From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: 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,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 2/5] rcu-tasks: Mark ->trc_reader_nesting data races
Date: Wed, 21 Jul 2021 13:38:15 -0700 [thread overview]
Message-ID: <20210721203818.3398345-2-paulmck@kernel.org> (raw)
In-Reply-To: <20210721203758.GA3386731@paulmck-ThinkPad-P17-Gen-1>
There are several ->trc_reader_nesting data races that are too
low-probability for KCSAN to notice, but which will happen sooner or
later. This commit therefore marks these accesses, and comments one
that cannot race.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tasks.h | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 6a117375a62a1..f6b5320c44849 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -897,7 +897,7 @@ static void trc_read_check_handler(void *t_in)
// If the task is not in a read-side critical section, and
// if this is the last reader, awaken the grace-period kthread.
- if (likely(!t->trc_reader_nesting)) {
+ if (likely(!READ_ONCE(t->trc_reader_nesting))) {
if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
wake_up(&trc_wait);
// Mark as checked after decrement to avoid false
@@ -906,7 +906,7 @@ static void trc_read_check_handler(void *t_in)
goto reset_ipi;
}
// If we are racing with an rcu_read_unlock_trace(), try again later.
- if (unlikely(t->trc_reader_nesting < 0)) {
+ if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0)) {
if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end)))
wake_up(&trc_wait);
goto reset_ipi;
@@ -953,6 +953,7 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
n_heavy_reader_ofl_updates++;
in_qs = true;
} else {
+ // The task is not running, so C-language access is safe.
in_qs = likely(!t->trc_reader_nesting);
}
@@ -985,7 +986,7 @@ static void trc_wait_for_one_reader(struct task_struct *t,
// The current task had better be in a quiescent state.
if (t == current) {
t->trc_reader_checked = true;
- WARN_ON_ONCE(t->trc_reader_nesting);
+ WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
return;
}
@@ -1101,7 +1102,7 @@ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0],
".i"[is_idle_task(t)],
".N"[cpu > 0 && tick_nohz_full_cpu(cpu)],
- t->trc_reader_nesting,
+ READ_ONCE(t->trc_reader_nesting),
" N"[!!t->trc_reader_special.b.need_qs],
cpu);
sched_show_task(t);
@@ -1196,7 +1197,7 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
static void exit_tasks_rcu_finish_trace(struct task_struct *t)
{
WRITE_ONCE(t->trc_reader_checked, true);
- WARN_ON_ONCE(t->trc_reader_nesting);
+ WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
WRITE_ONCE(t->trc_reader_nesting, 0);
if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)))
rcu_read_unlock_trace_special(t, 0);
--
2.31.1.189.g2e36527f23
next prev parent reply other threads:[~2021-07-21 20:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-21 20:37 [PATCH rcu 0/5] Tasks-RCU updates for v5.15 Paul E. McKenney
2021-07-21 20:38 ` [PATCH rcu 1/5] rcu-tasks: Add comments explaining task_struct strategy Paul E. McKenney
2021-07-21 20:38 ` Paul E. McKenney [this message]
2021-07-21 20:38 ` [PATCH rcu 3/5] rcu-tasks: Mark ->trc_reader_special.b.need_qs data races Paul E. McKenney
2021-07-21 20:38 ` [PATCH rcu 4/5] rcu-tasks: Fix synchronize_rcu_rude() typo in comment Paul E. McKenney
2021-07-21 20:38 ` [PATCH rcu 5/5] rcu: Fix macro name CONFIG_TASKS_RCU_TRACE Paul E. McKenney
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210721203818.3398345-2-paulmck@kernel.org \
--to=paulmck@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=dhowells@redhat.com \
--cc=edumazet@google.com \
--cc=fweisbec@gmail.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=kernel-team@fb.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).