linux.git/kernel/printk, branch v6.12.80

printk: nbcon: Allow reacquire during panic

2025-08-20T16:30:47+00:00

[ Upstream commit 571c1ea91a73db56bd94054fabecd0f070dc90db ]

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 
Signed-off-by: Sasha Levin

printk: Check CON_SUSPEND when unblanking a console

2025-05-29T09:02:22+00:00

[ Upstream commit 72c96a2dacc0fb056d13a5f02b0845c4c910fe54 ]

The commit 9e70a5e109a4 ("printk: Add per-console suspended state")
introduced the CON_SUSPENDED flag for consoles. The suspended consoles
will stop receiving messages, so don't unblank suspended consoles
because it won't be showing anything either way.

Signed-off-by: Marcos Paulo de Souza 
Reviewed-by: Petr Mladek 
Reviewed-by: John Ogness 
Link: https://lore.kernel.org/r/20250226-printk-renaming-v1-5-0b878577f2e6@suse.com
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

Flush console log from kernel_power_off()

2025-04-20T08:15:12+00:00

[ Upstream commit 6ea9a1781c70a8be1fcdc49134fc1bf4baba8bca ]

Kernels built with CONFIG_PREEMPT_RT=y can lose significant console output
and shutdown time, which hides shutdown-time RCU issues from rcutorture.
Therefore, make pr_flush() public and invoke it after then last print
in kernel_power_off().

[ paulmck: Apply John Ogness feedback. ]
[ paulmck: Appy Sebastian Andrzej Siewior feedback. ]
[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney 
Reviewed-by: John Ogness 
Reviewed-by: Petr Mladek 
Cc: Steven Rostedt 
Cc: Sergey Senozhatsky 
Link: https://lore.kernel.org/r/5f743488-dc2a-4f19-bdda-cf50b9314832@paulmck-laptop
Signed-off-by: Boqun Feng 
Signed-off-by: Sasha Levin

printk: Fix signed integer overflow when defining LOG_BUF_LEN_MAX

2025-02-17T09:04:46+00:00

[ Upstream commit 3d6f83df8ff2d5de84b50377e4f0d45e25311c7a ]

Shifting 1 << 31 on a 32-bit int causes signed integer overflow, which
leads to undefined behavior. To prevent this, cast 1 to u32 before
performing the shift, ensuring well-defined behavior.

This change explicitly avoids any potential overflow by ensuring that
the shift occurs on an unsigned 32-bit integer.

Signed-off-by: Kuan-Wei Chiu 
Acked-by: Petr Mladek 
Link: https://lore.kernel.org/r/20240928113608.1438087-1-visitorckw@gmail.com
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

printk: Defer legacy printing when holding printk_cpu_sync

2025-02-08T08:56:57+00:00

[ Upstream commit 0161e2d6950fe66cf6ac1c10d945bae971f33667 ]

The documentation of printk_cpu_sync_get() clearly states
that the owner must never perform any activities where it waits
for a CPU. For legacy printing there can be spinning on the
console_lock and on the port lock. Therefore legacy printing
must be deferred when holding the printk_cpu_sync.

Note that in the case of emergency states, atomic consoles
are not prevented from printing when printk is deferred. This
is appropriate because they do not spin-wait indefinitely for
other CPUs.

Reported-by: Rik van Riel 
Closes: https://lore.kernel.org/r/20240715232052.73eb7fb1@imladris.surriel.com
Signed-off-by: John Ogness 
Fixes: 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and regs")
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20241209111746.192559-3-john.ogness@linutronix.de
Signed-off-by: Petr Mladek 
Signed-off-by: Sasha Levin

Merge tag 'drm-next-2024-09-19' of https://gitlab.freedesktop.org/drm/kernel

2024-09-19T08:18:15+00:00

Pull drm updates from Dave Airlie:
 "This adds a couple of patches outside the drm core, all should be
  acked appropriately, the string and pstore ones are the main ones that
  come to mind.

  Otherwise it's the usual drivers, xe is getting enabled by default on
  some new hardware, we've changed the device number handling to allow
  more devices, and we added some optional rust code to create QR codes
  in the panic handler, an idea first suggested I think 10 years ago :-)

  string:
   - add mem_is_zero()

  core:
   - support more device numbers
   - use XArray for minor ids
   - add backlight constants
   - Split dma fence array creation into alloc and arm

  fbdev:
   - remove usage of old fbdev hooks

  kms:
   - Add might_fault() to drm_modeset_lock priming
   - Add dynamic per-crtc vblank configuration support

  dma-buf:
   - docs cleanup

  buddy:
   - Add start address support for trim function

  printk:
   - pass description to kmsg_dump

  scheduler:
   - Remove full_recover from drm_sched_start

  ttm:
   - Make LRU walk restartable after dropping locks
   - Allow direct reclaim to allocate local memory

  panic:
   - add display QR code (in rust)

  displayport:
   - mst: GUID improvements

  bridge:
   - Silence error message on -EPROBE_DEFER
   - analogix: Clean aup
   - bridge-connector: Fix double free
   - lt6505: Disable interrupt when powered off
   - tc358767: Make default DP port preemphasis configurable
   - lt9611uxc: require DRM_BRIDGE_ATTACH_NO_CONNECTOR
   - anx7625: simplify OF array handling
   - dw-hdmi: simplify clock handling
   - lontium-lt8912b: fix mode validation
   - nwl-dsi: fix mode vsync/hsync polarity

  xe:
   - Enable LunarLake and Battlemage support
   - Introducing Xe2 ccs modifiers for integrated and discrete graphics
   - rename xe perf to xe observation
   - use wb caching on DGFX for system memory
   - add fence timeouts
   - Lunar Lake graphics/media/display workarounds
   - Battlemage workarounds
   - Battlemage GSC support
   - GSC and HuC fw updates for LL/BM
   - use dma_fence_chain_free
   - refactor hw engine lookup and mmio access
   - enable priority mem read for Xe2
   - Add first GuC BMG fw
   - fix dma-resv lock
   - Fix DGFX display suspend/resume
   - Use xe_managed for kernel BOs
   - Use reserved copy engine for user binds on faulting devices
   - Allow mixing dma-fence jobs and long-running faulting jobs
   - fix media TLB invalidation
   - fix rpm in TTM swapout path
   - track resources and VF state by PF

  i915:
   - Type-C programming fix for MTL+
   - FBC cleanup
   - Calc vblank delay more accurately
   - On DP MST, Enable LT fallback for UHBR<->non-UHBR rates
   - Fix DP LTTPR detection
   - limit relocations to INT_MAX
   - fix long hangs in buddy allocator on DG2/A380

  amdgpu:
   - Per-queue reset support
   - SDMA devcoredump support
   - DCN 4.0.1 updates
   - GFX12/VCN4/JPEG4 updates
   - Convert vbios embedded EDID to drm_edid
   - GFX9.3/9.4 devcoredump support
   - process isolation framework for GFX 9.4.3/4
   - take IOMMU mappings into account for P2P DMA

  amdkfd:
   - CRIU fixes
   - HMM fix
   - Enable process isolation support for GFX 9.4.3/4
   - Allow users to target recommended SDMA engines
   - KFD support for targetting queues on recommended SDMA engines

  radeon:
   - remove .load and drm_dev_alloc
   - Fix vbios embedded EDID size handling
   - Convert vbios embedded EDID to drm_edid
   - Use GEM references instead of TTM
   - r100 cp init cleanup
   - Fix potential overflows in evergreen CS offset tracking

  msm:
   - DPU:
      - implement DP/PHY mapping on SC8180X
      - Enable writeback on SM8150, SC8180X, SM6125, SM6350
   - DP:
      - Enable widebus on all relevant chipsets
      - MSM8998 HDMI support
   - GPU:
      - A642L speedbin support
      - A615/A306/A621 support
      - A7xx devcoredump support

  ast:
   - astdp: Support AST2600 with VGA
   - Clean up HPD
   - Fix timeout loop for DP link training
   - reorganize output code by type (VGA, DP, etc)
   - convert to struct drm_edid
   - fix BMC handling for all outputs

  exynos:
   - drop stale MAINTAINERS pattern
   - constify struct

  loongson:
   - use GEM refcount over TTM

  mgag200:
   - Improve BMC handling
   - Support VBLANK intterupts
   - transparently support BMC outputs

  nouveau:
   - Refactor and clean up internals
   - Use GEM refcount over TTM's

  gm12u320:
   - convert to struct drm_edid

  gma500:
   - update i2c terms

  lcdif:
   - pixel clock fix

  host1x:
   - fix syncpoint IRQ during resume
   - use iommu_paging_domain_alloc()

  imx:
   - ipuv3: convert to struct drm_edid

  omapdrm:
   - improve error handling
   - use common helper for_each_endpoint_of_node()

  panel:
   - add support for BOE TV101WUM-LL2 plus DT bindings
   - novatek-nt35950: improve error handling
   - nv3051d: improve error handling
   - panel-edp:
      - add support for BOE NE140WUM-N6G
      - revert support for SDC ATNA45AF01
   - visionox-vtdr6130:
      - improve error handling
      - use devm_regulator_bulk_get_const()
   - boe-th101mb31ig002:
      - Support for starry-er88577 MIPI-DSI panel plus DT
      - Fix porch parameter
   - edp: Support AOU B116XTN02.3, AUO B116XAN06.1, AOU B116XAT04.1, BOE
     NV140WUM-N41, BOE NV133WUM-N63, BOE NV116WHM-A4D, CMN N116BCA-EA2,
     CMN N116BCP-EA2, CSW MNB601LS1-4
   - himax-hx8394: Support Microchip AC40T08A MIPI Display panel plus DT
   - ilitek-ili9806e: Support Densitron DMT028VGHMCMI-1D TFT plus DT
   - jd9365da:
      - Support Melfas lmfbx101117480 MIPI-DSI panel plus DT
      - Refactor for code sharing
   - panel-edp: fix name for HKC MB116AN01
   - jd9365da: fix "exit sleep" commands
   - jdi-fhd-r63452: simplify error handling with DSI multi-style
     helpers
   - mantix-mlaf057we51: simplify error handling with DSI multi-style
     helpers
   - simple:
      - support Innolux G070ACE-LH3 plus DT bindings
      - support On Tat Industrial Company KD50G21-40NT-A1 plus DT
        bindings
   - st7701:
      - decouple DSI and DRM code
      - add SPI support
      - support Anbernic RG28XX plus DT bindings

  mediatek:
   - support alpha blending
   - remove cl in struct cmdq_pkt
   - ovl adaptor fix
   - add power domain binding for mediatek DPI controller

  renesas:
   - rz-du: add support for RZ/G2UL plus DT bindings

  rockchip:
   - Improve DP sink-capability reporting
   - dw_hdmi: Support 4k@60Hz
   - vop:
      - Support RGB display on Rockchip RK3066
      - Support 4096px width

  sti:
   - convert to struct drm_edid

  stm:
   - Avoid UAF wih managed plane and CRTC helpers
   - Fix module owner
   - Fix error handling in probe
   - Depend on COMMON_CLK
   - ltdc:
      - Fix transparency after disabling plane
      - Remove unused interrupt

  tegra:
   - gr3d: improve PM domain handling
   - convert to struct drm_edid
   - Call drm_atomic_helper_shutdown()

  vc4:
   - fix PM during detect
   - replace DRM_ERROR() with drm_error()
   - v3d: simplify clock retrieval

  v3d:
   - Clean up perfmon

  virtio:
   - add DRM capset"

* tag 'drm-next-2024-09-19' of https://gitlab.freedesktop.org/drm/kernel: (1326 commits)
  drm/xe: Fix missing conversion to xe_display_pm_runtime_resume
  drm/xe/xe2hpg: Add Wa_15016589081
  drm/xe: Don't keep stale pointer to bo->ggtt_node
  drm/xe: fix missing 'xe_vm_put'
  drm/xe: fix build warning with CONFIG_PM=n
  drm/xe: Suppress missing outer rpm protection warning
  drm/xe: prevent potential UAF in pf_provision_vf_ggtt()
  drm/amd/display: Add all planes on CRTC to state for overlay cursor
  drm/i915/bios: fix printk format width
  drm/i915/display: Fix BMG CCS modifiers
  drm/amdgpu: get rid of bogus includes of fdtable.h
  drm/amdkfd: CRIU fixes
  drm/amdgpu: fix a race in kfd_mem_export_dmabuf()
  drm: new helper: drm_gem_prime_handle_to_dmabuf()
  drm/amdgpu/atomfirmware: Silence UBSAN warning
  drm/amdgpu: Fix kdoc entry in 'amdgpu_vm_cpu_prepare'
  drm/amd/amdgpu: apply command submission parser for JPEG v1
  drm/amd/amdgpu: apply command submission parser for JPEG v2+
  drm/amd/pm: fix the pp_dpm_pcie issue on smu v14.0.2/3
  drm/amd/pm: update the features set on smu v14.0.2/3
  ...

Merge tag 'printk-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

2024-09-17T06:52:28+00:00

Pull printk updates from Petr Mladek:
"This is the "last" part of the support for the new nbcon consoles.
Where "nbcon" stays for "No Big console lock CONsoles" aka not under
the console_lock.

New callbacks are added to struct console:

- write_thread() for flushing nbcon consoles in task context.

- write_atomic() for flushing nbcon consoles in atomic context,
including NMI.

- con->device_lock() and device_unlock() for taking the driver
specific lock, for example, port->lock.

New printk-specific kthreads are created:

- per-console kthreads which get responsible for flushing normal
priority messages on nbcon consoles.

- thread which gets responsible for flushing normal priority messages
on all consoles when CONFIG_RT enabled.

The new callbacks are called under a special per-console lock which
has already been added back in v6.7. It allows to distinguish three
severities: normal, emergency, and panic. A context with a higher
priority could take over the ownership when it is safe even in the
middle of handling a record. The panic context could do it even when
it is not safe. But it is allowed only for the final desperate flush
before entering the infinite loop.

The new lock helps to flush the messages directly in emergency and
panic contexts. But it is not enough in all situations:

- console_lock() is still need for synchronization against boot
consoles.

- con->device_lock() is need for synchronization against other
operations on the same HW, e.g. serial port speed setting,
non-printk related read/write.

The dependency on con->device_lock() is mutual. Any code taking the
driver specific lock has to acquire the related nbcon console context
as well. For example, see the new uart_port_lock() API. It provides
the necessary synchronization against emergency and panic contexts
where the messages are flushed only under the new per-console lock.

Maybe surprisingly, a quite tricky part is the decision how to flush
the consoles in various situations. It has to take into account:

- message priority: normal, emergency, panic

- scheduling context: task, atomic, deferred_legacy

- registered consoles: boot, legacy, nbcon

- threads are running: early boot, suspend, shutdown, panic

- caller: printk(), pr_flush(), printk_flush_in_panic(),
console_unlock(), console_start(), ...

The primary decision is made in printk_get_console_flush_type(). It
creates a hint what the caller should do:

- flush nbcon consoles directly or via the kthread

- call the legacy loop (console_unlock()) directly or via irq_work

The existing behavior is preserved for the legacy consoles. The only
exception is that they are not longer flushed directly from printk()
in panic() before CPUs are stopped. But this blocking happens only
when at least one nbcon console is registered. The motivation is to
increase a chance to produce the crash dump. They legacy consoles
might create a deadlock in compare with nbcon consoles. The nbcon
console should allow to see the messages even when the crash dump
fails.

There are three possible ways how nbcon consoles are flushed:

- The per-nbcon-console kthread is responsible for flushing messages
added with the normal priority. This is the default mode.

- The legacy loop, aka console_unlock(), is used when there is still
a boot console registered. There is no easy way how to match an
early console driver with a nbcon console driver. And the
console_lock() provides the only reliable serialization at the
moment.

The legacy loop uses either con->write_atomic() or
con->write_thread() callbacks depending on whether it is allowed to
schedule. The atomic variant has to be used from printk().

- In other situations, the messages are flushed directly using
write_atomic() which can be called in any context, including NMI.
It is primary needed during early boot or shutdown, in emergency
situations, and panic.

The emergency priority is used by a code called within
nbcon_cpu_emergency_enter()/exit(). At the moment, it is used in four
situations: WARN(), Oops, lockdep, and RCU stall reports.

Finally, there is no nbcon console at the moment. It means that the
changes should _not_ modify the existing behavior. The only exception
is CONFIG_RT which would force offloading the legacy loop, for normal
priority context, into the dedicated kthread"

* tag 'printk-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (54 commits)
printk: Avoid false positive lockdep report for legacy printing
printk: nbcon: Assign nice -20 for printing threads
printk: Implement legacy printer kthread for PREEMPT_RT
tty: sysfs: Add nbcon support for 'active'
proc: Add nbcon support for /proc/consoles
proc: consoles: Add notation to c_start/c_stop
printk: nbcon: Show replay message on takeover
printk: Provide helper for message prepending
printk: nbcon: Rely on kthreads for normal operation
printk: nbcon: Use thread callback if in task context for legacy
printk: nbcon: Relocate nbcon_atomic_emit_one()
printk: nbcon: Introduce printer kthreads
printk: nbcon: Init @nbcon_seq to highest possible
printk: nbcon: Add context to usable() and emit()
printk: Flush console on unregister_console()
printk: Fail pr_flush() if before SYSTEM_SCHEDULING
printk: nbcon: Add function for printers to reacquire ownership
printk: nbcon: Use raw_cpu_ptr() instead of open coding
printk: Use the BITS_PER_LONG macro
lockdep: Mark emergency sections in lockdep splats
...

printk: Export match_devname_and_update_preferred_console()

2024-09-09T15:35:06+00:00

When building serial_base as a module, modpost fails with the following
error message:

  ERROR: modpost: "match_devname_and_update_preferred_console"
  [drivers/tty/serial/serial_base.ko] undefined!

Export the symbol to allow using it from modules.

Reported-by: kernel test robot 
Closes: https://lore.kernel.org/oe-kbuild-all/202409071312.qlwtTOS1-lkp@intel.com/
Fixes: 12c91cec3155 ("serial: core: Add serial_base_match_and_update_preferred_console()")
Signed-off-by: Yu Liao 
Link: https://lore.kernel.org/r/20240909075652.747370-1-liaoyu15@huawei.com
Signed-off-by: Petr Mladek

printk: Avoid false positive lockdep report for legacy printing

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

Legacy console printing from printk() caller context may invoke
the console driver from atomic context. This leads to a lockdep
splat because the console driver will acquire a sleeping lock
and the caller may already hold a spinning lock. This is noticed
by lockdep on !PREEMPT_RT configurations because it will lead to
a problem on PREEMPT_RT.

However, on PREEMPT_RT the printing path from atomic context is
always avoided and the console driver is always invoked from a
dedicated thread. Thus the lockdep splat on !PREEMPT_RT is a
false positive.

For !PREEMPT_RT override the lock-context before invoking the
console driver to avoid the false positive.

Do not override the lock-context for PREEMPT_RT in order to
allow lockdep to catch any real locking context issues related
to the write callback usage.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Link: https://lore.kernel.org/r/20240904120536.115780-18-john.ogness@linutronix.de
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