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/<driver_name> 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 <tommaso.merciai.xr@bp.renesas.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Xin Zhao <jackzxcui1989@163.com>
Link: https://patch.msgid.link/20260213085039.3274704-1-jackzxcui1989@163.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This was done entirely with mindless brute force, using
git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'
to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.
Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.
For the same reason the 'flex' versions will be done as a separate
conversion.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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 <kees@kernel.org>
Pull tty/serial updates from Greg KH:
"Here is the big set of tty/serial driver changes for 6.19-rc1. Nothing
major at all, just small constant churn to make the tty layer
"cleaner" as well as serial driver updates and even a new test added!
Included in here are:
- More tty/serial cleanups from Jiri
- tty tiocsti test added to hopefully ensure we don't regress in this
area again
- sc16is7xx driver updates
- imx serial driver updates
- 8250 driver updates
- new hardware device ids added
- other minor serial/tty driver cleanups and tweaks
All of these have been in linux-next for a while with no reported
issues"
* tag 'tty-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty: (60 commits)
serial: sh-sci: Fix deadlock during RSCI FIFO overrun error
dt-bindings: serial: rsci: Drop "uart-has-rtscts: false"
LoongArch: dts: Add uart new compatible string
serial: 8250: Add Loongson uart driver support
dt-bindings: serial: 8250: Add Loongson uart compatible
serial: 8250: add driver for KEBA UART
serial: Keep rs485 settings for devices without firmware node
serial: qcom-geni: Enable Serial on SA8255p Qualcomm platforms
serial: qcom-geni: Enable PM runtime for serial driver
serial: sprd: Return -EPROBE_DEFER when uart clock is not ready
tty: serial: samsung: Declare earlycon for Exynos850
serial: icom: Convert PCIBIOS_* return codes to errnos
serial: 8250-of: Fix style issues in 8250_of.c
serial: add support of CPCI cards
serial: mux: Fix kernel doc for mux_poll()
tty: replace use of system_unbound_wq with system_dfl_wq
serial: 8250_platform: simplify IRQF_SHARED handling
serial: 8250: make share_irqs local to 8250_platform
serial: 8250: move skip_txen_test to core
serial: drop SERIAL_8250_DEPRECATED_OPTIONS
...
Use guards in the pty code. This improves readability, makes error
handling easier, and marks locked portions of code explicit. All that
while being sure the lock is unlocked.
pty_set_pktmode() is handled specially -- the conditions are inverted
and return called if conditions unmet. This avoid double nested 'if's.
The variable is renamed to want_pktmode so it is not confused with the
current state of pktmode.
Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Link: https://patch.msgid.link/20251119100140.830761-2-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The FMODE_NONOTIFY_* bits are a 2-bits mode. Open coding manipulation
of those bits is risky. Use an accessor file_set_fsnotify_mode() to
set the mode.
Rename file_set_fsnotify_mode() => file_set_fsnotify_mode_from_watchers()
to make way for the simple accessor name.
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20250203223205.861346-2-amir73il@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
There is a race in pty_write(). pty_write() can be called in parallel
with e.g. ioctl(TIOCSTI) or ioctl(TCXONC) which also inserts chars to
the buffer. Provided, tty_flip_buffer_push() in pty_write() is called
outside the lock, it can commit inconsistent tail. This can lead to out
of bounds writes and other issues. See the Link below.
To fix this, we have to introduce a new helper called
tty_insert_flip_string_and_push_buffer(). It does both
tty_insert_flip_string() and tty_flip_buffer_commit() under the port
lock. It also calls queue_work(), but outside the lock. See
71a174b39f (pty: do tty_flip_buffer_push without port->lock in
pty_write) for the reasons.
Keep the helper internal-only (in drivers' tty.h). It is not intended to
be used widely.
Link: https://seclists.org/oss-sec/2022/q2/155
Fixes: 71a174b39f (pty: do tty_flip_buffer_push without port->lock in pty_write)
Cc: 一只狗 <chennbnbnb@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Suggested-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220707082558.9250-2-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Group the ctrl members under a single struct called ctrl. The new struct
contains 'pgrp', 'session', 'pktstatus', and 'packet'. 'pktstatus' and
'packet' used to be bits in a bitfield. The struct also contains the
lock protecting them to share the same cache line.
Note that commit c545b66c69 (tty: Serialize tcflow() with other tty
flow control changes) added a padding to the original bitfield. It was
for the bitfield to occupy a whole 64b word to avoid interferring stores
on Alpha (cannot we evaporate this arch with weird implications to C
code yet?). But it doesn't work as expected as the padding
(tty_struct::ctrl_unused) is aligned to a 8B boundary too and occupies
some bytes from the next word.
So make it reliable by:
1) setting __aligned of the struct -- that aligns the start, and
2) making 'unsigned long unused[0]' as the last member of the struct --
pads the end.
Add a kerneldoc comment for this grouped members.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/r/20210505091928.22010-14-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Group the flow flags under a single struct called flow. The new struct
contains 'stopped' and 'tco_stopped' bools which used to be bits in a
bitfield. The struct also contains the lock protecting them to
potentially share the same cache line.
Note that commit c545b66c69 (tty: Serialize tcflow() with other tty
flow control changes) added a padding to the original bitfield. It was
for the bitfield to occupy a whole 64b word to avoid interferring stores
on Alpha (cannot we evaporate this arch with weird implications to C
code yet?). But it doesn't work as expected as the padding
(tty_struct::unused) is aligned to a 8B boundary too and occupies some
bytes from the next word.
So make it reliable by:
1) setting __aligned of the struct -- that aligns the start, and
2) making 'unsigned long unused[0]' as the last member of the struct --
pads the end.
This is also the perfect time to start the documentation of tty_struct
where all this lives. So we start by documenting what these bools
actually serve for. And why we do all the alignment dances. Only the few
up-to-date information from the Theodore's comment made it into this new
Kerneldoc comment.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: "Maciej W. Rozycki" <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/20210505091928.22010-13-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This reverts commit 33d4ae9885.
Pierre-Louis writes:
Our SOF/audio CI shows an across-the-board regression when we try v5.12-rc1,
specifically on pause/resume tests with an interactive terminal running 'aplay
-i' commands managed by expect to simulate the user pressing the space bar to
pause/unpause. It turns out the processes are not longer killed and the audio
devices remain busy (see publicly available test results listed below).
git bisect points to commit 33d4ae9885 ("drivers:tty:pty: Fix a race
causing data loss on close"). Reverting the patch fixes the issue on all test
devices.
Further analysis with Corey Minyard points to a problem where a slave tty will
not get a SIGHUP when the master is closed.
So revert this for now:
Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/00154592-c5ee-aaba-956e-b265473b53bc@linux.intel.com
Cc: Corey Minyard <cminyard@mvista.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Mark Brown <broonie@kernel.org>,
Fixes: 33d4ae9885 ("drivers:tty:pty: Fix a race causing data loss on close")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Remove the tty_vhangup() from the pty code and just release the
redirect. The tty_vhangup() results in data loss and data out of order
issues.
If you write to a pty master an immediately close the pty master, the
receiver might get a chunk of data dropped, but then receive some later
data. That's obviously something rather unexpected for a user. It
certainly confused my test program.
It turns out that tty_vhangup() on the slave pty gets called from
pty_close(), and that causes the data on the slave side to be flushed,
but due to races more data can be copied into the slave side's buffer
after that. Consider the following sequence:
thread1 thread2 thread3
------- ------- -------
| |-write data into buffer,
| | n_tty buffer is filled
| | along with other buffers
| |-pty_close(master)
| |--tty_vhangup(slave)
| |---tty_ldisc_hangup()
| |----n_tty_flush_buffer()
| |-----reset_buffer_flags()
|-n_tty_read() |
|--up_read(&tty->termios_rwsem);
| |------down_read(&tty->termios_rwsem)
| |------clear n_tty buffer contents
| |------up_read(&tty->termios_rwsem)
|--tty_buffer_flush_work() |
|--schedules work calling |
| flush_to_ldisc() |
| |-flush_to_ldisc()
| |--receive_buf()
| |---tty_port_default_receive_buf()
| |----tty_ldisc_receive_buf()
| |-----n_tty_receive_buf2()
| |------n_tty_receive_buf_common()
| |-------down_read(&tty->termios_rwsem)
| |-------__receive_buf()
| | copies data into n_tty buffer
| |-------up_read(&tty->termios_rwsem)
|--down_read(&tty->termios_rwsem)
|--copy buffer data to user
>From this sequence, you can see that thread2 writes to the buffer then
only clears the part of the buffer in n_tty. The n_tty receive buffer
code then copies more data into the n_tty buffer.
But part of the vhangup, releasing the redirect, is still required to
avoid issues with consoles running on pty slaves. So do that.
As far as I can tell, that is all that should be required.
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Link: https://lore.kernel.org/r/20201124004902.1398477-3-minyard@acm.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
