lockdep detects the following circular locking dependency:
CPU 0 CPU 1
========================== ============================
cdns_uart_isr() printk()
uart_port_lock(port) console_lock()
cdns_uart_console_write()
if (!port->sysrq)
uart_port_lock(port)
uart_handle_break()
port->sysrq = ...
uart_handle_sysrq_char()
printk()
console_lock()
The fixed commit attempts to avoid this situation by only taking the
port lock in cdns_uart_console_write if port->sysrq unset. However, if
(as shown above) cdns_uart_console_write runs before port->sysrq is set,
then it will try to take the port lock anyway. This may result in a
deadlock.
Fix this by splitting sysrq handling into two parts. We use the prepare
helper under the port lock and defer handling until we release the lock.
Fixes: 74ea66d4ca ("tty: xuartps: Improve sysrq handling")
Signed-off-by: Sean Anderson <sean.anderson@linux.dev>
Cc: stable@vger.kernel.org # c980248179: serial: xilinx_uartps: Use port lock wrappers
Acked-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20250110213822.2107462-1-sean.anderson@linux.dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
After commit 0edb555a65 ("platform: Make platform_driver::remove()
return void") .remove() is (again) the right callback to implement for
platform drivers.
Convert all platform drivers below drivers/tty/serial to use .remove(),
with the eventual goal to drop struct platform_driver::remove_new(). As
.remove() and .remove_new() have the same prototypes, conversion is done
by just changing the structure member name in the driver initializer.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20241007205803.444994-7-u.kleine-koenig@baylibre.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The .remove() callback for a platform driver returns an int which makes
many driver authors wrongly assume it's possible to do error handling by
returning an error code. However the value returned is ignored (apart
from emitting a warning) and this typically results in resource leaks.
To improve here there is a quest to make the remove callback return
void. In the first step of this quest all drivers are converted to
.remove_new(), which already returns void. Eventually after all drivers
are converted, .remove_new() will be renamed to .remove().
Trivially convert this driver from always returning zero in the remove
callback to the void returning variant.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20231110152927.70601-53-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
When a serial port is used for kernel console output, then all
modifications to the UART registers which are done from other contexts,
e.g. getty, termios, are interference points for the kernel console.
So far this has been ignored and the printk output is based on the
principle of hope. The rework of the console infrastructure which aims to
support threaded and atomic consoles, requires to mark sections which
modify the UART registers as unsafe. This allows the atomic write function
to make informed decisions and eventually to restore operational state. It
also allows to prevent the regular UART code from modifying UART registers
while printk output is in progress.
All modifications of UART registers are guarded by the UART port lock,
which provides an obvious synchronization point with the console
infrastructure.
To avoid adding this functionality to all UART drivers, wrap the
spin_[un]lock*() invocations for uart_port::lock into helper functions
which just contain the spin_[un]lock*() invocations for now. In a
subsequent step these helpers will gain the console synchronization
mechanisms.
Converted with coccinelle. No functional change.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20230914183831.587273-75-john.ogness@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The return value is only ever used as a return value for remove callbacks
of platform drivers. This return value is ignored by the driver core.
(The only effect is an error message, but uart_remove_one_port() already
emitted one in this case.)
So the return value isn't used at all and uart_remove_one_port() can be
changed to return void without any loss. Also this better matches the
Linux device model as remove functions are not supposed to fail.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230512173810.131447-3-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Pull tty/serial driver updates from Greg KH:
"Here is the "big" set of tty/serial driver changes for 6.2-rc1.
As in previous kernel releases, nothing big here at all, just some
small incremental serial/tty layer cleanups and some individual driver
additions and fixes. Highlights are:
- serial helper macros from Jiri Slaby to reduce the amount of
duplicated code in serial drivers
- api cleanups and consolidations from Ilpo Järvinen in lots of
serial drivers
- the usual set of n_gsm fixes from Daniel Starke as that code gets
exercised more
- TIOCSTI is finally able to be disabled if requested (security
hardening feature from Kees Cook)
- fsl_lpuart driver fixes and features added
- other small serial driver additions and fixes
All of these have been in linux-next for a while with no reported
problems"
* tag 'tty-6.2-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (97 commits)
serial: atmel: don't stop the transmitter when doing PIO
serial: atmel: cleanup atmel_start+stop_tx()
tty: serial: fsl_lpuart: switch to new dmaengine_terminate_* API
serial: sunsab: Fix error handling in sunsab_init()
serial: altera_uart: fix locking in polling mode
serial: pch: Fix PCI device refcount leak in pch_request_dma()
tty: serial: fsl_lpuart: Use pm_ptr() to avoid need to make pm __maybe_unused
tty: serial: fsl_lpuart: Add runtime pm support
tty: serial: fsl_lpuart: enable wakeup source for lpuart
serdev: Replace poll loop by readx_poll_timeout() macro
tty: synclink_gt: unwind actions in error path of net device open
serial: stm32: move dma_request_chan() before clk_prepare_enable()
dt-bindings: serial: xlnx,opb-uartlite: Drop 'contains' from 'xlnx,use-parity'
serial: pl011: Do not clear RX FIFO & RX interrupt in unthrottle.
serial: amba-pl011: avoid SBSA UART accessing DMACR register
tty: serial: altera_jtaguart: remove struct altera_jtaguart
tty: serial: altera_jtaguart: use uart_port::read_status_mask
tty: serial: altera_jtaguart: remove unused altera_jtaguart::sigs
tty: serial: altera_jtaguart: remove flag from altera_jtaguart_rx_chars()
n_tty: Rename tail to old_tail in n_tty_read()
...
xilinx_uartps .start_tx() clears TXEMPTY when enabling TXEMPTY to avoid
any previous TXEVENT event asserting the UART interrupt. This clear
operation is done immediately after filling the TX FIFO.
However, if the bytes inserted by cdns_uart_handle_tx() are consumed by
the UART before the TXEMPTY is cleared, the clear operation eats the new
TXEMPTY event as well, causing cdns_uart_isr() to never receive the
TXEMPTY event. If there are bytes still queued in circbuf, TX will get
stuck as they will never get transferred to FIFO (unless new bytes are
queued to circbuf in which case .start_tx() is called again).
While the racy missed TXEMPTY occurs fairly often with short data
sequences (e.g. write 1 byte), in those cases circbuf is usually empty
so no action on TXEMPTY would have been needed anyway. On the other
hand, longer data sequences make the race much more unlikely as UART
takes longer to consume the TX FIFO. Therefore it is rare for this race
to cause visible issues in general.
Fix the race by clearing the TXEMPTY bit in ISR *before* filling the
FIFO.
The TXEMPTY bit in ISR will only get asserted at the exact moment the
TX FIFO *becomes* empty, so clearing the bit before filling FIFO does
not cause an extra immediate assertion even if the FIFO is initially
empty.
This is hard to reproduce directly on a normal system, but inserting
e.g. udelay(200) after cdns_uart_handle_tx(port), setting 4000000 baud,
and then running "dd if=/dev/zero bs=128 of=/dev/ttyPS0 count=50"
reliably reproduces the issue on my ZynqMP test system unless this fix
is applied.
Fixes: 85baf542d5 ("tty: xuartps: support 64 byte FIFO size")
Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
Link: https://lore.kernel.org/r/20211026102741.2910441-1-anssi.hannula@bitwise.fi
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Commit c8dbdc842d ("serial: xuartps: Rewrite the interrupt handling
logic") reworked the driver interrupt processing but also, without
comment, added an unnecessary workaround for the infamous low_latency
behaviour of tty_flip_buffer_push() which had been removed years
before.
Specifically, since commit a9c3f68f3c ("tty: Fix low_latency BUG"),
tty_flip_buffer_push() always schedules a work item to push data to the
line discipline and there's no need to keep any low_latency hacks around.
Cc: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210421095509.3024-27-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The problems started with the revert (18cc7ac8a2). The
cdns_uart_console.index is statically assigned -1. When the port is
registered, Linux assigns consecutive numbers to it. It turned out that
when using ttyPS1 as console, the index is not updated as we are reusing
the same cdns_uart_console instance for multiple ports. When registering
ttyPS0, it gets updated from -1 to 0, but when registering ttyPS1, it
already is 0 and not updated.
That led to 2ae11c46d5. It assigns the index prior to registering
the uart_driver once. Unfortunately, that ended up breaking the
situation where the probe order does not match the id order. When using
the same device tree for both uboot and linux, it is important that the
serial0 alias points to the console. So some boards reverse those
aliases. This was reported by Jan Kiszka. The proposed fix was reverting
the index assignment and going back to the previous iteration.
However such a reversed assignement (serial0 -> uart1, serial1 -> uart0)
was already partially broken by the revert (18cc7ac8a2). While the
ttyPS device works, the kmsg connection is already broken and kernel
messages go missing. Reverting the id assignment does not fix this.
>From the xilinx_uartps driver pov (after reverting the refactoring
commits), there can be only one console. This manifests in static
variables console_pprt and cdns_uart_console. These variables are not
properly linked and can go out of sync. The cdns_uart_console.index is
important for uart_add_one_port. We call that function for each port -
one of which hopefully is the console. If it isn't, the CON_ENABLED flag
is not set and console_port is cleared. The next cdns_uart_probe call
then tries to register the next port using that same cdns_uart_console.
It is important that console_port and cdns_uart_console (and its index
in particular) stay in sync. The index assignment implemented by
Shubhrajyoti Datta is correct in principle. It just may have to happen a
second time if the first cdns_uart_probe call didn't encounter the
console device. And we shouldn't change the index once the console uart
is registered.
Reported-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Reported-by: Jan Kiszka <jan.kiszka@web.de>
Link: https://lore.kernel.org/linux-serial/f4092727-d8f5-5f91-2c9f-76643aace993@siemens.com/
Fixes: 18cc7ac8a2 ("Revert "serial: uartps: Register own uart console and driver structures"")
Fixes: 2ae11c46d5 ("tty: xilinx_uartps: Fix missing id assignment to the console")
Fixes: 76ed2e1057 ("Revert "tty: xilinx_uartps: Fix missing id assignment to the console"")
Signed-off-by: Helmut Grohne <helmut.grohne@intenta.de>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200713073227.GA3805@laureti-dev
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
