linux-stable.git/kernel/printk/nbcon.c, branch linux-rolling-lts

printk: Allow printk_trigger_flush() to flush all types

2026-01-02T11:57:09+00:00

commit d01ff281bd9b1bfeac9ab98ec8a9ee41da900d5e upstream.

Currently printk_trigger_flush() only triggers legacy offloaded
flushing, even if that may not be the appropriate method to flush
for currently registered consoles. (The function predates the
NBCON consoles.)

Since commit 6690d6b52726 ("printk: Add helper for flush type
logic") there is printk_get_console_flush_type(), which also
considers NBCON consoles and reports all the methods of flushing
appropriate based on the system state and consoles available.

Update printk_trigger_flush() to use
printk_get_console_flush_type() to appropriately flush registered
consoles.

Suggested-by: Petr Mladek 
Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/stable/20251113160351.113031-2-john.ogness%40linutronix.de
Tested-by: Sherry Sun 
Link: https://patch.msgid.link/20251113160351.113031-2-john.ogness@linutronix.de
Signed-off-by: Petr Mladek 
Signed-off-by: Greg Kroah-Hartman

printk: Avoid scheduling irq_work on suspend

2026-01-02T11:57:06+00:00

commit 26873e3e7f0cb26c45e6ad63656f9fe36b2aa31b upstream.

Allowing irq_work to be scheduled while trying to suspend has shown
to cause problems as some architectures interpret the pending
interrupts as a reason to not suspend. This became a problem for
printk() with the introduction of NBCON consoles. With every
printk() call, NBCON console printing kthreads are woken by queueing
irq_work. This means that irq_work continues to be queued due to
printk() calls late in the suspend procedure.

Avoid this problem by preventing printk() from queueing irq_work
once console suspending has begun. This applies to triggering NBCON
and legacy deferred printing as well as klogd waiters.

Since triggering of NBCON threaded printing relies on irq_work, the
pr_flush() within console_suspend_all() is used to perform the final
flushing before suspending consoles and blocking irq_work queueing.
NBCON consoles that are not suspended (due to the usage of the
"no_console_suspend" boot argument) transition to atomic flushing.

Introduce a new global variable @console_irqwork_blocked to flag
when irq_work queueing is to be avoided. The flag is used by
printk_get_console_flush_type() to avoid allowing deferred printing
and switch NBCON consoles to atomic flushing. It is also used by
vprintk_emit() to avoid klogd waking.

Add WARN_ON_ONCE(console_irqwork_blocked) to the irq_work queuing
functions to catch any code that attempts to queue printk irq_work
during the suspending/resuming procedure.

Cc: stable@vger.kernel.org # 6.13.x because no drivers in 6.12.x
Fixes: 6b93bb41f6ea ("printk: Add non-BKL (nbcon) console basic infrastructure")
Closes: https://lore.kernel.org/lkml/DB9PR04MB8429E7DDF2D93C2695DE401D92C4A@DB9PR04MB8429.eurprd04.prod.outlook.com
Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Tested-by: Sherry Sun 
Link: https://patch.msgid.link/20251113160351.113031-3-john.ogness@linutronix.de
Signed-off-by: Petr Mladek 
Signed-off-by: Greg Kroah-Hartman

panic: use angle-bracket include for panic.h

2025-09-14T00:32:54+00:00

Replace quoted includes of panic.h with `#include ` for
consistency across the kernel.

Link: https://lkml.kernel.org/r/20250829051312.33773-1-wangjinchao600@gmail.com
Signed-off-by: Jinchao Wang 
Reviewed-by: John Ogness 
Reviewed-by: Petr Mladek 
Cc: Qianqiang Liu 
Cc: Sergey Senozhatsky 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton

panic/printk: replace other_cpu_in_panic() with panic_on_other_cpu()

2025-09-14T00:32:52+00:00

The helper other_cpu_in_panic() duplicated logic already provided by
panic_on_other_cpu().

Remove other_cpu_in_panic() and update all users to call
panic_on_other_cpu() instead.

This removes redundant code and makes panic handling consistent.

Link: https://lkml.kernel.org/r/20250825022947.1596226-9-wangjinchao600@gmail.com
Signed-off-by: Jinchao Wang 
Cc: Anna Schumaker 
Cc: Baoquan He 
Cc: "Darrick J. Wong" 
Cc: Dave Young 
Cc: Doug Anderson 
Cc: "Guilherme G. Piccoli" 
Cc: Helge Deller 
Cc: Ingo Molnar 
Cc: Jason Gunthorpe 
Cc: Joanthan Cameron 
Cc: Joel Granados 
Cc: John Ogness 
Cc: Kees Cook 
Cc: Li Huafei 
Cc: "Luck, Tony" 
Cc: Luo Gengkun 
Cc: Max Kellermann 
Cc: Nam Cao 
Cc: oushixiong 
Cc: Petr Mladek 
Cc: Qianqiang Liu 
Cc: Sergey Senozhatsky 
Cc: Sohil Mehta 
Cc: Steven Rostedt 
Cc: Tejun Heo 
Cc: Thomas Gleinxer 
Cc: Thomas Zimemrmann 
Cc: Thorsten Blum 
Cc: Ville Syrjala 
Cc: Vivek Goyal 
Cc: Yicong Yang 
Cc: Yunhui Cui 
Cc: Yury Norov (NVIDIA) 
Signed-off-by: Andrew Morton

panic/printk: replace this_cpu_in_panic() with panic_on_this_cpu()

2025-09-14T00:32:52+00:00

The helper this_cpu_in_panic() duplicated logic already provided by
panic_on_this_cpu().

Remove this_cpu_in_panic() and switch all users to panic_on_this_cpu().

This simplifies the code and avoids having two helpers for the same check.

Link: https://lkml.kernel.org/r/20250825022947.1596226-8-wangjinchao600@gmail.com
Signed-off-by: Jinchao Wang 
Cc: Anna Schumaker 
Cc: Baoquan He 
Cc: "Darrick J. Wong" 
Cc: Dave Young 
Cc: Doug Anderson 
Cc: "Guilherme G. Piccoli" 
Cc: Helge Deller 
Cc: Ingo Molnar 
Cc: Jason Gunthorpe 
Cc: Joanthan Cameron 
Cc: Joel Granados 
Cc: John Ogness 
Cc: Kees Cook 
Cc: Li Huafei 
Cc: "Luck, Tony" 
Cc: Luo Gengkun 
Cc: Max Kellermann 
Cc: Nam Cao 
Cc: oushixiong 
Cc: Petr Mladek 
Cc: Qianqiang Liu 
Cc: Sergey Senozhatsky 
Cc: Sohil Mehta 
Cc: Steven Rostedt 
Cc: Tejun Heo 
Cc: Thomas Gleinxer 
Cc: Thomas Zimemrmann 
Cc: Thorsten Blum 
Cc: Ville Syrjala 
Cc: Vivek Goyal 
Cc: Yicong Yang 
Cc: Yunhui Cui 
Cc: Yury Norov (NVIDIA) 
Signed-off-by: Andrew Morton

printk/nbcon: use panic_on_this_cpu() helper

2025-09-14T00:32:52+00:00

nbcon_context_try_acquire() compared panic_cpu directly with
smp_processor_id().  This open-coded check is now provided by
panic_on_this_cpu().

Switch to panic_on_this_cpu() to simplify the code and improve readability.

Link: https://lkml.kernel.org/r/20250825022947.1596226-7-wangjinchao600@gmail.com
Signed-off-by: Jinchao Wang 
Cc: Anna Schumaker 
Cc: Baoquan He 
Cc: "Darrick J. Wong" 
Cc: Dave Young 
Cc: Doug Anderson 
Cc: "Guilherme G. Piccoli" 
Cc: Helge Deller 
Cc: Ingo Molnar 
Cc: Jason Gunthorpe 
Cc: Joanthan Cameron 
Cc: Joel Granados 
Cc: John Ogness 
Cc: Kees Cook 
Cc: Li Huafei 
Cc: "Luck, Tony" 
Cc: Luo Gengkun 
Cc: Max Kellermann 
Cc: Nam Cao 
Cc: oushixiong 
Cc: Petr Mladek 
Cc: Qianqiang Liu 
Cc: Sergey Senozhatsky 
Cc: Sohil Mehta 
Cc: Steven Rostedt 
Cc: Tejun Heo 
Cc: Thomas Gleinxer 
Cc: Thomas Zimemrmann 
Cc: Thorsten Blum 
Cc: Ville Syrjala 
Cc: Vivek Goyal 
Cc: Yicong Yang 
Cc: Yunhui Cui 
Cc: Yury Norov (NVIDIA) 
Signed-off-by: Andrew Morton

Merge branch 'rework/fixes' into for-linus

2025-08-04T12:18:01+00:00

printk: nbcon: Allow reacquire during panic

2025-06-17T10:10:29+00:00

If a console printer is interrupted during panic, it will never
be able to reacquire ownership in order to perform and cleanup.
That in itself is not a problem, since the non-panic CPU will
simply quiesce in an endless loop within nbcon_reacquire_nobuf().

However, in this state, platforms that do not support a true NMI
to interrupt the quiesced CPU will not be able to shutdown that
CPU from within panic(). This then causes problems for such as
being unable to load and run a kdump kernel.

Fix this by allowing non-panic CPUs to reacquire ownership using
a direct acquire. Then the non-panic CPUs can successfullyl exit
the nbcon_reacquire_nobuf() loop and the console driver can
perform any necessary cleanup. But more importantly, the CPU is
no longer quiesced and is free to process any interrupts
necessary for panic() to shutdown the CPU.

All other forms of acquire are still not allowed for non-panic
CPUs since it is safer to have them avoid gaining console
ownership that is not strictly necessary.

Reported-by: Michael Kelley 
Closes: https://lore.kernel.org/r/SN6PR02MB4157A4C5E8CB219A75263A17D46DA@SN6PR02MB4157.namprd02.prod.outlook.com
Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Tested-by: Michael Kelley 
Link: https://patch.msgid.link/20250606185549.900611-1-john.ogness@linutronix.de
Signed-off-by: Petr Mladek

printk: Allow to use the printk kthread immediately even for 1st nbcon

2025-06-09T14:44:01+00:00

The kthreads for nbcon consoles are created by nbcon_alloc() at
the beginning of the console registration. But it currently works
only for the 2nd or later nbcon console because the code checks
@printk_kthreads_running.

The kthread for the 1st registered nbcon console is created at the very
end of register_console() by printk_kthreads_check_locked(). As a result,
the entire log is replayed synchronously when the "enabled" message
gets printed. It might block the boot for a long time with a slow serial
console.

Prevent the synchronous flush by creating the kthread even for the 1st
nbcon console when it is safe (kthreads ready and no boot consoles).

Also inform printk() to use the kthread by setting
@printk_kthreads_running. Note that the kthreads already must be
running when it is safe and this is not the 1st nbcon console.

Symmetrically, clear @printk_kthreads_running when the last nbcon
console was unregistered by nbcon_free(). This requires updating
@have_nbcon_console before nbcon_free() gets called.

Note that there is _no_ problem when the 1st nbcon console replaces boot
consoles. In this case, the kthread will be started at the end
of registration after the boot consoles are removed. But the console
does not reply the entire log buffer in this case. Note that
the flag CON_PRINTBUFFER is always cleared when the boot consoles are
removed and vice versa.

Closes: https://lore.kernel.org/r/20250514173514.2117832-1-mcobb@thegoodpenguin.co.uk
Tested-by: Michael Cobb 
Reviewed-by: John Ogness 
Link: https://patch.msgid.link/20250604142045.253301-1-pmladek@suse.com
Signed-off-by: Petr Mladek

printk: nbcon: Assign nice -20 for printing threads

2024-09-04T13:56:33+00:00

It is important that console printing threads are scheduled
shortly after a printk call and with generous runtime budgets.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20240904120536.115780-17-john.ogness@linutronix.de
Signed-off-by: Petr Mladek