23:08PM +0800, Boqun Feng wrote:
> On Wed, Jul 21, 2021 at 01:21:18PM -0700, Paul E. McKenney wrote:
> > This commit marks some interrupt-induced read-side data races in
> > __srcu_read_lock(), __srcu_read_unlock(), and srcu_torture_stats_print().
> >
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > ---
> > include/linux/srcutiny.h | 8 ++++----
> > kernel/rcu/srcutiny.c | 2 +-
> > 2 files changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
> > index 0e0cf4d6a72a0..6cfaa0a9a9b96 100644
> > --- a/include/linux/srcutiny.h
> > +++ b/include/linux/srcutiny.h
> > @@ -61,7 +61,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp)
> > int idx;
> >
> > idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
> > - WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1);
> > + WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
> > return idx;
> > }
> >
> > @@ -81,11 +81,11 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
> > {
> > int idx;
> >
> > - idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
> > + idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
>
> This looks very weird, any explanation why we want to put data_race() on
> a READ_ONCE()?
We don't want KCSAN to check this read, but we also don't want the
compiler to mess it up.
Thanx, Paul
> Regards,
> Boqun
>
> > pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
> > tt, tf, idx,
> > - READ_ONCE(ssp->srcu_lock_nesting[!idx]),
> > - READ_ONCE(ssp->srcu_lock_nesting[idx]));
> > + data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
> > + data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
> > }
> >
> > #endif
> > diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> > index 26344dc6483b0..a0ba2ed49bc61 100644
> > --- a/kernel/rcu/srcutiny.c
> > +++ b/kernel/rcu/srcutiny.c
> > @@ -96,7 +96,7 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
> > */
> > void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
> > {
> > - int newval = ssp->srcu_lock_nesting[idx] - 1;
> > + int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
> >
> > WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
> > if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
> > --
> > 2.31.1.189.g2e36527f23
> >
next prev parent reply other threads:[~2021-07-29 13:36 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-21 20:20 [PATCH rcu 0/18] Miscellaneous fixes for v5.15 Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 01/18] rcu: Fix to include first blocked task in stall warning Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 02/18] rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock Paul E. McKenney
2021-08-03 14:24 ` Qais Yousef
2021-08-03 15:52 ` Paul E. McKenney
2021-08-03 16:12 ` Qais Yousef
2021-08-03 16:28 ` Paul E. McKenney
2021-08-03 16:33 ` Qais Yousef
2021-08-04 13:50 ` Qais Yousef
2021-08-04 22:33 ` Paul E. McKenney
2021-08-06 9:56 ` Qais Yousef
2021-08-06 9:57 ` Qais Yousef
2021-08-06 11:43 ` Paul E. McKenney
2021-08-06 12:33 ` Qais Yousef
2021-07-21 20:21 ` [PATCH rcu 03/18] rcu: Remove special bit at the bottom of the ->dynticks counter Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 04/18] rcu: Weaken ->dynticks accesses and updates Paul E. McKenney
2021-07-21 20:41 ` Linus Torvalds
2021-07-21 21:25 ` Paul E. McKenney
2021-07-28 17:37 ` [PATCH v2 " Paul E. McKenney
2021-07-28 17:58 ` Linus Torvalds
2021-07-28 18:12 ` Mathieu Desnoyers
2021-07-28 18:32 ` Linus Torvalds
2021-07-28 18:39 ` Mathieu Desnoyers
2021-07-28 18:46 ` Paul E. McKenney
2021-07-28 18:46 ` Paul E. McKenney
2021-07-28 18:57 ` Linus Torvalds
2021-07-28 18:23 ` Mathieu Desnoyers
2021-07-28 18:58 ` Paul E. McKenney
2021-07-28 19:45 ` Paul E. McKenney
2021-07-28 20:03 ` Mathieu Desnoyers
2021-07-28 20:28 ` Paul E. McKenney
2021-07-29 14:41 ` Mathieu Desnoyers
2021-07-29 15:57 ` Paul E. McKenney
2021-07-29 17:41 ` Mathieu Desnoyers
2021-07-29 18:05 ` Paul E. McKenney
2021-07-29 18:42 ` Mathieu Desnoyers
2021-07-28 20:37 ` Josh Triplett
2021-07-28 20:47 ` Paul E. McKenney
2021-07-28 22:23 ` Frederic Weisbecker
2021-07-29 1:07 ` Paul E. McKenney
2021-07-29 7:58 ` [PATCH " Boqun Feng
2021-07-29 10:53 ` Frederic Weisbecker
2021-07-30 5:56 ` Boqun Feng
2021-07-30 17:18 ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 05/18] rcu: Mark accesses to ->rcu_read_lock_nesting Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 06/18] rculist: Unify documentation about missing list_empty_rcu() Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 07/18] rcu/tree: Handle VM stoppage in stall detection Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 08/18] rcu: Do not disable GP stall detection in rcu_cpu_stall_reset() Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 09/18] rcu: Start timing stall repetitions after warning complete Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 10/18] srcutiny: Mark read-side data races Paul E. McKenney
2021-07-29 8:23 ` Boqun Feng
2021-07-29 13:36 ` Paul E. McKenney [this message]
2021-07-21 20:21 ` [PATCH rcu 11/18] rcu: Mark lockless ->qsmask read in rcu_check_boost_fail() Paul E. McKenney
2021-07-29 8:54 ` Boqun Feng
2021-07-29 14:03 ` Paul E. McKenney
2021-07-30 2:28 ` Boqun Feng
2021-07-30 3:26 ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 12/18] rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stack Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 13/18] rcu: Remove trailing spaces and tabs Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 14/18] rcu: Mark accesses in tree_stall.h Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 15/18] rcu: Remove useless "ret" update in rcu_gp_fqs_loop() Paul E. McKenney
2021-08-03 16:48 ` Joe Perches
2021-08-03 17:10 ` Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 16/18] rcu: Use per_cpu_ptr to get the pointer of per_cpu variable Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 17/18] rcu: Explain why rcu_all_qs() is a stub in preemptible TREE RCU Paul E. McKenney
2021-07-21 20:21 ` [PATCH rcu 18/18] rcu: Print human-readable message for schedule() in RCU reader Paul E. McKenney
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