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 2/3] rcu/nocb: Check for migratability rather than pure preemptability
Date: Wed, 21 Jul 2021 12:51:17 +0100 [thread overview]
Message-ID: <20210721115118.729943-3-valentin.schneider@arm.com> (raw)
In-Reply-To: <20210721115118.729943-1-valentin.schneider@arm.com>
Running v5.13-rt1 on my arm64 Juno board triggers:
[ 0.156302] =============================
[ 0.160416] WARNING: suspicious RCU usage
[ 0.164529] 5.13.0-rt1 #20 Not tainted
[ 0.168300] -----------------------------
[ 0.172409] kernel/rcu/tree_plugin.h:69 Unsafe read of RCU_NOCB offloaded state!
[ 0.179920]
[ 0.179920] other info that might help us debug this:
[ 0.179920]
[ 0.188037]
[ 0.188037] rcu_scheduler_active = 1, debug_locks = 1
[ 0.194677] 3 locks held by rcuc/0/11:
[ 0.198448] #0: ffff00097ef10cf8 ((softirq_ctrl.lock).lock){+.+.}-{2:2}, at: __local_bh_disable_ip (./include/linux/rcupdate.h:662 kernel/softirq.c:171)
[ 0.208709] #1: ffff80001205e5f0 (rcu_read_lock){....}-{1:2}, at: rt_spin_lock (kernel/locking/spinlock_rt.c:43 (discriminator 4))
[ 0.217134] #2: ffff80001205e5f0 (rcu_read_lock){....}-{1:2}, at: __local_bh_disable_ip (kernel/softirq.c:169)
[ 0.226428]
[ 0.226428] stack backtrace:
[ 0.230889] CPU: 0 PID: 11 Comm: rcuc/0 Not tainted 5.13.0-rt1 #20
[ 0.237100] Hardware name: ARM Juno development board (r0) (DT)
[ 0.243041] Call trace:
[ 0.245497] dump_backtrace (arch/arm64/kernel/stacktrace.c:163)
[ 0.249185] show_stack (arch/arm64/kernel/stacktrace.c:219)
[ 0.252522] dump_stack (lib/dump_stack.c:122)
[ 0.255947] lockdep_rcu_suspicious (kernel/locking/lockdep.c:6439)
[ 0.260328] rcu_rdp_is_offloaded (kernel/rcu/tree_plugin.h:69 kernel/rcu/tree_plugin.h:58)
[ 0.264537] rcu_core (kernel/rcu/tree.c:2332 kernel/rcu/tree.c:2398 kernel/rcu/tree.c:2777)
[ 0.267786] rcu_cpu_kthread (./include/linux/bottom_half.h:32 kernel/rcu/tree.c:2876)
[ 0.271644] smpboot_thread_fn (kernel/smpboot.c:165 (discriminator 3))
[ 0.275767] kthread (kernel/kthread.c:321)
[ 0.279013] ret_from_fork (arch/arm64/kernel/entry.S:1005)
In this case, this is the RCU core kthread accessing the local CPU's
rdp. Before that, rcu_cpu_kthread() invokes local_bh_disable().
Under !CONFIG_PREEMPT_RT (and rcutree.use_softirq=0), this ends up
incrementing the preempt_count, which satisfies the "local non-preemptible
read" of rcu_rdp_is_offloaded().
Under CONFIG_PREEMPT_RT however, this becomes
local_lock(&softirq_ctrl.lock)
which, under the same config, is migrate_disable() + rt_spin_lock().
This *does* prevent the task from migrating away, but not in a way
rcu_rdp_is_offloaded() can notice. Note that the invoking task is an
smpboot thread, and thus cannot be migrated away in the first place.
Check is_pcpu_safe() here rather than preemptible().
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
---
kernel/rcu/tree_plugin.h | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index ad0156b86937..6c3c4100da83 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -70,8 +70,7 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
!(lockdep_is_held(&rcu_state.barrier_mutex) ||
(IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
rcu_lockdep_is_held_nocb(rdp) ||
- (rdp == this_cpu_ptr(&rcu_data) &&
- !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
+ (rdp == this_cpu_ptr(&rcu_data) && is_pcpu_safe()) ||
rcu_current_is_nocb_kthread(rdp) ||
rcu_running_nocb_timer(rdp)),
"Unsafe read of RCU_NOCB offloaded state"
--
2.25.1
next prev parent reply other threads:[~2021-07-21 11:58 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 ` [PATCH 1/3] sched: Introduce is_pcpu_safe() Valentin Schneider
2021-07-27 16:23 ` Paul E. McKenney
2021-07-21 11:51 ` Valentin Schneider [this message]
2021-07-27 16:24 ` [PATCH 2/3] rcu/nocb: Check for migratability rather than pure preemptability 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
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=20210721115118.729943-3-valentin.schneider@arm.com \
--to=valentin.schneider@arm.com \
--cc=anshuman.khandual@arm.com \
--cc=ardb@kernel.org \
--cc=bristot@redhat.com \
--cc=catalin.marinas@arm.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=rostedt@goodmis.org \
--cc=steven.price@arm.com \
--cc=tglx@linutronix.de \
--cc=vincenzo.frascino@arm.com \
--cc=will@kernel.org \
/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).