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Date:   Tue, 20 Dec 2022 16:36:20 -0500
From:   Adrien Thierry <athierry@redhat.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kevin Hilman <khilman@kernel.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Lorenzo Pieralisi <lpieralisi@kernel.org>,
        Sudeep Holla <sudeep.holla@arm.com>, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Brian Masney <bmasney@redhat.com>,
        linux-rt-users@vger.kernel.org
Subject: Re: [PATCH v2 0/5] PM: Fixes for Realtime systems
Message-ID: <Y6Iq1CyHScvZM++Y@fedora>
References: <20221219151503.385816-1-krzysztof.kozlowski@linaro.org>
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In-Reply-To: <20221219151503.385816-1-krzysztof.kozlowski@linaro.org>
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Hi Krzysztof,
Thanks for looking into this!

I tested your patchset on the QDrive3 on a CentOS Stream 9 RT kernel (I
couldn't test it on mainline because the latest RT patchset only supports
6.1 which is missing some bits needed to boot QDrive3).

It fixes the PSCI cpuidle issue I was encountering in [1]. However, I may
have found another code path that triggers a similar issue:

BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 113, name: kworker/4:2
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
4 locks held by kworker/4:2/113:
 #0: ffff09b0c2376928 ((wq_completion)pm){+.+.}-{0:0}, at: process_one_work+0x1f4/0x7c0
 #1: ffff800008bf3dd0 ((work_completion)(&genpd->power_off_work)){+.+.}-{0:0}, at: process_one_work+0x1f4/0x7c0
 #2: ffff09b0c2e44860 (&genpd->rslock){....}-{2:2}, at: genpd_lock_rawspin+0x20/0x30
 #3: ffff09b0c6696a20 (&dev->power.lock){+.+.}-{2:2}, at: dev_pm_qos_flags+0x2c/0x60
irq event stamp: 170
hardirqs last  enabled at (169): [<ffffa1be822f8a78>] _raw_spin_unlock_irq+0x48/0xc4
hardirqs last disabled at (170): [<ffffa1be822f8df4>] _raw_spin_lock_irqsave+0xb0/0xfc
softirqs last  enabled at (0): [<ffffa1be814cfff0>] copy_process+0x68c/0x1500
softirqs last disabled at (0): [<0000000000000000>] 0x0
Preemption disabled at:
[<ffffa1be81d7e620>] genpd_lock_rawspin+0x20/0x30
CPU: 4 PID: 113 Comm: kworker/4:2 Tainted: G               X --------- ---  5.14.0-rt14+ #2
Hardware name: Qualcomm SA8540 ADP (DT)
Workqueue: pm genpd_power_off_work_fn
Call trace:
 dump_backtrace+0xb4/0x12c
 show_stack+0x1c/0x70
 dump_stack_lvl+0x98/0xd0
 dump_stack+0x14/0x2c
 __might_resched+0x180/0x220
 rt_spin_lock+0x74/0x11c
 dev_pm_qos_flags+0x2c/0x60
 genpd_power_off.part.0.isra.0+0xac/0x2d0
 genpd_power_off_work_fn+0x68/0x8c
 process_one_work+0x2b8/0x7c0
 worker_thread+0x15c/0x44c
 kthread+0xf8/0x104
 ret_from_fork+0x10/0x20

This happens consistently during boot. But on the mainline kernel, this
code path has changed: genpd_power_off no longer calls dev_pm_qos_flags.
So it might not happen on mainline. I hope to be able to test your
patchset again soon on mainline with the next version of the RT patchset
(which should be able to boot the QDrive3).

Best,
Adrien

[1] https://lore.kernel.org/all/20220615203605.1068453-1-athierry@redhat.com/