From: "Xu, Yanfei" <yanfei.xu@windriver.com>
To: paulmck@kernel.org
Cc: josh@joshtriplett.org, rostedt@goodmis.org,
mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com,
joel@joelfernandes.org, rcu@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] rcu: fix a deadlock caused by not release rcu_node->lock
Date: Mon, 17 May 2021 09:55:30 +0800 [thread overview]
Message-ID: <72a3b3f4-1b74-6c03-9d04-ac4bb721a55a@windriver.com> (raw)
In-Reply-To: <20210516225853.GD4441@paulmck-ThinkPad-P17-Gen-1>
On 5/17/21 6:58 AM, Paul E. McKenney wrote:
> [Please note: This e-mail is from an EXTERNAL e-mail address]
>
> On Sun, May 16, 2021 at 05:50:10PM +0800, yanfei.xu@windriver.com wrote:
>> From: Yanfei Xu <yanfei.xu@windriver.com>
>>
>> rcu_node->lock isn't released in rcu_print_task_stall() if the rcu_node
>> don't contain tasks which blocking the GP. However this rcu_node->lock
>> will be used again in rcu_dump_cpu_stacks() soon while the ndetected is
>> non-zero. As a result the cpu will hung by this deadlock.
>>
>> Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled")
>> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
>
> Also a good catch, thank you! Queued for further review and testing,
> wordsmithed as shown below. The rcutorture scripts have been known to
> work on ARM in the past, and might still do so. (I test on x86.)
>
> As always, please check to make sure that I didn't mess something up.
>
Looks good to me, Thanks!
Regards,
Yanfei
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit e0a9b77f245ae4fe1537120fd5319bf9e091618e
> Author: Yanfei Xu <yanfei.xu@windriver.com>
> Date: Sun May 16 17:50:10 2021 +0800
>
> rcu: Fix stall-warning deadlock due to non-release of rcu_node ->lock
>
> If rcu_print_task_stall() is invoked on an rcu_node structure that does
> not contain any tasks blocking the current grace period, it takes an
> early exit that fails to release that rcu_node structure's lock. This
> results in a self-deadlock, which is detected by lockdep.
>
> To reproduce this bug:
>
> tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 3 --trust-make --configs "TREE03" --kconfig "CONFIG_PROVE_LOCKING=y" --bootargs "rcutorture.stall_cpu=30 rcutorture.stall_cpu_block=1 rcutorture.fwd_progress=0 rcutorture.test_boost=0"
>
> This will also result in other complaints, including RCU's scheduler
> hook complaining about blocking rather than preemption and an rcutorture
> writer stall.
>
> Only a partial RCU CPU stall warning message will be printed because of
> the self-deadlock.
>
> This commit therefore releases the lock on the rcu_print_task_stall()
> function's early exit path.
>
> Fixes: c583bcb8f5ed ("rcu: Don't invoke try_invoke_on_locked_down_task() with irqs disabled")
> Signed-off-by: Yanfei Xu <yanfei.xu@windriver.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
>
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index a10ea1f1f81f..d574e3bbd929 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -267,8 +267,10 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags)
> struct task_struct *ts[8];
>
> lockdep_assert_irqs_disabled();
> - if (!rcu_preempt_blocked_readers_cgp(rnp))
> + if (!rcu_preempt_blocked_readers_cgp(rnp)) {
> + raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
> return 0;
> + }
> pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
> rnp->level, rnp->grplo, rnp->grphi);
> t = list_entry(rnp->gp_tasks->prev,
>
prev parent reply other threads:[~2021-05-17 1:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-16 9:50 [PATCH v2] rcu: fix a deadlock caused by not release rcu_node->lock yanfei.xu
2021-05-16 12:33 ` Xu, Yanfei
2021-05-16 22:58 ` Paul E. McKenney
2021-05-17 1:55 ` Xu, Yanfei [this message]
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=72a3b3f4-1b74-6c03-9d04-ac4bb721a55a@windriver.com \
--to=yanfei.xu@windriver.com \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulmck@kernel.org \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.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).