printk: nbcon: Assign nice -20 for printing threads

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

Signed-off-by: John Og

printk: nbcon: Assign nice -20 for printing threads

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

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Show replay message on takeover

An emergency or panic context can takeover console ownership
while the current owner was printing a printk message. The
atomic printer will re-print th

printk: nbcon: Show replay message on takeover

An emergency or panic context can takeover console ownership
while the current owner was printing a printk message. The
atomic printer will re-print the message that the previous
owner was printing. However, this can look confusing to the
user and may even seem as though a message was lost.

[3430014.1
[3430014.181123] usb 1-2: Product: USB Audio

Add a new field @nbcon_prev_seq to struct console to track
the sequence number to print that was assigned to the previous
console owner. If this matches the sequence number to print
that the current owner is assigned, then a takeover must have
occurred. In this case, print an additional message to inform
the user that the previous message is being printed again.

[3430014.1
** replaying previous printk message **
[3430014.181123] usb 1-2: Product: USB Audio

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

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printk: nbcon: Rely on kthreads for normal operation

Once the kthread is running and available
(i.e. @printk_kthreads_running is set), the kthread becomes
responsible for flushing any pending messag

printk: nbcon: Rely on kthreads for normal operation

Once the kthread is running and available
(i.e. @printk_kthreads_running is set), the kthread becomes
responsible for flushing any pending messages which are added
in NBCON_PRIO_NORMAL context. Namely the legacy
console_flush_all() and device_release() no longer flush the
console. And nbcon_atomic_flush_pending() used by
nbcon_cpu_emergency_exit() no longer flushes messages added
after the emergency messages.

The console context is safe when used by the kthread only when
one of the following conditions are true:

1. Other caller acquires the console context with
NBCON_PRIO_NORMAL with preemption disabled. It will
release the context before rescheduling.

2. Other caller acquires the console context with
NBCON_PRIO_NORMAL under the device_lock.

3. The kthread is the only context which acquires the console
with NBCON_PRIO_NORMAL.

This is satisfied for all atomic printing call sites:

nbcon_legacy_emit_next_record() (#1)

nbcon_atomic_flush_pending_con() (#1)

nbcon_device_release() (#2)

It is even double guaranteed when @printk_kthreads_running
is set because then _only_ the kthread will print for
NBCON_PRIO_NORMAL. (#3)

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Use thread callback if in task context for legacy

When printing via console_lock, the write_atomic() callback is
used for nbcon consoles. However, if it is known that the
current cont

printk: nbcon: Use thread callback if in task context for legacy

When printing via console_lock, the write_atomic() callback is
used for nbcon consoles. However, if it is known that the
current context is a task context, the write_thread() callback
can be used instead.

Using write_thread() instead of write_atomic() helps to reduce
large disabled preemption regions when the device_lock does not
disable preemption.

This is mainly a preparatory change to allow avoiding
write_atomic() completely during normal operation if boot
consoles are registered.

As a side-effect, it also allows consolidating the printing
code for legacy printing and the kthread printer.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Relocate nbcon_atomic_emit_one()

Move nbcon_atomic_emit_one() so that it can be used by
nbcon_kthread_func() in a follow-up commit.

Signed-off-by: John Ogness <john.ogness@linutronix

printk: nbcon: Relocate nbcon_atomic_emit_one()

Move nbcon_atomic_emit_one() so that it can be used by
nbcon_kthread_func() in a follow-up commit.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Introduce printer kthreads

Provide the main implementation for running a printer kthread
per nbcon console that is takeover/handover aware. This
includes:

- new mandatory write_threa

printk: nbcon: Introduce printer kthreads

Provide the main implementation for running a printer kthread
per nbcon console that is takeover/handover aware. This
includes:

- new mandatory write_thread() callback
- kthread creation
- kthread main printing loop
- kthread wakeup mechanism
- kthread shutdown

kthread creation is a bit tricky because consoles may register
before kthreads can be created. In such cases, registration
will succeed, even though no kthread exists. Once kthreads can
be created, an early_initcall will set @printk_kthreads_ready.
If there are no registered boot consoles, the early_initcall
creates the kthreads for all registered nbcon consoles. If
kthread creation fails, the related console is unregistered.

If there are registered boot consoles when
@printk_kthreads_ready is set, no kthreads are created until
the final boot console unregisters.

Once kthread creation finally occurs, @printk_kthreads_running
is set so that the system knows kthreads are available for all
registered nbcon consoles.

If @printk_kthreads_running is already set when the console
is registering, the kthread is created during registration. If
kthread creation fails, the registration will fail.

Until @printk_kthreads_running is set, console printing occurs
directly via the console_lock.

kthread shutdown on system shutdown/reboot is necessary to
ensure the printer kthreads finish their printing so that the
system can cleanly transition back to direct printing via the
console_lock in order to reliably push out the final
shutdown/reboot messages. @printk_kthreads_running is cleared
before shutting down the individual kthreads.

The kthread uses a new mandatory write_thread() callback that
is called with both device_lock() and the console context
acquired.

The console ownership handling is necessary for synchronization
against write_atomic() which is synchronized only via the
console context ownership.

The device_lock() serializes acquiring the console context with
NBCON_PRIO_NORMAL. It is needed in case the device_lock() does
not disable preemption. It prevents the following race:

CPU0 CPU1

[ task A ]

nbcon_context_try_acquire()
# success with NORMAL prio
# .unsafe == false; // safe for takeover

[ schedule: task A -> B ]

WARN_ON()
nbcon_atomic_flush_pending()
nbcon_context_try_acquire()
# success with EMERGENCY prio

# flushing
nbcon_context_release()

# HERE: con->nbcon_state is free
# to take by anyone !!!

nbcon_context_try_acquire()
# success with NORMAL prio [ task B ]

[ schedule: task B -> A ]

nbcon_enter_unsafe()
nbcon_context_can_proceed()

BUG: nbcon_context_can_proceed() returns "true" because
the console is owned by a context on CPU0 with
NBCON_PRIO_NORMAL.

But it should return "false". The console is owned
by a context from task B and we do the check
in a context from task A.

Note that with these changes, the printer kthreads do not yet
take over full responsibility for nbcon printing during normal
operation. These changes only focus on the lifecycle of the
kthreads.

Co-developed-by: John Ogness <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Signed-off-by: Thomas Gleixner (Intel) <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Init @nbcon_seq to highest possible

When initializing an nbcon console, have nbcon_alloc() set
@nbcon_seq to the highest possible sequence number. For all
practical purposes, this wil

printk: nbcon: Init @nbcon_seq to highest possible

When initializing an nbcon console, have nbcon_alloc() set
@nbcon_seq to the highest possible sequence number. For all
practical purposes, this will guarantee that the console
will have nothing to print until later when @nbcon_seq is
set to the proper initial printing value.

This will be particularly important once kthread printing is
introduced because nbcon_alloc() can create/start the kthread
before the desired initial sequence number is known.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Add context to usable() and emit()

The nbcon consoles will have two callbacks to be used for
different contexts. In order to determine if an nbcon console
is usable, console_is_usable

printk: nbcon: Add context to usable() and emit()

The nbcon consoles will have two callbacks to be used for
different contexts. In order to determine if an nbcon console
is usable, console_is_usable() must know if it is a context
that will need to use the optional write_atomic() callback.
Also, nbcon_emit_next_record() must know which callback it
needs to call.

Add an extra parameter @use_atomic to console_is_usable() and
nbcon_emit_next_record() to specify this.

Since so far only the write_atomic() callback exists,
@use_atomic is set to true for all call sites.

For legacy consoles, @use_atomic is not used.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Add function for printers to reacquire ownership

Since ownership can be lost at any time due to handover or
takeover, a printing context _must_ be prepared to back out
immediately and

printk: nbcon: Add function for printers to reacquire ownership

Since ownership can be lost at any time due to handover or
takeover, a printing context _must_ be prepared to back out
immediately and carefully. However, there are scenarios where
the printing context must reacquire ownership in order to
finalize or revert hardware changes.

One such example is when interrupts are disabled during
printing. No other context will automagically re-enable the
interrupts. For this case, the disabling context _must_
reacquire nbcon ownership so that it can re-enable the
interrupts.

Provide nbcon_reacquire_nobuf() for exactly this purpose. It
allows a printing context to reacquire ownership using the same
priority as its previous ownership.

Note that after a successful reacquire the printing context
will have no output buffer because that has been lost. This
function cannot be used to resume printing.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Use raw_cpu_ptr() instead of open coding

There is no need to open code a non-migration-checking
this_cpu_ptr(). That is exactly what raw_cpu_ptr() is.

Signed-off-by: John Ogness <joh

printk: nbcon: Use raw_cpu_ptr() instead of open coding

There is no need to open code a non-migration-checking
this_cpu_ptr(). That is exactly what raw_cpu_ptr() is.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Implement emergency sections

In emergency situations (something has gone wrong but the
system continues to operate), usually important information
(such as a backtrace) is generated v

printk: nbcon: Implement emergency sections

In emergency situations (something has gone wrong but the
system continues to operate), usually important information
(such as a backtrace) is generated via printk(). This
information should be pushed out to the consoles ASAP.

Add per-CPU emergency nesting tracking because an emergency
can arise while in an emergency situation.

Add functions to mark the beginning and end of emergency
sections where the urgent messages are generated.

Perform direct console flushing at the emergency priority if
the current CPU is in an emergency state and it is safe to do
so.

Note that the emergency state is not system-wide. While one CPU
is in an emergency state, another CPU may attempt to print
console messages at normal priority.

Also note that printk() already attempts to flush consoles in
the caller context for normal priority. However, follow-up
changes will introduce printing kthreads, in which case the
normal priority printk() calls will offload to the kthreads.

Co-developed-by: John Ogness <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Signed-off-by: Thomas Gleixner (Intel) <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: Add helper for flush type logic

There are many call sites where console flushing occur.
Depending on the system state and types of consoles, the flush
methods to use are different. A flush c

printk: Add helper for flush type logic

There are many call sites where console flushing occur.
Depending on the system state and types of consoles, the flush
methods to use are different. A flush call site generally must
consider:

@have_boot_console
@have_nbcon_console
@have_legacy_console
@legacy_allow_panic_sync
is_printk_preferred()

and take into account the current CPU state:

NBCON_PRIO_NORMAL
NBCON_PRIO_EMERGENCY
NBCON_PRIO_PANIC

in order to decide if it should:

flush nbcon directly via atomic_write() callback
flush legacy directly via console_unlock
flush legacy via offload to irq_work

All of these call sites use their own logic to make this
decision, which is complicated and error prone. Especially
later when two more flush methods will be introduced:

flush nbcon via offload to kthread
flush legacy via offload to kthread

Introduce a new internal struct console_flush_type that specifies
which console flushing methods should be used in the context of
the caller.

Introduce a helper function to fill out console_flush_type to
be used for flushing call sites.

Replace the logic of all flushing call sites to use the new
helper.

This change standardizes behavior, leading to both fixes and
optimizations across various call sites. For instance, in
console_cpu_notify(), the new logic ensures that nbcon consoles
are flushed when they aren’t managed by the legacy loop.
Similarly, in console_flush_on_panic(), the system no longer
needs to flush nbcon consoles if none are present.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[[email protected]: Updated the commit message.]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Add unsafe flushing on panic

Add nbcon_atomic_flush_unsafe() to flush all nbcon consoles
using the write_atomic() callback and allowing unsafe hostile
takeovers. Call this at the end

printk: nbcon: Add unsafe flushing on panic

Add nbcon_atomic_flush_unsafe() to flush all nbcon consoles
using the write_atomic() callback and allowing unsafe hostile
takeovers. Call this at the end of panic() as a final attempt
to flush any pending messages.

Note that legacy consoles use unsafe methods for flushing
from the beginning of panic (see bust_spinlocks()). Therefore,
systems using both legacy and nbcon consoles may still fail to
see panic messages due to unsafe legacy console usage.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Flush new records on device_release()

There may be new records that were added while a driver was
holding the nbcon context for non-printing purposes. These
new records must be flushe

printk: nbcon: Flush new records on device_release()

There may be new records that were added while a driver was
holding the nbcon context for non-printing purposes. These
new records must be flushed by the nbcon_device_release()
context because no other context will do it.

If boot consoles are registered, the legacy loop is used
(either direct or per irq_work) to handle the flushing.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Use nbcon consoles in console_flush_all()

Allow nbcon consoles to print messages in the legacy printk()
caller context (printing via unlock) by integrating them into
console_flush_all

printk: nbcon: Use nbcon consoles in console_flush_all()

Allow nbcon consoles to print messages in the legacy printk()
caller context (printing via unlock) by integrating them into
console_flush_all(). The write_atomic() callback is used for
printing.

Provide nbcon_legacy_emit_next_record(), which acts as the
nbcon variant of console_emit_next_record(). Call this variant
within console_flush_all() for nbcon consoles. Since nbcon
consoles use their own @nbcon_seq variable to track the next
record to print, this also must be appropriately handled in
console_flush_all().

Note that the legacy printing logic uses @handover to detect
handovers for printing all consoles. For nbcon consoles,
handovers/takeovers occur on a per-console basis and thus do
not cause the console_flush_all() loop to abort.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Provide function to flush using write_atomic()

Provide nbcon_atomic_flush_pending() to perform flushing of all
registered nbcon consoles using their write_atomic() callback.

Unlike c

printk: nbcon: Provide function to flush using write_atomic()

Provide nbcon_atomic_flush_pending() to perform flushing of all
registered nbcon consoles using their write_atomic() callback.

Unlike console_flush_all(), nbcon_atomic_flush_pending() will
only flush up through the newest record at the time of the
call. This prevents a CPU from printing unbounded when other
CPUs are adding records. If new records are added while
flushing, it is expected that the dedicated printer threads
will print those records. If the printer thread is not
available (which is always the case at this point in the
rework), nbcon_atomic_flush_pending() _will_ flush all records
in the ringbuffer.

Unlike console_flush_all(), nbcon_atomic_flush_pending() will
fully flush one console before flushing the next. This helps to
guarantee that a block of pending records (such as a stack
trace in an emergency situation) can be printed atomically at
once before releasing console ownership.

nbcon_atomic_flush_pending() is safe in any context because it
uses write_atomic() and acquires with unsafe_takeover disabled.

Co-developed-by: John Ogness <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Signed-off-by: Thomas Gleixner (Intel) <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Add helper to assign priority based on CPU state

Add a helper function to use the current state of the CPU to
determine which priority to assign to the printing context.

The EMERGENC

printk: nbcon: Add helper to assign priority based on CPU state

Add a helper function to use the current state of the CPU to
determine which priority to assign to the printing context.

The EMERGENCY priority handling is added in a follow-up commit.
It will use a per-CPU variable.

Note: nbcon_device_try_acquire(), which is used by console
drivers to acquire the nbcon console for non-printing
activities, is hard-coded to always use NORMAL priority.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

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printk: nbcon: Do not rely on proxy headers

The headers kernel.h, serial_core.h, and console.h allow for the
definitions of many types and functions from other headers.
Rather than relying on these

printk: nbcon: Do not rely on proxy headers

The headers kernel.h, serial_core.h, and console.h allow for the
definitions of many types and functions from other headers.
Rather than relying on these as proxy headers, explicitly
include all headers providing needed definitions. Also sort the
list alphabetically to be able to easily detect duplicates.

Suggested-by: Andy Shevchenko <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Acked-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

nbcon: Add API to acquire context for non-printing operations

Provide functions nbcon_device_try_acquire() and
nbcon_device_release() which will try to acquire the nbcon
console ownership with NBCON

nbcon: Add API to acquire context for non-printing operations

Provide functions nbcon_device_try_acquire() and
nbcon_device_release() which will try to acquire the nbcon
console ownership with NBCON_PRIO_NORMAL and mark it unsafe for
handover/takeover.

These functions are to be used together with the device-specific
locking when performing non-printing activities on the console
device. They will allow synchronization against the
atomic_write() callback which will be serialized, for higher
priority contexts, only by acquiring the console context
ownership.

Pitfalls:

The API requires to be called in a context with migration
disabled because it uses per-CPU variables internally.

The context is set unsafe for a takeover all the time. It
guarantees full serialization against any atomic_write() caller
except for the final flush in panic() which might try an unsafe
takeover.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Remove return value for write_atomic()

The return value of write_atomic() does not provide any useful
information. On the contrary, it makes things more complicated
for the caller to

printk: nbcon: Remove return value for write_atomic()

The return value of write_atomic() does not provide any useful
information. On the contrary, it makes things more complicated
for the caller to appropriately deal with the information.

Change write_atomic() to not have a return value. If the
message did not get printed due to loss of ownership, the
caller will notice this on its own. If ownership was not lost,
it will be assumed that the driver successfully printed the
message and the sequence number for that console will be
incremented.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Clarify rules of the owner/waiter matching

The functions nbcon_owner_matches() and nbcon_waiter_matches()
use a minimal set of data to determine if a context matches.
The existing ker

printk: nbcon: Clarify rules of the owner/waiter matching

The functions nbcon_owner_matches() and nbcon_waiter_matches()
use a minimal set of data to determine if a context matches.
The existing kerneldoc and comments were not clear enough and
caused the printk folks to re-prove that the functions are
indeed reliable in all cases.

Update and expand the explanations so that it is clear that the
implementations are sufficient for all cases.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

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printk: Properly deal with nbcon consoles on seq init

If a non-boot console is registering and boot consoles exist,
the consoles are flushed before being unregistered. This allows
the non-boot conso

printk: Properly deal with nbcon consoles on seq init

If a non-boot console is registering and boot consoles exist,
the consoles are flushed before being unregistered. This allows
the non-boot console to continue where the boot console left
off.

If for whatever reason flushing fails, the lowest seq found from
any of the enabled boot consoles is used. Until now con->seq was
checked. However, if it is an nbcon boot console, the function
nbcon_seq_read() must be used to read seq because con->seq is
not updated for nbcon consoles.

Check if it is an nbcon boot console and if so call
nbcon_seq_read() to read seq.

Also, avoid usage of con->seq as temporary storage of the
starting record. Instead, rename console_init_seq() to
get_init_console_seq() and just return the value. For nbcon
consoles set the sequence via nbcon_seq_force(), for legacy
consoles set con->seq.

The cleaned design should make sure that the value stays and is
set before the console is added to the console list. It also
unifies the sequence number initialization for legacy and nbcon
consoles.

Reviewed-by: John Ogness <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

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printk: nbcon: Consolidate alloc() and init()

Rather than splitting the nbcon allocation and initialization into
two pieces, perform all initialization in nbcon_alloc(). Later,
the initial sequence

printk: nbcon: Consolidate alloc() and init()

Rather than splitting the nbcon allocation and initialization into
two pieces, perform all initialization in nbcon_alloc(). Later,
the initial sequence is calculated and can be explicitly set using
nbcon_seq_force(). This removes the need for the strong rules of
nbcon_init() that even included a BUG_ON().

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

show more ...

printk: nbcon: Relocate 32bit seq macros

The macros __seq_to_nbcon_seq() and __nbcon_seq_to_seq() are
used to provide support for atomic handling of sequence numbers
on 32bit systems. Until now this

printk: nbcon: Relocate 32bit seq macros

The macros __seq_to_nbcon_seq() and __nbcon_seq_to_seq() are
used to provide support for atomic handling of sequence numbers
on 32bit systems. Until now this was only used by nbcon.c,
which is why they were located in nbcon.c and include nbcon in
the name.

In a follow-up commit this functionality is also needed by
printk_ringbuffer. Rather than duplicating the functionality,
relocate the macros to printk_ringbuffer.h.

Also, since the macros will be no longer nbcon-specific, rename
them to __u64seq_to_ulseq() and __ulseq_to_u64seq().

This does not result in any functional change.

Signed-off-by: John Ogness <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Mladek <[email protected]>

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printk: nbcon: Allow drivers to mark unsafe regions and check state

For the write_atomic callback, the console driver may have unsafe
regions that need to be appropriately marked. Provide functions

printk: nbcon: Allow drivers to mark unsafe regions and check state

For the write_atomic callback, the console driver may have unsafe
regions that need to be appropriately marked. Provide functions
that accept the nbcon_write_context struct to allow for the driver
to enter and exit unsafe regions.

Also provide a function for drivers to check if they are still the
owner of the console.

Co-developed-by: John Ogness <[email protected]>
Signed-off-by: John Ogness <[email protected]>
Signed-off-by: Thomas Gleixner (Intel) <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Signed-off-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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