Re: Unexplained long boot delays [Was Re: [GIT PULL] RCU changes for v6.9]

From: Florian Fainelli <f.fainelli@gmail.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
	kernel-team@meta.com, paulmck@kernel.org, mingo@kernel.org,
	tglx@linutronix.de, rcu@vger.kernel.org, joel@joelfernandes.org,
	neeraj.upadhyay@amd.com, urezki@gmail.com,
	qiang.zhang1211@gmail.com, frederic@kernel.org,
	bigeasy@linutronix.de, anna-maria@linutronix.de,
	chenzhongjin@huawei.com, yangjihong1@huawei.com,
	rostedt@goodmis.org
Subject: Re: Unexplained long boot delays [Was Re: [GIT PULL] RCU changes for v6.9]
Date: Tue, 12 Mar 2024 14:34:29 -0700	[thread overview]
Message-ID: <c5f9c640-4c06-495e-9c7e-0c208b914fa7@gmail.com> (raw)
In-Reply-To: <ZfDEIs63EBIYBJIC@boqun-archlinux>

On 3/12/24 14:07, Boqun Feng wrote:
> On Tue, Mar 12, 2024 at 01:32:03PM -0700, Florian Fainelli wrote:
>> Hi Boqun,
>>
>> On 3/8/24 09:15, Boqun Feng wrote:
>>> Hi Linus,
>>>
>>> Please pull this for the RCU changes of v6.9:
>>>
>>> The following changes since commit 41bccc98fb7931d63d03f326a746ac4d429c1dd3:
>>>
>>>     Linux 6.8-rc2 (2024-01-28 17:01:12 -0800)
>>>
>>> are available in the Git repository at:
>>>
>>>     git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git tags/rcu.next.v6.9
>>>
>>> for you to fetch changes up to 3add00be5fe5810d7aa5ec3af8b6a245ef33144b:
>>>
>>>     Merge branches 'rcu-doc.2024.02.14a', 'rcu-nocb.2024.02.14a', 'rcu-exp.2024.02.14a', 'rcu-tasks.2024.02.26a' and 'rcu-misc.2024.02.14a' into rcu.2024.02.26a (2024-02-26 17:37:25 -0800)
>>>
>>>
>>> Two merge conflicts were detected by linux-next:
>>>
>>> * https://lore.kernel.org/lkml/20240226135745.12ac854d@canb.auug.org.au/
>>> * https://lore.kernel.org/lkml/20240227125522.2bdbe6be@canb.auug.org.au/
>>>
>>> These conflict resolutions from linux-next look good to me, plus I made
>>> my own resolutions at branch merge/rcu.2024.02.27a for your reference.
>>>
>>>
>>> Some highlights of the changes:
>>>
>>> * Eliminates deadlocks involving do_exit() and RCU tasks, by Paul:
>>>     Instead of SRCU read side critical sections, now a percpu list is used
>>>     in do_exit() for scaning yet-to-exit tasks.
>>>
>>> * Fixes a deadlock due to the dependency between workqueue and RCU
>>>     expedited grace period, reported by Anna-Maria Behnsen and Thomas
>>>     Gleixner and fixed by Frederic: Now RCU expedited always uses its own
>>>     kthread worker instead of a workqueue.
>>
>> At least one device in my test farm (ARM 32-bit) has consistently shown a
>> very long boot, and some others are intermittently affected. This
>> consistently looks like this on most of my devices:
>>
>> [    2.450351] bcmgenet f0480000.ethernet: GENET 5.0 EPHY: 0x0000
>> [    2.547562] ata1: SATA link down (SStatus 0 SControl 300)
>> [  162.107264] unimac-mdio unimac-mdio.0: Broadcom UniMAC MDIO bus
>>
>> this gets flagged by my boot script as a boot failure since we exceeded the
>> 30 seconds timeout given to boot a kernel to a prompt.
>>
>> It has been somewhat difficult to get a reliable bisection going on, but
>> what I am sure of is that e5a3878c947ceef7b6ab68fdc093f3848059842c~1 does
>> not expose the problem for 10 consecutive boots, while I *might* see it at
>> e5a3878c947ceef7b6ab68fdc093f3848059842c and beyond.
>>
>> Any clues what is going on here?
>>
> 
> Could you share the config file and your kernel parameters? Also could
> you share the whole log? Thanks!

Here is the configuration file:

https://gist.github.com/ffainelli/f3fd38752a186cee0cb8719089c0b6b8

and here is a log where this fails:

https://gist.github.com/ffainelli/ed08a2b3e853f59343786ebd20364fc8
-- 
Florian