linux.git/kernel/printk/internal.h, branch v6.6.131

printk: Rename abandon_console_lock_in_panic() to other_cpu_in_panic()

2023-07-20T11:06:22+00:00

Currently abandon_console_lock_in_panic() is only used to determine if
the current CPU should immediately release the console lock because
another CPU is in panic. However, later this function will be used by
the CPU to immediately release other resources in this situation.

Rename the function to other_cpu_in_panic(), which is a better
description and does not assume it is related to the console lock.

Signed-off-by: John Ogness 
Reviewed-by: Sergey Senozhatsky 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20230717194607.145135-8-john.ogness@linutronix.de

printk: adjust string limit macros

2023-01-11T14:35:12+00:00

The various internal size limit macros have names and/or values that
do not fit well to their current usage.

Rename the macros so that their purpose is clear and, if needed,
provide a more appropriate value. In general, the new macros and
values will lead to less memory usage. The new macros are...

PRINTK_MESSAGE_MAX:

This is the maximum size for a formatted message on a console,
devkmsg, or syslog. It does not matter which format the message has
(normal or extended). It replaces the use of CONSOLE_EXT_LOG_MAX for
console and devkmsg. It replaces the use of CONSOLE_LOG_MAX for
syslog.

Historically, normal messages have been allowed to print up to 1kB,
whereas extended messages have been allowed to print up to 8kB.
However, the difference in lengths of these message types is not
significant and in multi-line records, normal messages are probably
larger. Also, because 1kB is only slightly above the allowed record
size, multi-line normal messages could be easily truncated during
formatting.

This new macro should be significantly larger than the allowed
record size to allow sufficient space for extended or multi-line
prefix text. A value of 2kB should be plenty of space. For normal
messages this represents a doubling of the historically allowed
amount. For extended messages it reduces the excessive 8kB size,
thus reducing memory usage needed for message formatting.

PRINTK_PREFIX_MAX:

This is the maximum size allowed for a record prefix (used by
console and syslog). It replaces PREFIX_MAX. The value is left
unchanged.

PRINTKRB_RECORD_MAX:

This is the maximum size allowed to be reserved for a record in the
ringbuffer. It is used by all readers and writers with the printk
ringbuffer. It replaces LOG_LINE_MAX.

Previously this was set to "1kB - PREFIX_MAX", which makes some
sense if 1kB is the limit for normal message output and prefixes are
enabled. However, with the allowance of larger output and the
existence of multi-line records, the value is rather bizarre.

Round the value up to 1kB.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20230109100800.1085541-9-john.ogness@linutronix.de

printk: introduce console_prepend_dropped() for dropped messages

2023-01-11T14:35:11+00:00

Currently "dropped messages" are separately printed immediately
before printing the printk message. Since normal consoles are
now using an output buffer that is much larger than previously,
the "dropped message" could be prepended to the printk message
and then output everything in a single write() call.

Introduce a helper function console_prepend_dropped() to prepend
an existing message with a "dropped message". This simplifies
the code by allowing all message formatting to be handled
together and then only requires a single write() call to output
the full message. And since this helper does not require any
locking, it can be used in the future for other console printing
contexts as well.

Note that console_prepend_dropped() is defined as a NOP for
!CONFIG_PRINTK. Although the function will never be called for
!CONFIG_PRINTK, compiling the function can lead to warnings of
"always true" conditionals due to the size macro values used
in !CONFIG_PRINTK.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20230109100800.1085541-7-john.ogness@linutronix.de

printk: introduce printk_get_next_message() and printk_message

2023-01-11T14:35:11+00:00

Code for performing the console output is intermixed with code that
is formatting the output for that console. Introduce a new helper
function printk_get_next_message() to handle the reading and
formatting of the printk text. The helper does not require any
locking so that in the future it can be used for other printing
contexts as well.

This also introduces a new struct printk_message to wrap the struct
printk_buffers, adding metadata about its contents. This allows
users of printk_get_next_message() to receive all relevant
information about the message that was read and formatted.

Why is struct printk_message a wrapper struct?

It is intentional that a wrapper struct is introduced instead of
adding the metadata directly to struct printk_buffers. The upcoming
atomic consoles support multiple printing contexts per CPU. This
means that while a CPU is formatting a message, it can be
interrupted and the interrupting context may also format a (possibly
different) message. Since the printk buffers are rather large,
there will only be one struct printk_buffers per CPU and it must be
shared by the possible contexts of that CPU.

If the metadata was part of struct printk_buffers, interrupting
contexts would clobber the metadata being prepared by the
interrupted context. This could be handled by robustifying the
message formatting functions to cope with metadata unexpectedly
changing. However, this would require significant amounts of extra
data copying, also adding significant complexity to the code.

Instead, the metadata can live on the stack of the formatting
context and the message formatting functions do not need to be
concerned about the metadata changing underneath them.

Note that the message formatting functions can handle unexpected
text buffer changes. So it is perfectly OK if a shared text buffer
is clobbered by an interrupting context. The atomic console
implementation will recognize the interruption and avoid printing
the (probably garbage) text buffer.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20230109100800.1085541-6-john.ogness@linutronix.de

printk: introduce struct printk_buffers

2023-01-11T14:35:11+00:00

Introduce a new struct printk_buffers to contain all the buffers
needed to read and format a printk message for output. Putting the
buffers inside a struct reduces the number of buffer pointers that
need to be tracked. Also, it allows usage of the sizeof() macro for
the buffer sizes, rather than expecting certain sized buffers being
passed in.

Note that since the output buffer for normal consoles is now
CONSOLE_EXT_LOG_MAX instead of CONSOLE_LOG_MAX, multi-line
messages that may have been previously truncated will now be
printed in full. This should be considered a feature and not a bug
since the CONSOLE_LOG_MAX restriction was about limiting static
buffer usage rather than limiting printed text.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20230109100800.1085541-5-john.ogness@linutronix.de

printk: move size limit macros into internal.h

2023-01-11T14:35:11+00:00

The size limit macros are located further down in printk.c and
behind ifdef conditionals. This complicates their usage for
upcoming changes. Move the macros into internal.h so that they
are still invisible outside of printk, but easily accessible
for printk.

Also, the maximum size of formatted extended messages does not
need to be known by any code outside of printk, so move it to
internal.h as well. And like CONSOLE_LOG_MAX, for !CONFIG_PRINTK
set CONSOLE_EXT_LOG_MAX to 0 to reduce the static memory
footprint.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20230109100800.1085541-2-john.ogness@linutronix.de

Revert "printk: Wait for the global console lock when the system is going down"

2022-06-23T16:41:40+00:00

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 
Link: https://lore.kernel.org/r/20220623145157.21938-2-pmladek@suse.com

printk: Wait for the global console lock when the system is going down

2022-06-15T20:04:15+00:00

There are reports that the console kthreads block the global console
lock when the system is going down, for example, reboot, panic.

First part of the solution was to block kthreads in these problematic
system states so they stopped handling newly added messages.

Second part of the solution is to wait when for the kthreads when
they are actively printing. It solves the problem when a message
was printed before the system entered the problematic state and
the kthreads managed to step in.

A busy waiting has to be used because panic() can be called in any
context and in an unknown state of the scheduler.

There must be a timeout because the kthread might get stuck or sleeping
and never release the lock. The timeout 10s is an arbitrary value
inspired by the softlockup timeout.

Link: https://lore.kernel.org/r/20220610205038.GA3050413@paulmck-ThinkPad-P17-Gen-1
Link: https://lore.kernel.org/r/CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com
Signed-off-by: Petr Mladek 
Tested-by: Paul E. McKenney 
Link: https://lore.kernel.org/r/20220615162805.27962-3-pmladek@suse.com

printk: fix build warning when CONFIG_PRINTK=n

2022-01-22T06:33:36+00:00

build warning when CONFIG_PRINTK=n

	kernel/printk/printk.c:175:5: warning: no previous prototype for
	 'devkmsg_sysctl_set_loglvl' [-Wmissing-prototypes]

devkmsg_sysctl_set_loglvl() is only used in sysctl.c when
CONFIG_PRINTK=y, but it participates in the build when CONFIG_PRINTK=n.
So add compile dependency CONFIG_PRINTK=y && CONFIG_SYSCTL=y to fix the
build warning.

Link: https://lkml.kernel.org/r/20211129211943.640266-5-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni 
Signed-off-by: Luis Chamberlain 
Cc: Al Viro 
Cc: Anil S Keshavamurthy 
Cc: Antti Palosaari 
Cc: Christian Brauner 
Cc: "David S. Miller" 
Cc: Eric Biederman 
Cc: Eric Biggers 
Cc: Iurii Zaikin 
Cc: Kees Cook 
Cc: Lukas Middendorf 
Cc: Masami Hiramatsu 
Cc: "Naveen N. Rao" 
Cc: Stephen Kitt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: move printk sysctl to printk/sysctl.c

2022-01-22T06:33:35+00:00

kernel/sysctl.c is a kitchen sink where everyone leaves their dirty
dishes, this makes it very difficult to maintain.

To help with this maintenance let's start by moving sysctls to places
where they actually belong.  The proc sysctl maintainers do not want to
know what sysctl knobs you wish to add for your own piece of code, we
just care about the core logic.

So move printk sysctl from kernel/sysctl.c to kernel/printk/sysctl.c.
Use register_sysctl() to register the sysctl interface.

[mcgrof@kernel.org: fixed compile issues when PRINTK is not set, commit log update]

Link: https://lkml.kernel.org/r/20211124231435.1445213-6-mcgrof@kernel.org
Signed-off-by: Xiaoming Ni 
Signed-off-by: Luis Chamberlain 
Cc: Al Viro 
Cc: Amir Goldstein 
Cc: Andy Shevchenko 
Cc: Antti Palosaari 
Cc: Arnd Bergmann 
Cc: Benjamin Herrenschmidt 
Cc: Benjamin LaHaise 
Cc: Clemens Ladisch 
Cc: David Airlie 
Cc: Douglas Gilbert 
Cc: Eric Biederman 
Cc: Greg Kroah-Hartman 
Cc: Iurii Zaikin 
Cc: James E.J. Bottomley 
Cc: Jani Nikula 
Cc: Jani Nikula 
Cc: Jan Kara 
Cc: Joel Becker 
Cc: John Ogness 
Cc: Joonas Lahtinen 
Cc: Joseph Qi 
Cc: Julia Lawall 
Cc: Kees Cook 
Cc: Lukas Middendorf 
Cc: Mark Fasheh 
Cc: Martin K. Petersen 
Cc: Paul Turner 
Cc: Peter Zijlstra 
Cc: Petr Mladek 
Cc: Phillip Potter 
Cc: Qing Wang 
Cc: "Rafael J. Wysocki" 
Cc: Rodrigo Vivi 
Cc: Sebastian Reichel 
Cc: Sergey Senozhatsky 
Cc: Stephen Kitt 
Cc: Steven Rostedt (VMware) 
Cc: Suren Baghdasaryan 
Cc: Tetsuo Handa 
Cc: "Theodore Ts'o" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds