kernel/linux.git/drivers/tty/tty_io.c, branch v7.1-rc5

tty: tty_port: add workqueue to flip TTY buffer

2026-03-12T14:26:29+00:00

On the embedded platform, certain critical data, such as IMU data, is transmitted through UART. The tty_flip_buffer_push() interface in the TTY layer uses system_dfl_wq to handle the flipping of the TTY buffer. Although the unbound workqueue can create new threads on demand and wake up the kworker thread on an idle CPU, it may be preempted by real-time tasks or other high-prio tasks. flush_to_ldisc() needs to wake up the relevant data handle thread. When executing __wake_up_common_lock(), it calls spin_lock_irqsave(), which does not disable preemption but disables migration in RT-Linux. This prevents the kworker thread from being migrated to other cores by CPU's balancing logic, resulting in long delays. The call trace is as follows: __wake_up_common_lock __wake_up ep_poll_callback __wake_up_common __wake_up_common_lock __wake_up n_tty_receive_buf_common n_tty_receive_buf2 tty_ldisc_receive_buf tty_port_default_receive_buf flush_to_ldisc In our system, the processing interval for each frame of IMU data transmitted via UART can experience significant jitter due to this issue. Instead of the expected 10 to 15 ms frame processing interval, we see spikes up to 30 to 35 ms. Moreover, in just one or two hours, there can be 2 to 3 occurrences of such high jitter, which is quite frequent. This jitter exceeds the software's tolerable limit of 20 ms. Introduce flip_wq in tty_port which can be set by tty_port_link_wq() or as default linked to default workqueue allocated when tty_register_driver(). The default workqueue is allocated with flag WQ_SYSFS, so that cpumask and nice can be set dynamically. The execution timing of tty_port_link_wq() is not clearly restricted. The newly added function tty_port_link_driver_wq() checks whether the flip_wq of the tty_port has already been assigned when linking the default tty_driver's workqueue to the port. After the user has set a custom workqueue for a certain tty_port using tty_port_link_wq(), the system will only use this custom workqueue, even if tty_driver does not have %TTY_DRIVER_NO_WORKQUEUE flag. When tty_port register device, flip_wq link operation is done by tty_port_link_driver_wq(), but for in-memory devices the link operation cannot cover all the cases. Although tty_port_install() is dedicated for in-memory devices lik PTY to link port allocated on demand, the logic of tty_port_install() is so simple that people may not call it, vc_cons[0].d->port is one such case. We check the buf.flip_wq when flip TTY buffer, if buf.flip_wq of TTY port is NULL, use system_dfl_wq as a backup. To avoid naming conflict of the default tty_driver's workqueue, using '"%s-%s", driver->name, driver->driver_name' as the workqueue name. In cases where driver_name is not specified and therefore is NULL, the workqueue is not created. Drivers that do not define driver_name are potentially in-memory devices like vty, which generally do not require special workqueue settings. Even with the combination of name and driver_name, the workqueue names can still be duplicated, as many tty serial drivers use "ttyS" as dev_name and "serial" as driver_name. I modified the conflicting driver_name of these drivers by appending a suffix of _xx based on the corresponding .c file. If this modification is not made, it could not only lead to duplicate workqueue names but also result in duplicate entries for the /proc/tty/driver/ nodes. Introduce %TTY_DRIVER_NO_WORKQUEUE flag meaning not to create the default single tty_driver workqueue. Two reasons why need to introduce the %TTY_DRIVER_NO_WORKQUEUE flag: 1. If the WQ_SYSFS parameter is enabled, workqueue_sysfs_register() will fail when trying to create a workqueue with the same name. The pty is an example of this; if both CONFIG_LEGACY_PTYS and CONFIG_UNIX98_PTYS are enabled, the call to tty_register_driver() in unix98_pty_init() will fail. 2. Different TTY ports may be used for different tasks, which may require separate core binding control via workqueues. In this case, the workqueue created by default in the TTY driver is unnecessary. Enabling this flag prevents the creation of this redundant workqueue. After applying this patch, we can set the related UART TTY flip buffer workqueue by sysfs. We set the cpumask to CPU cores associated with the IMU tasks, and set the nice to -20. Testing has shown significant improvement in the previously described issue, with almost no stuttering occurring anymore. Tested-by: Tommaso Merciai Tested-by: Marek Szyprowski Signed-off-by: Xin Zhao Link: https://patch.msgid.link/20260213085039.3274704-1-jackzxcui1989@163.com Signed-off-by: Greg Kroah-Hartman

Convert more 'alloc_obj' cases to default GFP_KERNEL arguments

2026-02-22T04:03:00+00:00

This converts some of the visually simpler cases that have been split over multiple lines. I only did the ones that are easy to verify the resulting diff by having just that final GFP_KERNEL argument on the next line. Somebody should probably do a proper coccinelle script for this, but for me the trivial script actually resulted in an assertion failure in the middle of the script. I probably had made it a bit _too_ trivial. So after fighting that far a while I decided to just do some of the syntactically simpler cases with variations of the previous 'sed' scripts. The more syntactically complex multi-line cases would mostly really want whitespace cleanup anyway. Signed-off-by: Linus Torvalds

Convert 'alloc_obj' family to use the new default GFP_KERNEL argument

2026-02-22T01:09:51+00:00

This was done entirely with mindless brute force, using git grep -l '\

treewide: Replace kmalloc with kmalloc_obj for non-scalar types

2026-02-21T09:02:28+00:00

This is the result of running the Coccinelle script from scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to avoid scalar types (which need careful case-by-case checking), and instead replace kmalloc-family calls that allocate struct or union object instances: Single allocations: kmalloc(sizeof(TYPE), ...) are replaced with: kmalloc_obj(TYPE, ...) Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...) are replaced with: kmalloc_objs(TYPE, COUNT, ...) Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...) are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...) (where TYPE may also be *VAR) The resulting allocations no longer return "void *", instead returning "TYPE *". Signed-off-by: Kees Cook

tty: use lock guard()s in tty_io

2025-04-25T11:46:31+00:00

guard()s and scoped_guard()s express more clearly what is protected by locks. And also makes the code cleaner as it can return immediately in case of short returns. Signed-off-by: Jiri Slaby (SUSE) Link: https://lore.kernel.org/r/20250425111315.1036184-3-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

tty: tty_driver: document both {,__}tty_alloc_driver() properly

2025-03-20T15:00:51+00:00

__tty_alloc_driver()'s kernel-doc needed some care: describe the return value using the standard "Returns:", and use the new enum tty_driver_flag for @flags. Then, the tty_alloc_driver() macro was undocumented, but referenced many times in the docs. Copy the docs from the above (except the @owner parameter, obviously). Signed-off-by: Jiri Slaby (SUSE) Link: https://lore.kernel.org/r/20250317070046.24386-15-jirislaby@kernel.org Signed-off-by: Greg Kroah-Hartman

Merge tag 'tty-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty

2025-01-28T17:55:04+00:00

Pull tty / serial driver updates from Greg KH: "Here is the tty/serial driver set of changes for 6.14-rc1. Nothing major in here, it was delayed a bit due to a regression found in linux-next which has now been reverted and verified that it is fixed. Other than the reverts, highlights include: - 8250 work to get the nbcon mode working (partially reverted) - altera_jtaguart minor fixes - fsl_lpuart minor updates - sh-sci driver minor updatesa - other tiny driver updates and cleanups All of these have been in linux-next for a while, and now with no reports of problems (thanks to the reverts)" * tag 'tty-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (44 commits) Revert "serial: 8250: Switch to nbcon console" Revert "serial: 8250: Revert "drop lockdep annotation from serial8250_clear_IER()"" serial: sh-sci: Increment the runtime usage counter for the earlycon device serial: sh-sci: Clean sci_ports[0] after at earlycon exit serial: sh-sci: Do not probe the serial port if its slot in sci_ports[] is in use serial: sh-sci: Move runtime PM enable to sci_probe_single() serial: sh-sci: Drop __initdata macro for port_cfg serial: kgdb_nmi: Remove unused knock code tty: Permit some TIOCL_SETSEL modes without CAP_SYS_ADMIN tty: xilinx_uartps: split sysrq handling serial: 8250: Revert "drop lockdep annotation from serial8250_clear_IER()" serial: 8250: Switch to nbcon console serial: 8250: Provide flag for IER toggling for RS485 serial: 8250: Use high-level writing function for FIFO serial: 8250: Use frame time to determine timeout serial: 8250: Adjust the timeout for FIFO mode tty: atmel_serial: Use of_property_present() for non-boolean properties serial: sc16is7xx: Add polling mode if no IRQ pin is available dt-bindings: serial: sc16is7xx: Add description for polling mode tty: serial: atmel: make it selectable for ARCH_LAN969X ...

drivers: remove get_task_comm() and print task comm directly

2025-01-13T04:21:16+00:00

Since task->comm is guaranteed to be NUL-terminated, we can print it directly without the need to copy it into a separate buffer. This simplifies the code and avoids unnecessary operations. Link: https://lkml.kernel.org/r/20241219023452.69907-6-laoar.shao@gmail.com Signed-off-by: Yafang Shao Reviewed-by: Jiri Slaby (For tty) Reviewed-by: Lyude Paul (For nouveau) Cc: Oded Gabbay Cc: Jani Nikula Cc: Rodrigo Vivi Cc: Joonas Lahtinen Cc: Tvrtko Ursulin Cc: David Airlie Cc: Simona Vetter Cc: Karol Herbst Cc: Lyude Paul Cc: Danilo Krummrich Cc: Greg Kroah-Hartman Cc: Jiri Slaby Cc: "André Almeida" Cc: Andy Shevchenko Cc: Borislav Petkov (AMD) Cc: Darren Hart Cc: Dave Hansen Cc: Davidlohr Bueso Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: James Morris Cc: Johannes Berg Cc: Kalle Valo Cc: Kees Cook Cc: Linus Torvalds Cc: Paul Moore Cc: Peter Zijlstra Cc: Petr Mladek Cc: "Serge E. Hallyn" Cc: Thomas Gleixner Cc: Vineet Gupta Signed-off-by: Andrew Morton

tty: Make sysctl table const

2024-12-14T14:40:27+00:00

Since commit 7abc9b53bd51 ("sysctl: allow registration of const struct ctl_table"), the sysctl registration API allows for struct ctl_table to be in read-only memory. Move tty_table to be declared at build time, instead of having to be dynamically allocated at boot time. Cc: Thomas Weißschuh Suggested-by: Thomas Weißschuh Signed-off-by: Ricardo B. Marliere Link: https://lore.kernel.org/r/20241213-sysctl_const-tty-v1-1-2e2bcec77f85@suse.com Signed-off-by: Greg Kroah-Hartman

tty: ldsic: fix tty_ldisc_autoload sysctl's proc_handler

2024-11-13T14:12:19+00:00

Commit 7c0cca7c847e ("tty: ldisc: add sysctl to prevent autoloading of ldiscs") introduces the tty_ldisc_autoload sysctl with the wrong proc_handler. .extra1 and .extra2 parameters are set to avoid other values thant SYSCTL_ZERO or SYSCTL_ONE to be set but proc_dointvec do not uses them. This commit fixes this by using proc_dointvec_minmax instead of proc_dointvec. Fixes: 7c0cca7c847e ("tty: ldisc: add sysctl to prevent autoloading of ldiscs") Cc: stable Signed-off-by: Nicolas Bouchinet Reviewed-by: Lin Feng Reviewed-by: Jiri Slaby Link: https://lore.kernel.org/r/20241112131357.49582-4-nicolas.bouchinet@clip-os.org Signed-off-by: Greg Kroah-Hartman