linux-kernel - [tip: core/entry] sched: Snapshot thread flags

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Date:   Fri, 26 Nov 2021 20:22:59 -0000
From:   "tip-bot2 for Mark Rutland" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: core/entry] sched: Snapshot thread flags

The following commit has been merged into the core/entry branch of tip:

Commit-ID:     13a405dc6f7f01635c1e849c42b2b8941cec2968
Gitweb:        https://git.kernel.org/tip/13a405dc6f7f01635c1e849c42b2b8941cec2968
Author:        Mark Rutland <mark.rutland@....com>
AuthorDate:    Wed, 17 Nov 2021 16:30:41 
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Fri, 26 Nov 2021 21:20:13 +01:00

sched: Snapshot thread flags

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@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Acked-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lore.kernel.org/r/20211117163050.53986-4-mark.rutland@arm.com
---
 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 3c9b0fd..7ba05de 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8520,7 +8520,7 @@ 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);