linux-kernel - Re: [PATCH v2] serial: mctrl_gpio: add parameter to skip sync

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Message-ID: <1274bae7-e473-4711-9235-de0aeeadb02f@bootlin.com>
Date: Fri, 14 Feb 2025 09:44:01 +0100
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jiri Slaby <jirislaby@...nel.org>,
 Richard Genoud <richard.genoud@...tlin.com>,
 Nicolas Ferre <nicolas.ferre@...rochip.com>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 Claudiu Beznea <claudiu.beznea@...on.dev>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>,
 Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jonathan Corbet <corbet@....net>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev,
 linux-stm32@...md-mailman.stormreply.com, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2] serial: mctrl_gpio: add parameter to skip sync

On 2/14/25 09:38, Alexis Lothoré wrote:
> The following splat has been observed on a SAMA5D27 platform using
> atmel_serial:
> 
> BUG: sleeping function called from invalid context at kernel/irq/manage.c:738
> in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 27, name: kworker/u5:0
> preempt_count: 1, expected: 0
> INFO: lockdep is turned off.
> irq event stamp: 0
> hardirqs last  enabled at (0): [<00000000>] 0x0
> hardirqs last disabled at (0): [<c01588f0>] copy_process+0x1c4c/0x7bec
> softirqs last  enabled at (0): [<c0158944>] copy_process+0x1ca0/0x7bec
> softirqs last disabled at (0): [<00000000>] 0x0
> CPU: 0 UID: 0 PID: 27 Comm: kworker/u5:0 Not tainted 6.13.0-rc7+ #74
> Hardware name: Atmel SAMA5
> Workqueue: hci0 hci_power_on [bluetooth]
> Call trace:
>   unwind_backtrace from show_stack+0x18/0x1c
>   show_stack from dump_stack_lvl+0x44/0x70
>   dump_stack_lvl from __might_resched+0x38c/0x598
>   __might_resched from disable_irq+0x1c/0x48
>   disable_irq from mctrl_gpio_disable_ms+0x74/0xc0
>   mctrl_gpio_disable_ms from atmel_disable_ms.part.0+0x80/0x1f4
>   atmel_disable_ms.part.0 from atmel_set_termios+0x764/0x11e8
>   atmel_set_termios from uart_change_line_settings+0x15c/0x994
>   uart_change_line_settings from uart_set_termios+0x2b0/0x668
>   uart_set_termios from tty_set_termios+0x600/0x8ec
>   tty_set_termios from ttyport_set_flow_control+0x188/0x1e0
>   ttyport_set_flow_control from wilc_setup+0xd0/0x524 [hci_wilc]
>   wilc_setup [hci_wilc] from hci_dev_open_sync+0x330/0x203c [bluetooth]
>   hci_dev_open_sync [bluetooth] from hci_dev_do_open+0x40/0xb0 [bluetooth]
>   hci_dev_do_open [bluetooth] from hci_power_on+0x12c/0x664 [bluetooth]
>   hci_power_on [bluetooth] from process_one_work+0x998/0x1a38
>   process_one_work from worker_thread+0x6e0/0xfb4
>   worker_thread from kthread+0x3d4/0x484
>   kthread from ret_from_fork+0x14/0x28
> 
> This warning is emitted when trying to toggle, at the highest level,
> some flow control (with serdev_device_set_flow_control) in a device
> driver. At the lowest level, the atmel_serial driver is using
> serial_mctrl_gpio lib to enable/disable the corresponding IRQs
> accordingly.  The warning emitted by CONFIG_DEBUG_ATOMIC_SLEEP is due to
> disable_irq (called in mctrl_gpio_disable_ms) being possibly called in
> some atomic context (some tty drivers perform modem lines configuration
> in regions protected by port lock).
> 
> Split mctrl_gpio_disable_ms into two differents APIs, a non-blocking one
> and a blocking one. Replace mctrl_gpio_disable_ms calls with the
> relevant version depending on whether the call is protected by some port
> lock.
> 
> Suggested-by: Jiri Slaby <jirislaby@...nel.org>
> Signed-off-by: Alexis Lothoré <alexis.lothore@...tlin.com>

So despite changing the commit description, I forgot to update the actual commit
message, which is eventually not adding a flag anymore but new APIs. v3 will
follow, sorry for the noise.

Alexis


-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com