This reverts commit 09c5ba0aa2fcfdadb17d045c3ee6f86d69270df7. This reverts commit b87f02307d3cfbda768520f0687c51ca77e14fc3. The testing of 5.19 release candidates revealed missing synchronization between early and regular console functionality. It would be possible to start the console kthreads later as a workaround. But it is clear that console lock serialized console drivers between each other. It opens a big area of possible problems that were not considered by people involved in the development and review. printk() is crucial for debugging kernel issues and console output is very important part of it. The number of consoles is huge and a proper review would take some time. As a result it need to be reverted for 5.19. Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220623145157.21938-6-pmladek@suse.com
This reverts commit 8e274732115f63c1d09136284431b3555bd5cc56. The testing of 5.19 release candidates revealed missing synchronization between early and regular console functionality. It would be possible to start the console kthreads later as a workaround. But it is clear that console lock serialized console drivers between each other. It opens a big area of possible problems that were not considered by people involved in the development and review. printk() is crucial for debugging kernel issues and console output is very important part of it. The number of consoles is huge and a proper review would take some time. As a result it need to be reverted for 5.19. Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220623145157.21938-5-pmladek@suse.com
Currently threaded console printers synchronize against each
other using console_lock(). However, different console drivers
are unrelated and do not require any synchronization between
each other. Removing the synchronization between the threaded
console printers will allow each console to print at its own
speed.
But the threaded consoles printers do still need to synchronize
against console_lock() callers. Introduce a per-console mutex
and a new console boolean field @blocked to provide this
synchronization.
console_lock() is modified so that it must acquire the mutex
of each console in order to set the @blocked field. Console
printing threads will acquire their mutex while printing a
record. If @blocked was set, the thread will go back to sleep
instead of printing.
The reason for the @blocked boolean field is so that
console_lock() callers do not need to acquire multiple console
mutexes simultaneously, which would introduce unnecessary
complexity due to nested mutex locking. Also, a new field
was chosen instead of adding a new @flags value so that the
blocked status could be checked without concern of reading
inconsistent values due to @flags updates from other contexts.
Threaded console printers also need to synchronize against
console_trylock() callers. Since console_trylock() may be
called from any context, the per-console mutex cannot be used
for this synchronization. (mutex_trylock() cannot be called
from atomic contexts.) Introduce a global atomic counter to
identify if any threaded printers are active. The threaded
printers will also check the atomic counter to identify if the
console has been locked by another task via console_trylock().
Note that @console_sem is still used to provide synchronization
between console_lock() and console_trylock() callers.
A locking overview for console_lock(), console_trylock(), and the
threaded printers is as follows (pseudo code):
console_lock()
{
down(&console_sem);
for_each_console(con) {
mutex_lock(&con->lock);
con->blocked = true;
mutex_unlock(&con->lock);
}
/* console_lock acquired */
}
console_trylock()
{
if (down_trylock(&console_sem) == 0) {
if (atomic_cmpxchg(&console_kthreads_active, 0, -1) == 0) {
/* console_lock acquired */
}
}
}
threaded_printer()
{
mutex_lock(&con->lock);
if (!con->blocked) {
/* console_lock() callers blocked */
if (atomic_inc_unless_negative(&console_kthreads_active)) {
/* console_trylock() callers blocked */
con->write();
atomic_dec(&console_lock_count);
}
}
mutex_unlock(&con->lock);
}
The console owner and waiter logic now only applies between contexts
that have taken the console_lock via console_trylock(). Threaded
printers never take the console_lock, so they do not have a
console_lock to handover. Tasks that have used console_lock() will
block the threaded printers using a mutex and if the console_lock
is handed over to an atomic context, it would be unable to unblock
the threaded printers. However, the console_trylock() case is
really the only scenario that is interesting for handovers anyway.
@panic_console_dropped must change to atomic_t since it is no longer
protected exclusively by the console_lock.
Since threaded printers remain asleep if they see that the console
is locked, they now must be explicitly woken in __console_unlock().
This means wake_up_klogd() calls following a console_unlock() are
no longer necessary and are removed.
Also note that threaded printers no longer need to check
@console_suspended. The check for the @blocked field implicitly
covers the suspended console case.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/878rrs6ft7.fsf@jogness.linutronix.de
Create a kthread for each console to perform console printing. During normal operation (@system_state == SYSTEM_RUNNING), the kthread printers are responsible for all printing on their respective consoles. During non-normal operation, console printing is done as it has been: within the context of the printk caller or within irqwork triggered by the printk caller, referred to as direct printing. Since threaded console printers are responsible for all printing during normal operation, this also includes messages generated via deferred printk calls. If direct printing is in effect during a deferred printk call, the queued irqwork will perform the direct printing. To make it clear that this is the only time that the irqwork will perform direct printing, rename the flag PRINTK_PENDING_OUTPUT to PRINTK_PENDING_DIRECT_OUTPUT. Threaded console printers synchronize against each other and against console lockers by taking the console lock for each message that is printed. Note that the kthread printers do not care about direct printing. They will always try to print if new records are available. They can be blocked by direct printing, but will be woken again once direct printing is finished. Console unregistration is a bit tricky because the associated kthread printer cannot be stopped while the console lock is held. A policy is implemented that states: whichever task clears con->thread (under the console lock) is responsible for stopping the kthread. unregister_console() will clear con->thread while the console lock is held and then stop the kthread after releasing the console lock. For consoles that have implemented the exit() callback, the kthread is stopped before exit() is called. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220421212250.565456-14-john.ogness@linutronix.de
Refactor/rework printing logic in order to prepare for moving to threaded console printing. - Move @console_seq into struct console so that the current "position" of each console can be tracked individually. - Move @console_dropped into struct console so that the current drop count of each console can be tracked individually. - Modify printing logic so that each console independently loads, prepares, and prints its next record. - Remove exclusive_console logic. Since console positions are handled independently, replaying past records occurs naturally. - Update the comments explaining why preemption is disabled while printing from printk() context. With these changes, there is a change in behavior: the console replaying the log (formerly exclusive console) will no longer block other consoles. New messages appear on the other consoles while the newly added console is still replaying. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20220421212250.565456-10-john.ogness@linutronix.de
The "nomodeset" kernel cmdline parameter is handled by the vgacon driver but the exported vgacon_text_force() symbol is only used by DRM drivers. It makes much more sense for the parameter logic to be in the subsystem of the drivers that are making use of it. Let's move the vgacon_text_force() function and related logic to the DRM subsystem. While doing that, rename it to drm_firmware_drivers_only() and make it return true if "nomodeset" was used and false otherwise. This is a better description of the condition that the drivers are testing for. Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com> Acked-by: Thomas Zimmermann <tzimmermann@suse.de> Acked-by: Jani Nikula <jani.nikula@intel.com> Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Link: https://patchwork.freedesktop.org/patch/msgid/20211112133230.1595307-4-javierm@redhat.com
Since commit edc6afc54968 ("tty: switch to ktermios and new framework")
termios speed is no longer stored only in c_cflag member but also in new
additional c_ispeed and c_ospeed members. If BOTHER flag is set in c_cflag
then termios speed is stored only in these new members.
Therefore to correctly restore termios speed it is required to store also
ispeed and ospeed members, not only cflag member.
In case only cflag member with BOTHER flag is restored then functions
tty_termios_baud_rate() and tty_termios_input_baud_rate() returns baudrate
stored in c_ospeed / c_ispeed member, which is zero as it was not restored
too. If reported baudrate is invalid (e.g. zero) then serial core functions
report fallback baudrate value 9600. So it means that in this case original
baudrate is lost and kernel changes it to value 9600.
Simple reproducer of this issue is to boot kernel with following command
line argument: "console=ttyXXX,86400" (where ttyXXX is the device name).
For speed 86400 there is no Bnnn constant and therefore kernel has to
represent this speed via BOTHER c_cflag. Which means that speed is stored
only in c_ospeed and c_ispeed members, not in c_cflag anymore.
If bootloader correctly configures serial device to speed 86400 then kernel
prints boot log to early console at speed speed 86400 without any issue.
But after kernel starts initializing real console device ttyXXX then speed
is changed to fallback value 9600 because information about speed was lost.
This patch fixes above issue by storing and restoring also ispeed and
ospeed members, which are required for BOTHER flag.
Fixes: edc6afc54968 ("[PATCH] tty: switch to ktermios and new framework")
Cc: stable@vger.kernel.org
Signed-off-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20211002130900.9518-1-pali@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This reverts commit 757055ae8dedf5333af17b3b5b4b70ba9bc9da4e.
The commit caused that ttynull was used as the default console
on several systems[1][2][3]. As a result, the console was
blank even when a better alternative existed.
It happened when there was no console configured
on the command line and ttynull_init() was the first initcall
calling register_console().
Or it happened when /dev/ did not exist when console_on_rootfs()
was called. It was not able to open /dev/console even though
a console driver was registered. It tried to add ttynull console
but it obviously did not help. But ttynull became the preferred
console and was used by /dev/console when it was available later.
The commit tried to fix a historical problem that have been there
for ages. The primary motivation was the commit 3cffa06aeef7ece30f6
("printk/console: Allow to disable console output by using console=""
or console=null"). It provided a clean solution for a workaround
that was widely used and worked only by chance.
This revert causes that the console="" or console=null command line
options will again work only by chance. These options will cause that
a particular console will be preferred and the default (tty) ones
will not get enabled. There will be no console registered at
all. As a result there won't be stdin, stdout, and stderr for
the init process. But it worked exactly this way even before.
The proper solution has to fulfill many conditions:
+ Register ttynull only when explicitly required or as
the ultimate fallback.
+ ttynull should get associated with /dev/console but it must
not become preferred console when used as a fallback.
Especially, it must still be possible to replace it
by a better console later.
Such a change requires clean up of the register_console() code.
Otherwise, it would be even harder to follow. Especially, the use
of has_preferred_console and CON_CONSDEV flag is tricky. The clean
up is risky. The ordering of consoles is not well defined. And
any changes tend to break existing user settings.
Do the revert at the least risky solution for now.
[1] https://lore.kernel.org/linux-kselftest/20201221144302.GR4077@smile.fi.intel.com/
[2] https://lore.kernel.org/lkml/d2a3b3c0-e548-7dd1-730f-59bc5c04e191@synopsys.com/
[3] https://patchwork.ozlabs.org/project/linux-um/patch/20210105120128.10854-1-thomas@m3y3r.de/
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reported-by: Vineet Gupta <vgupta@synopsys.com>
Reported-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull printk updates from Petr Mladek: - Finally allow parallel writes and reads into/from the lockless ringbuffer. But it is not a complete solution. Readers are still serialized against each other. And nested writes are still prevented by printk_safe per-CPU buffers. - Use ttynull as the ultimate fallback for /dev/console. - Officially allow disabling console output by using console="" or console=null - A few code cleanups * tag 'printk-for-5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: printk: remove logbuf_lock writer-protection of ringbuffer printk: inline log_output(),log_store() in vprintk_store() printk: remove obsolete dead assignment printk/console: Allow to disable console output by using console="" or console=null init/console: Use ttynull as a fallback when there is no console printk: ringbuffer: Reference text_data_ring directly in callees.
stdin, stdout, and stderr standard I/O stream are created for the init
process. They are not available when there is no console registered
for /dev/console. It might lead to a crash when the init process
tries to use them, see the commit 48021f98130880dd742 ("printk: handle
blank console arguments passed in.").
Normally, ttySX and ttyX consoles are used as a fallback when no consoles
are defined via the command line, device tree, or SPCR. But there
will be no console registered when an invalid console name is configured
or when the configured consoles do not exist on the system.
Users even try to avoid the console intentionally, for example,
by using console="" or console=null. It is used on production
systems where the serial port or terminal are not visible to
users. Pushing messages to these consoles would just unnecessary
slowdown the system.
Make sure that stdin, stdout, stderr, and /dev/console are always
available by a fallback to the existing ttynull driver. It has
been implemented for exactly this purpose but it was used only
when explicitly configured.
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20201111135450.11214-2-pmladek@suse.com