From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Jerome Brunet <jbrunet@baylibre.com>
Cc: Kevin Hilman <khilman@baylibre.com>,
Brad Harper <bjharper@gmail.com>,
linux-amlogic@lists.infradead.org, linux-mmc@vger.kernel.org,
linux-rt-users@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mmc: host: meson-gx-mmc: fix possible deadlock condition for preempt_rt
Date: Fri, 25 Sep 2020 15:44:45 +0200 [thread overview]
Message-ID: <20200925134445.rk366jip5ne4x7em@linutronix.de> (raw)
In-Reply-To: <1jzh5e8bld.fsf@starbuckisacylon.baylibre.com>
On 2020-09-25 11:11:42 [+0200], Jerome Brunet wrote:
> I'm not sure about this.
> As you have explained on IRC, I understand that IRQF_ONESHOT is causing
> trouble with RT as the hard IRQ part of the thread will not be migrated
> to a thread. That was certainly not the intent when putting this flag.
That is my understanding as well.
> This seems pretty unsafe to me. Maybe we could improve the driver so it
> copes with this case gracefully. ATM, I don't think it would.
Running the primary handler in hardirq context is bad, because it
invokes meson_mmc_request_done() at the very end. And here:
- mmc_complete_cmd() -> complete_all()
There is a lockdep_assert_RT_in_threaded_ctx() which should trigger.
- led_trigger_event() -> led_trigger_event()
This should trigger a might_sleep() warning somewhere.
So removing IRQF_ONESHOT is okay but it should additionally disable the
IRQ source in meson_mmc_irq() and re-enable back in
meson_mmc_irq_thread(). Otherwise the IRQ remains asserted and may fire
multiple times before the thread has a chance to run.
Sebastian
next prev parent reply other threads:[~2020-09-25 13:44 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 13:04 [PATCH] mmc: host: meson-gx-mmc: fix possible deadlock condition for preempt_rt Brad Harper
2020-09-24 17:01 ` Kevin Hilman
2020-09-25 9:11 ` Jerome Brunet
2020-09-25 13:44 ` Sebastian Andrzej Siewior [this message]
2020-09-25 14:14 ` Jerome Brunet
2020-09-25 15:05 ` Sebastian Andrzej Siewior
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