[PATCH v5 03/10] sched: snapshot thread flags

From: Mark Rutland <mark.rutland@arm.com>
To: linux-kernel@vger.kernel.org
Cc: benh@kernel.crashing.org, boqun.feng@gmail.com, bp@alien8.de,
	catalin.marinas@arm.com, dvyukov@google.com, elver@google.com,
	ink@jurassic.park.msu.ru, jonas@southpole.se,
	juri.lelli@redhat.com, linux@armlinux.org.uk, luto@kernel.org,
	mark.rutland@arm.com, mattst88@gmail.com,
	michal.simek@xilinx.com, mingo@redhat.com, mpe@ellerman.id.au,
	paulmck@kernel.org, paulus@samba.org, peterz@infradead.org,
	rth@twiddle.net, shorne@gmail.com,
	stefan.kristiansson@saunalahti.fi, tglx@linutronix.de,
	vincent.guittot@linaro.org, will@kernel.org
Subject: [PATCH v5 03/10] sched: snapshot thread flags
Date: Tue, 14 Sep 2021 11:30:20 +0100	[thread overview]
Message-ID: <20210914103027.53565-4-mark.rutland@arm.com> (raw)
In-Reply-To: <20210914103027.53565-1-mark.rutland@arm.com>

Some thread flags can be set remotely, and so even when IRQs are
disabled, the flags can change under our feet. Generally this is
unlikely to cause a problem in practice, but it is somewhat unsound, and
KCSAN will legitimately warn that there is a data race.

To avoid such issues, a snapshot of the flags has to be taken prior to
using them. Some places already use READ_ONCE() for that, others do not.

Convert them all to the new flag accessor helpers.

The READ_ONCE(ti->flags) .. cmpxchg(ti->flags) loop in
set_nr_if_polling() is left as-is for clarity.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1bba4128a3e6..b65876b5d64c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8538,7 +8538,7 @@ void sched_show_task(struct task_struct *p)
 	rcu_read_unlock();
 	pr_cont(" stack:%5lu pid:%5d ppid:%6d flags:0x%08lx\n",
 		free, task_pid_nr(p), ppid,
-		(unsigned long)task_thread_info(p)->flags);
+		read_task_thread_flags(p));
 
 	print_worker_info(KERN_INFO, p);
 	print_stop_info(KERN_INFO, p);
-- 
2.11.0

