linux-toradex.git/kernel/printk, branch master

Merge branch 'for-7.4-console-registration' into for-linus

2026-10-22T08:22:29+00:00

Merge branch 'for-7.4' into for-linus

2026-10-22T08:21:06+00:00

printk: Postpone kthread startup

2026-10-16T15:07:29+00:00

There have been various bug reports related to SMP systems hanging
on boot. The reports vary but seem to have some overlap with regard
to missed IPI's during SMP setup. The reports also show that
reverting NBCON console usage allows the bugs to disappear.

The NBCON kthreads for console printing are started very early
during boot using early_initcall(). Since these kthreads are
asynchronously enabling/disabling interrupts during early boot, they
may be interfering with early SMP setup on some hardware platforms.

Starting the console printing kthreads later has shown to avoid the
hanging on systems that could previously reproduce the issue.

Postpone kthread starting until after all arch initcalls have
completed.

Reported-by: Derek Barbosa 
Closes: https://lore.kernel.org/linux-rt-users/arPmYPbFLf2EldIl@debarbos-thinkpadt14gen5.rmtusma.csb
Fixes: 76f258bf3f2a ("printk: nbcon: Introduce printer kthreads")
Signed-off-by: John Ogness 
Tested-by: Derek Barbosa 
Link: https://patch.msgid.link/20261016085441.857695-1-john.ogness@linutronix.de
Signed-off-by: Petr Mladek

printk: fix kernel-doc name for nbcon_write_context_is_braille

2026-10-14T13:00:40+00:00

Use the function name in the kerneldoc description.

Fixes: c83e3d291243 ("braille: nbcon: Allow to use a serial console with NBCON API as Braille console")
Signed-off-by: Muhammad Mahdi Amirpour 
Reviewed-by: John Ogness 
Link: https://patch.msgid.link/20261013151300.75966-1-ampr.mhd@gmail.com
Signed-off-by: Petr Mladek

printk: Remove console options before decoding the name

2026-10-02T14:39:35+00:00

This fixes a regression when a console option includes ':'. Commit
7640f1a44eba ("printk: Add match_devname_and_update_preferred_console()")
introduced console=DEVNAME:0.0 hardware style addressing by looking for a
colon. If the colon is part of an option the name is handled as devname
instead of ttyname.

Fix by handling the options first which will add a NULL terminator to the
string. Note that parsing the options first means that also idx parsing
needs changing. Handle the idx parsing by refactoring the code (thanks to
Petr Mladek).

Signed-off-by: David Engraf 
Reviewed-by: Tony Lindgren 
Reviewed-by: Petr Mladek 
Reviewed-by: John Ogness 
Link: https://patch.msgid.link/20260924070153.250783-2-david.engraf@sysgo.com
[pmladek@suse.com: Updated the commit message as suggested by Tony Lindgren]
Signed-off-by: Petr Mladek

braille: nbcon: Allow to use a serial console with NBCON API as Braille console

2026-10-02T08:26:42+00:00

The Braille console is not registered in console_list. Instead, it is
integrated with the virtual terminal (VT) and shows what is displayed
on the terminal. It writes the data using con->write*() callback
of the associated serial console driver.

braille_write() is called from the VT code under console_lock().
The associated serial console driver can be converted to the NBCON API
though. The situation is similar to flushing nbcon consoles in the legacy
loop when some boot consoles are still registered, see
nbcon_legacy_emit_next_record().

But there is a big difference though. braille_write() is not directly
called from the code paths flushing registered consoles. The VT code
expects that braille_write() succeeds. It does not replay the message
when it can't acquire the ownership. As a result, braille_write():

  + must try harder to get the ownership.

  + has to be synchronized only against non-printk serial console
    which depend nbcon_device_try_acquire() using NBCON_PRIO_NORMAL.

Let's look at it from another side and try to simulate the original
locking using the NBCON API:

  1. Take con->device_lock(), aka the port->lock in the legacy serial
     console driver.

  2. Acquire nbcon context to provide some synchronization for a panic()
     context. Use NBCON_PRIO_NORMAL because it contends only with
     nbcon_device_try_acquire() users. Do it in a busy loop. It should
     always succeed when con->device_lock() succeeded because all other
     users do the same. The only exception is when the context get acquired
     by a CPU handling panic.

  3. In panic, disable interrupts and try to acquire the nbcon context.
     Use NBCON_PRIO_PANIC. And try even an unsafe takeover because
     otherwise the Braille console won't see the text shown during panic().
     It is similar to the oops_in_progress/trylock handling in the legacy
     serial console driver.

Finally, avoid the newline prepending logic in the existing serial console
drivers when they are used as a Braille console. As explained above,
the Braille console shows the last modified line on the terminal (VT).
braille_write() is called when single characters are added. Most
messages are not ended by newline. Anyway, the VT code does not have
logic to reply partially printed messages.

Fixes: 13189fa73afa ("printk: nbcon: Rely on kthreads for normal operation")
Reviewed-by: John Ogness 
[pmladek@suse.com: Remove white space changes in braille_register_console(). Typo fix.]
Link: https://patch.msgid.link/20261001140727.124398-2-pmladek@suse.com
Signed-off-by: Petr Mladek

printk: increase the ring buffer for more than 16 CPUs by default

2026-09-29T14:52:45+00:00

The default LOG_BUF_SHIFT is 17, which means 128 KB, and
LOG_CPU_MAX_BUF_SHIFT is 12, which means 4 KB per CPU.

By default the ring buffer is increased when
(num_possible_cpus() - 1) * 4 KB > 64 KB, which requires more than 17
CPUs.

Remove the explicit subtraction of one, so the ring buffer is increased
for more than 16 CPUs, which is a power of two. Also fix the outdated
comment.

Suggested-by: Petr Mladek 
Signed-off-by: Sang-Heon Jeon 
Reviewed-by: John Ogness 
Reviewed-by: Petr Mladek 
Link: https://patch.msgid.link/20260927091756.50831-1-ekffu200098@gmail.com
Signed-off-by: Petr Mladek

printk_ringbuffer: Avoid needless read of prb_desc

2026-09-29T14:50:37+00:00

Since commit f244b4dc53e5 ("printk: ringbuffer: Improve prb_next_seq()
performance"), desc_read() allows @desc_out to be NULL. We can drop the
local `desc` variable in desc_reopen_last() and prb_first_seq(). Also
update the comment for desc_read().

v1->v2:
Update the comment suggested by John.

Signed-off-by: Wang Wensheng 
Reviewed-by: Petr Mladek 
Reviewed-by: John Ogness 
Link: https://patch.msgid.link/20260926094502.251204-1-wsw9603@163.com
Signed-off-by: Petr Mladek

printk: Use two irq_works instead per-CPU

2026-09-29T14:06:20+00:00

In commit b845b517b5e37 ("printk: robustify printk") initially got its
delayed wake up which is today implemented via the irq_work. Back then
it was a variable which was assigned to 1 if a pending wake up was
waiting. This variable was checked on each timer tick. Therefore it
makes sense to assign a per-CPU variable with this task to avoid cache
line bouncing when each CPU reads the variable on each timer tick
simultaneously.

Today we have a irq_work which is enqueued onto a list and handled if it
has work items assigned. This list is already per-CPU.

We could replace the per-CPU irq_work and the per-CPU printk_pending with
two irq_work structs: One for PRINTK_PENDING_WAKEUP and the other for
PRINTK_PENDING_OUTPUT.
While unrolling the conditions in __wake_up_klogd() it becomes obvious
that PRINTK_PENDING_WAKEUP is always passed as an argument but never
checked. The return value wq_has_sleeper() of does not really matter
it's sole purpose is to enforce the needed memory barrier.

Redo the irq_work by:
- Use one irq_work (pending_wakeup_work) for klogd wakes. Schedule it
  only if there is a sleeper waiting.
- Use one irq_work (&pending_output_work) for output printing. Schedule
  it only if PRINTK_PENDING_OUTPUT passed.
- Drop unused PRINTK_PENDING_WAKEUP.
- Remove the preempt_disable() section. Its purpose was to ensure that
  printk_pending and wake_up_klogd_work is accessed from the same CPU.

Worst case is defer_console_output() where two irq_work are scheduled but
those get processed one after the other during the HZ tick so it
shouldn't get worse.

Signed-off-by: Sebastian Andrzej Siewior 
Reviewed-by: Petr Mladek 
Reviewed-by: John Ogness 
Link: https://patch.msgid.link/20260914143412.1sMcp89V@linutronix.de
Signed-off-by: Petr Mladek

Merge branch 'for-7.4-trivial' into for-linus

2026-09-09T07:52:21+00:00