linux-kernel - [BUG] sleep in atomic in 8250 runtime PM code path

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Message-ID: <20180929132036.0323e24b@xhacker.debian>
Date:   Sat, 29 Sep 2018 13:20:36 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Phil Edworthy <phil.edworthy@...esas.com>
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [BUG] sleep in atomic in 8250 runtime PM code path

Hi,

Recently I found I could trigger sleep in atomic bug on berlin after commit
d76c74387e1c ("serial: 8250_dw: Fix runtime PM handling"). The path looks like:

dw8250_probe => serial850_register_8250_port => uart_add_one_port=>
register_console => console_unlock => univ8250_console_write =>
serial8250_console_write => serial8250_rpm_get => pm_runtime_get_sync

The irq is disabled by printk_safe_enter_irqsave() in console_unlock, but
pm_runtime_get_sync can't be called in atomic context...

I guess the reason why we didn't notice it is due to the fact that
only OMAP and DW sets UART_CAP_RPM currently, and DW set the flag in
May 2018.

Per my understanding, the bug sits in the 8250 core driver rather than
8250_dw.c.

Thanks