From: Hans de Goede <hdegoede@redhat.com>
To: Serge Semin <Sergey.Semin@baikalelectronics.ru>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Serge Semin <fancer.lancer@gmail.com>,
Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
Andy Shevchenko <andy.shevchenko@gmail.com>,
Maxime Ripard <mripard@kernel.org>, Will Deacon <will@kernel.org>,
Russell King <linux@armlinux.org.uk>,
linux-arm-kernel@lists.infradead.org,
linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] serial: 8250_dw: Fix clk-notifier/port suspend deadlock
Date: Sun, 27 Sep 2020 17:01:52 +0200 [thread overview]
Message-ID: <e508b9c8-bcc4-00a6-0ca0-0b4a0c34f626@redhat.com> (raw)
In-Reply-To: <20200923161950.6237-1-Sergey.Semin@baikalelectronics.ru>
Hi,
On 9/23/20 6:19 PM, Serge Semin wrote:
> Hans has discovered that there is a potential deadlock between the ref
> clock change notifier and the port suspension procedures {see the link at
> the bottom of the letter}. Indeed the deadlock is possible if the port
> suspension is initiated during the ref clock rate change:
>
> CPU0 (suspend CPU/UART) CPU1 (update clock)
> ---- ----
> lock(&port->mutex);
> lock((work_completion)(&data->clk_work));
> lock(&port->mutex);
> lock((work_completion)(&data->clk_work));
>
> *** DEADLOCK ***
>
> So the CPU performing the UART port shutdown procedure will wait until the
> ref clock change notifier is finished (worker is flushed), while the later
> will wait for a port mutex being released.
>
> A possible solution to bypass the deadlock is to move the worker flush out
> of the critical section protected by the TTY port mutex. For instance we
> can register and de-register the clock change notifier in the port probe
> and remove methods instead of having them called from the port
> startup/shutdown callbacks. But in order to do that we need to make sure
> that the serial8250_update_uartclk() method is safe to be used while the
> port is shutted down. Alas the current implementation doesn't provide that
> safety. The solution described above is introduced in the framework of
> this patchset. See individual patches for details.
>
> Link: https://lore.kernel.org/linux-serial/f1cd5c75-9cda-6896-a4e2-42c5bfc3f5c3@redhat.com
>
> Hans, could you test the patchset out on your Cherry Trail (x86)-based
> devices? After that we can merge it in into the kernels 5.8 and 5.9 if
> there is no objections against the fix.
Done, I can confirm that this fixes the lockdep issue for me, so you
can add my:
Tested-by: Hans de Goede <hdegoede@redhat.com>
To the entire series.
Regards,
Hans
next prev parent reply other threads:[~2020-09-27 15:02 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 16:19 [PATCH 0/3] serial: 8250_dw: Fix clk-notifier/port suspend deadlock Serge Semin
2020-09-23 16:19 ` [PATCH 1/3] serial: 8250: Discard RTS/DTS setting from clock update method Serge Semin
2020-09-23 16:19 ` [PATCH 2/3] serial: 8250: Skip uninitialized TTY port baud rate update Serge Semin
2020-09-23 16:19 ` [PATCH 3/3] serial: 8250_dw: Fix clk-notifier/port suspend deadlock Serge Semin
2020-10-18 0:32 ` Jonathan Liu
2020-09-27 15:01 ` Hans de Goede [this message]
2020-09-29 20:51 ` [PATCH 0/3] " Serge Semin
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