The macro for_each_console_srcu iterates over all registered consoles. It's
implied that all registered consoles have CON_ENABLED flag set, making
the check for the flag unnecessary. Call console_is_usable function to
fully verify if the given console is usable before calling the ->unblank
callback.
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251121-printk-cleanup-part2-v2-3-57b8b78647f4@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
All consoles found on for_each_console are registered, meaning that all
of them have the CON_ENABLED flag set. Since NBCON was introduced it's
important to check if a given console also implements the NBCON callbacks.
The function console_is_usable does exactly that.
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251121-printk-cleanup-part2-v2-2-57b8b78647f4@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
The original code tried to find a console that has CON_BOOT _or_
CON_ENABLED flag set. The flag CON_ENABLED is set to all registered
consoles, so in this case this check is always true, even for the
CON_BOOT consoles.
The initial intent of the kgdboc_earlycon_init was to get a console
early (CON_BOOT) or later on in the process (CON_ENABLED). The
code was using for_each_console macro, meaning that all console structs
were previously registered on the printk() machinery. At this point,
any console found on for_each_console is safe for kgdboc_earlycon_init
to use.
Dropping the check makes the code cleaner, and avoids further confusion
by future readers of the code.
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251121-printk-cleanup-part2-v2-1-57b8b78647f4@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
We have two almost identical pieces that handle FORMAT_STATE_NUM case.
The differences are:
- redundant {} for one-line if-else conditional
- missing blank line after variable definitions
- inverted conditional
Unify the style of two.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251120083140.3478507-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
With commit ("printk: Avoid scheduling irq_work on suspend") the
implementation of printk_get_console_flush_type() was modified to
avoid offloading when irq_work should be blocked during suspend.
Since printk uses the returned flush type to determine what
flushing methods are used, this was thought to be sufficient for
avoiding irq_work usage during the suspend phase.
However, vprintk_emit() implements a hack to support
printk_deferred(). In this hack, the returned flush type is
adjusted to make sure no legacy direct printing occurs when
printk_deferred() was used.
Because of this hack, the legacy offloading flushing method can
still be used, causing irq_work to be queued when it should not
be.
Adjust the vprintk_emit() hack to also consider
@console_irqwork_blocked so that legacy offloading will not be
chosen when irq_work should be blocked.
Link: https://lore.kernel.org/lkml/87fra90xv4.fsf@jogness.linutronix.de
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Fixes: 26873e3e7f ("printk: Avoid scheduling irq_work on suspend")
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
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: 6b93bb41f6 ("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 <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://patch.msgid.link/20251113160351.113031-3-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
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 6690d6b527 ("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 <pmladek@suse.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/stable/20251113160351.113031-2-john.ogness%40linutronix.de
Tested-by: Sherry Sun <sherry.sun@nxp.com>
Link: https://patch.msgid.link/20251113160351.113031-2-john.ogness@linutronix.de
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-22-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Karan Tilak Kumar <kartilak@cisco.com>
Link: https://patch.msgid.link/20251113150217.3030010-21-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Karan Tilak Kumar <kartilak@cisco.com>
Link: https://patch.msgid.link/20251113150217.3030010-20-andriy.shevchenko@linux.intel.com
[pmladek@suse.com: Fixed output ordering and last_read_time update.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20251113150217.3030010-19-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
While at it, fix wrong use of %ptT against struct timespec64.
It's kinda lucky that it worked just because the first member
there 64-bit and it's of time64_t type. Now with %ptS it may
be used correctly.
Acked-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-18-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Rodolfo Giometti <giometti@enneenne.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-17-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-16-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Vladimir Oltean <olteanv@gmail.com>
Tested-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://patch.msgid.link/20251113150217.3030010-15-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://patch.msgid.link/20251113150217.3030010-14-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Hans Verkuil <hverkuil+cisco@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-13-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-12-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-11-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-10-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-9-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-8-andriy.shevchenko@linux.intel.com
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://patch.msgid.link/20251113150217.3030010-7-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-6-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-5-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-4-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Use %ptSp instead of open coded variants to print content of
struct timespec64 in human readable format.
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251113150217.3030010-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
A handful drivers want to print a content of the struct timespec64
in a format of %lld:%09ld. In order to make their lives easier, add
the respecting specifier directly to the printf() implementation.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251113150217.3030010-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Two functions use the same specifier data for the special hex number.
Almost the same as the field width is calculated on the size of the
given type. Due to that, make a compound literal macro in order to
deduplicate the rest.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251113150313.3030700-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
The pointer may be invalid when gets to the printf(). In particular
the time_and_date() dereferencing it in some cases without checking.
Move the check from rtc_str() to time_and_date() to cover all cases.
Fixes: 7daac5b2fd ("lib/vsprintf: Print time64_t in human readable format")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251110132118.4113976-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
The decision whether some more space is needed is tricky in the printk
ring buffer code:
1. The given lpos values might overflow. A subtraction must be used
instead of a simple "lower than" check.
2. Another CPU might reuse the space in the mean time. It can be
detected when the subtraction is bigger than DATA_SIZE(data_ring).
3. There is exactly enough space when the result of the subtraction
is zero. But more space is needed when the result is exactly
DATA_SIZE(data_ring).
Add a helper function to make sure that the check is done correctly
in all situations. Also it helps to make the code consistent and
better documented.
Suggested-by: John Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/87tsz7iea2.fsf@jogness.linutronix.de
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20251107194720.1231457-3-pmladek@suse.com
[pmladek@suse.com: Updated wording as suggested by John]
Signed-off-by: Petr Mladek <pmladek@suse.com>
The files in Documentation/core-api/ are by virtue of their top-level
directory part of the Documentation section in MAINTAINERS. Each file in
Documentation/core-api/ should however also have a further section in
MAINTAINERS it belongs to, which fits to the technical area of the
documented API in that file.
The printk.rst provides some explanation to the printk API defined in
include/linux/printk.h, which itself is part of the PRINTK section.
Add this core-api document to PRINTK.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@redhat.com>
Link: https://patch.msgid.link/20251105102832.155823-1-lukas.bulwahn@redhat.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
Clarify that the return values of vsprintf() and sprintf() exclude the
trailing NUL character.
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251103090913.2066-2-thorsten.blum@linux.dev
Signed-off-by: Petr Mladek <pmladek@suse.com>
printk() tries to flush messages with NBCON_PRIO_EMERGENCY on
nbcon consoles immediately. It might take seconds to flush all
pending lines on slow serial consoles. Note that there might be
hundreds of messages, for example:
[ 3.771531][ T1] pci 0000:3e:08.1: [8086:324
** replaying previous printk message **
[ 3.771531][ T1] pci 0000:3e:08.1: [8086:3246] type 00 class 0x088000 PCIe Root Complex Integrated Endpoint
[ ... more than 2000 lines, about 200kB messages ... ]
[ 3.837752][ T1] pci 0000:20:01.0: Adding to iommu group 18
[ 3.837851][ T
** replaying previous printk message **
[ 3.837851][ T1] pci 0000:20:03.0: Adding to iommu group 19
[ 3.837946][ T1] pci 0000:20:05.0: Adding to iommu group 20
[ ... more than 500 messages for iommu groups 21-590 ...]
[ 3.912932][ T1] pci 0000:f6:00.1: Adding to iommu group 591
[ 3.913070][ T1] pci 0000:f6:00.2: Adding to iommu group 592
[ 3.913243][ T1] DMAR: Intel(R) Virtualization Technology for Directed I/O
[ 3.913245][ T1] PCI-DMA: Using software bounce buffering for IO (SWIOTLB)
[ 3.913245][ T1] software IO TLB: mapped [mem 0x000000004f000000-0x0000000053000000] (64MB)
[ 3.913324][ T1] RAPL PMU: API unit is 2^-32 Joules, 3 fixed counters, 655360 ms ovfl timer
[ 3.913325][ T1] RAPL PMU: hw unit of domain package 2^-14 Joules
[ 3.913326][ T1] RAPL PMU: hw unit of domain dram 2^-14 Joules
[ 3.913327][ T1] RAPL PMU: hw unit of domain psys 2^-0 Joules
[ 3.933486][ T1] ------------[ cut here ]------------
[ 3.933488][ T1] WARNING: CPU: 2 PID: 1 at arch/x86/events/intel/uncore.c:1156 uncore_pci_pmu_register+0x15e/0x180
[ 3.930291][ C0] watchdog: Watchdog detected hard LOCKUP on cpu 0
[ 3.930291][ C0] Kernel panic - not syncing: Hard LOCKUP
[...]
[ 3.930291][ C0] CPU: 0 UID: 0 PID: 18 Comm: pr/ttyS0 Not tainted...
[...]
[ 3.930291][ C0] RIP: 0010:nbcon_reacquire_nobuf+0x11/0x50
[ 3.930291][ C0] Call Trace:
[...]
[ 3.930291][ C0] <TASK>
[ 3.930291][ C0] serial8250_console_write+0x16d/0x5c0
[ 3.930291][ C0] nbcon_emit_next_record+0x22c/0x250
[ 3.930291][ C0] nbcon_emit_one+0x93/0xe0
[ 3.930291][ C0] nbcon_kthread_func+0x13c/0x1c0
The are visible two takeovers of the console ownership:
- The 1st one is triggered by the "WARNING: CPU: 2 PID: 1 at
arch/x86/..." line printed with NBCON_PRIO_EMERGENCY.
- The 2nd one is triggered by the "Kernel panic - not syncing:
Hard LOCKUP" line printed with NBCON_PRIO_PANIC.
There are more than 2500 lines, at about 240kB, emitted between
the takeover and the 1st "WARNING" line in the emergency context.
This amount of pending messages had to be flushed by
nbcon_atomic_flush_pending() when WARN() printed its first line.
The atomic flush was holding the nbcon console context for too long so
that it triggered hard lockup on the CPU running the printk kthread
"pr/ttyS0". The kthread needed to reacquire the console ownership
for restoring the original serial port state in serial8250_console_write().
Prevent the hardlockup by releasing the nbcon console ownership after
each emitted record.
Note that __nbcon_atomic_flush_pending_con() used to hold the console
ownership all the time because it blocked the printk kthread. Otherwise
the kthread tried to flush the messages in parallel which caused repeated
takeovers and more replayed messages.
It is not longer a problem because the repeated takeovers are blocked
by the counter of emergency contexts, see nbcon_cpu_emergency_cnt.
Link: https://lore.kernel.org/all/aNQO-zl3k1l4ENfy@pathway.suse.cz
Reviewed-by: Andrew Murray <amurray@thegoodpenguin.co.uk>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20250926124912.243464-4-pmladek@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
The printk kthread might be running when there is a panic in progress.
But it is not able to acquire the console ownership any longer.
Prevent the desperate attempts to acquire the ownership and allow sleeping
in panic. It would make it behave the same as when there is any CPU
in an emergency context.
Reviewed-by: Andrew Murray <amurray@thegoodpenguin.co.uk>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20250926124912.243464-3-pmladek@suse.com
[pmladek@suse.com: Rebased on top of 6.18-rc1 (panic_in_progress() moved to panic.c)]
Signed-off-by: Petr Mladek <pmladek@suse.com>
In emergency contexts, printk() tries to flush messages directly even
on nbcon consoles. And it is allowed to takeover the console ownership
and interrupt the printk kthread in the middle of a message.
Only one takeover and one repeated message should be enough in most
situations. The first emergency message flushes the backlog and printk
kthreads get to sleep. Next emergency messages are flushed directly
and printk() does not wake up the kthreads.
However, the one takeover is not guaranteed. Any printk() in normal
context on another CPU could wake up the kthreads. Or a new emergency
message might be added before the kthreads get to sleep. Note that
the interrupted .write_thread() callbacks usually have to call
nbcon_reacquire_nobuf() and restore the original device setting
before checking for pending messages.
The risk of the repeated takeovers will be even bigger because
__nbcon_atomic_flush_pending_con is going to release the console
ownership after each emitted record. It will be needed to prevent
hardlockup reports on other CPUs which are busy waiting for
the context ownership, for example, by nbcon_reacquire_nobuf() or
__uart_port_nbcon_acquire().
The repeated takeovers break the output, for example:
[ 5042.650211][ T2220] Call Trace:
[ 5042.6511
** replaying previous printk message **
[ 5042.651192][ T2220] <TASK>
[ 5042.652160][ T2220] kunit_run_
** replaying previous printk message **
[ 5042.652160][ T2220] kunit_run_tests+0x72/0x90
[ 5042.653340][ T22
** replaying previous printk message **
[ 5042.653340][ T2220] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5042.654628][ T2220] ? stack_trace_save+0x4d/0x70
[ 5042.6553
** replaying previous printk message **
[ 5042.655394][ T2220] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5042.656713][ T2220] ? save_trace+0x5b/0x180
A more robust solution is to block the printk kthread entirely whenever
*any* CPU enters an emergency context. This ensures that critical messages
can be flushed without contention from the normal, non-atomic printing
path.
Link: https://lore.kernel.org/all/aNQO-zl3k1l4ENfy@pathway.suse.cz
Reviewed-by: Andrew Murray <amurray@thegoodpenguin.co.uk>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20250926124912.243464-2-pmladek@suse.com
[pmladek@suse.com: Added changes proposed by John Ogness]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Function kdb_msg_write was calling con->write for any found console,
but it won't work on NBCON consoles. In this case we should acquire the
ownership of the console using NBCON_PRIO_EMERGENCY, since printing
kdb messages should only be interrupted by a panic.
At this point, the console is required to use the atomic callback. The
console is skipped if the write_atomic callback is not set or if the
context could not be acquired. The validation of NBCON is done by the
console_is_usable helper. The context is released right after
write_atomic finishes.
The oops_in_progress handling is only needed in the legacy consoles,
so it was moved around the con->write callback.
Suggested-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Link: https://patch.msgid.link/20251016-nbcon-kgdboc-v6-5-866aac60a80e@suse.com
[pmladek@suse.com: Fixed compilation with !CONFIG_PRINTK.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
This function will be used in the next patch to allow a driver to set
both the message and message length of a nbcon_write_context. This is
necessary because the function also initializes the ->unsafe_takeover
struct member. By using this helper we ensure that the struct is
initialized correctly.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Link: https://patch.msgid.link/20251016-nbcon-kgdboc-v6-4-866aac60a80e@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
KDB can interrupt any console to execute the "mirrored printing" at any
time, so add an exception to nbcon_context_try_acquire_direct to allow
to get the context if the current CPU is the same as kdb_printf_cpu.
This change will be necessary for the next patch, which fixes
kdb_msg_write to work with NBCON consoles by calling ->write_atomic on
such consoles. But to print it first needs to acquire the ownership of
the console, so nbcon_context_try_acquire_direct is fixed here.
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Link: https://patch.msgid.link/20251016-nbcon-kgdboc-v6-3-866aac60a80e@suse.com
[pmladek@suse.com: Fix compilation with !CONFIG_KGDB_KDB.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
These helpers will be used when calling console->write_atomic on
KDB code in the next patch. It's basically the same implementation
as nbcon_device_try_acquire, but using NBCON_PRIO_EMERGENCY when
acquiring the context.
If the acquire succeeds, the message and message length are assigned to
nbcon_write_context so ->write_atomic can print the message.
After release try to flush the console since there may be a backlog of
messages in the ringbuffer. The kthread console printers do not get a
chance to run while kdb is active.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Link: https://patch.msgid.link/20251016-nbcon-kgdboc-v6-2-866aac60a80e@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
The helper will be used on KDB code in the next commits.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Link: https://patch.msgid.link/20251016-nbcon-kgdboc-v6-1-866aac60a80e@suse.com
Signed-off-by: Petr Mladek <pmladek@suse.com>
The legacy printer kthread uses console_lock and
__console_flush_and_unlock to flush records to the console. This
approach results in the console_lock being held for the entire
duration of a flush. This can result in large waiting times for
those waiting for console_lock especially where there is a large
volume of records or where the console is slow (e.g. serial). This
contention is observed during boot, as the call to filp_open in
console_on_rootfs will delay progression to userspace until any
in-flight flush is completed.
Let's instead use console_flush_one_record and release/reacquire
the console_lock between records.
On a PocketBeagle 2, with the following boot args:
"console=ttyS2,9600 initcall_debug=1 loglevel=10"
Without this patch:
[ 5.613166] +console_on_rootfs/filp_open
[ 5.643473] mmc1: SDHCI controller on fa00000.mmc [fa00000.mmc] using ADMA 64-bit
[ 5.643823] probe of fa00000.mmc returned 0 after 258244 usecs
[ 5.710520] mmc1: new UHS-I speed SDR104 SDHC card at address 5048
[ 5.721976] mmcblk1: mmc1:5048 SD32G 29.7 GiB
[ 5.747258] mmcblk1: p1 p2
[ 5.753324] probe of mmc1:5048 returned 0 after 40002 usecs
[ 15.595240] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30040000.pruss
[ 15.595282] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e010000.watchdog
[ 15.595297] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e000000.watchdog
[ 15.595437] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30300000.crc
[ 146.275961] -console_on_rootfs/filp_open ...
and with:
[ 5.477122] +console_on_rootfs/filp_open
[ 5.595814] mmc1: SDHCI controller on fa00000.mmc [fa00000.mmc] using ADMA 64-bit
[ 5.596181] probe of fa00000.mmc returned 0 after 312757 usecs
[ 5.662813] mmc1: new UHS-I speed SDR104 SDHC card at address 5048
[ 5.674367] mmcblk1: mmc1:5048 SD32G 29.7 GiB
[ 5.699320] mmcblk1: p1 p2
[ 5.705494] probe of mmc1:5048 returned 0 after 39987 usecs
[ 6.418682] -console_on_rootfs/filp_open ...
...
[ 15.593509] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30040000.pruss
[ 15.593551] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e010000.watchdog
[ 15.593566] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to e000000.watchdog
[ 15.593704] ti_sci_pm_domains 44043000.system-controller:power-controller: sync_state() pending due to 30300000.crc
Where I've added a printk surrounding the call in console_on_rootfs
to filp_open.
Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Murray <amurray@thegoodpenguin.co.uk>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20251020-printk_legacy_thread_console_lock-v3-3-00f1f0ac055a@thegoodpenguin.co.uk
[pmladek@suse.com: Fixed ordering of variable definition suggested by John.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
console_flush_one_record() and console_flush_all() duplicate several
checks. They both want to tell the caller that consoles are not
longer usable in this context because it has lost the lock or
the lock has to be reserved for the panic CPU.
Remove the duplication by changing the semantic of the function
console_flush_one_record() return value and parameters.
The function will return true when it is able to do the job. It means
that there is at least one usable console. And the flushing was
not interrupted by a takeover or panic_on_other_cpu().
Also replace the @any_usable parameter with @try_again. The @try_again
parameter will be set to true when the function could do the job
and at least one console made a progress.
Motivation:
The callers need to know when
+ they should continue flushing => @try_again
+ when the console is flushed => can_do_the_job(return) && !@try_again
+ when @next_seq is valid => same as flushed
+ when lost console_lock => @takeover
The proposed change makes it clear when the function can do
the job. It simplifies the answer for the other questions.
Also the return value from console_flush_one_record() can
be used as return value from console_flush_all().
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20251020-printk_legacy_thread_console_lock-v3-2-00f1f0ac055a@thegoodpenguin.co.uk
[pmladek@suse.com: Fixed type of any_usable variable reported by John]
Signed-off-by: Petr Mladek <pmladek@suse.com>
console_flush_all prints all remaining records to all usable consoles
whilst its caller holds console_lock. This can result in large waiting
times for those waiting for console_lock especially where there is a
large volume of records or where the console is slow (e.g. serial).
Let's extract the parts of this function which print a single record
into a new function named console_flush_one_record. This can later
be used for functions that will release and reacquire console_lock
between records.
This commit should not change existing functionality.
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Murray <amurray@thegoodpenguin.co.uk>
Reviewed-by: John Ogness <john.ogness@linutronix.de>
Link: https://patch.msgid.link/20251020-printk_legacy_thread_console_lock-v3-1-00f1f0ac055a@thegoodpenguin.co.uk
Signed-off-by: Petr Mladek <pmladek@suse.com>
