From: Valentin Schneider <valentin.schneider@arm.com>
To: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-rt-users@vger.kernel.org
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Steven Price <steven.price@arm.com>,
Ard Biesheuvel <ardb@kernel.org>
Subject: [PATCH 1/3] sched: Introduce is_pcpu_safe()
Date: Wed, 21 Jul 2021 12:51:16 +0100 [thread overview]
Message-ID: <20210721115118.729943-2-valentin.schneider@arm.com> (raw)
In-Reply-To: <20210721115118.729943-1-valentin.schneider@arm.com>
Some areas use preempt_disable() + preempt_enable() to safely access
per-CPU data. The PREEMPT_RT folks have shown this can also be done by
keeping preemption enabled and instead disabling migration (and acquiring a
sleepable lock, if relevant).
Introduce a helper which checks whether the current task can safely access
per-CPU data, IOW if the task's context guarantees the accesses will target
a single CPU. This accounts for preemption, CPU affinity, and migrate
disable - note that the CPU affinity check also mandates the presence of
PF_NO_SETAFFINITY, as otherwise userspace could concurrently render the
upcoming per-CPU access(es) unsafe.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
include/linux/sched.h | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index efdbdf654876..7ce2d5c1ad55 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1707,6 +1707,16 @@ static inline bool is_percpu_thread(void)
#endif
}
+/* Is the current task guaranteed not to be migrated elsewhere? */
+static inline bool is_pcpu_safe(void)
+{
+#ifdef CONFIG_SMP
+ return !preemptible() || is_percpu_thread() || current->migration_disabled;
+#else
+ return true;
+#endif
+}
+
/* Per-process atomic flags. */
#define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */
#define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */
--
2.25.1
next prev parent reply other threads:[~2021-07-21 12:01 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-21 11:51 [PATCH 0/3] sched: migrate_disable() vs per-CPU access safety checks Valentin Schneider
2021-07-21 11:51 ` Valentin Schneider [this message]
2021-07-27 16:23 ` [PATCH 1/3] sched: Introduce is_pcpu_safe() Paul E. McKenney
2021-07-21 11:51 ` [PATCH 2/3] rcu/nocb: Check for migratability rather than pure preemptability Valentin Schneider
2021-07-27 16:24 ` Paul E. McKenney
2021-07-27 23:08 ` Frederic Weisbecker
2021-07-28 19:34 ` Valentin Schneider
2021-07-28 22:01 ` Frederic Weisbecker
2021-07-29 1:04 ` Paul E. McKenney
2021-07-29 10:51 ` Valentin Schneider
2021-07-21 11:51 ` [PATCH 3/3] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider
2021-07-27 19:45 ` [PATCH 0/3] sched: migrate_disable() vs per-CPU access safety checks Thomas Gleixner
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