[PATCH v5 0/4] cleanup: Remove NULL check from unconditional guards

[Dmitry Ilvokhin <d@ilvokhin.com>]

Unconditional guard destructors have dead NULL checks. The lock operation in
the constructor would crash before the destructor ever runs with NULL.

- Patches 1-2 prepare guards that legitimately handle NULL.
- Patch 3 adds __nonnull_args() to guard constructors for compile-time
  enforcement.
- Patch 4 removes the dead checks.

As compiled by GCC-11 with defconfig on top of the locking/core:

    Total: Before=23889980, After=23834334, chg -0.23%

Changes in v5:

- Renamed __nonnull() attribute to __nonnull_args() to fix User Mode Linux
  build failures (kernel test robot).
- Dropped Acked-by tag from Miguel, since I renamed the attribute.

Changes in v4:

- Re-worded commit message paragraph about nonnull "compiler-enforced
  verification" (Miguel Ojeda).
- Fixed GCC documentation link for nonnull() attribute (Miguel Ojeda).
- Placed nonnull() before nonstring() in
  include/linux/compiler_attributes.h (Miguel Ojeda).
- Picked up tags, where appropriate.

Changes in v3:

- Audited usages of DEFINE_GUARD(), __DEFINE_UNLOCK_GUARD() and
  DEFINE_LOCK_GUARD_1() to make sure NULL check removal will work correctly
  (Peter Zijlstra).
- Moved NULL check into irqdesc_lock unlock expression (Peter Zijlstra).
- Added compiler-enforced nonnull() check for guard constructors.
- Converted nvdimm_bus guard to class.

Changes in v2:

- Expand commit message with detailed reasoning, why the proposed
  change is correct.
- Rebase on top of locking/core.

v4: https://lore.kernel.org/all/cover.1779286416.git.d@ilvokhin.com/
v3: https://lore.kernel.org/all/cover.1779116497.git.d@ilvokhin.com/
v2: https://lore.kernel.org/all/20260512071510.92451-1-d@ilvokhin.com/
v1: https://lore.kernel.org/all/20260427165037.205337-1-d@ilvokhin.com/

See also [1] for relevant discussion.

[1]: https://lore.kernel.org/all/afCS4d4YccQFtvpi@shell.ilvokhin.com/

Dmitry Ilvokhin (4):
  nvdimm: Convert nvdimm_bus guard to class
  genirq: Move NULL check into irqdesc_lock guard unlock expression
  cleanup: Annotate guard constructors with nonnull
  cleanup: Remove NULL check from unconditional guards

 drivers/nvdimm/nd.h                 | 7 +++++--
 include/linux/cleanup.h             | 8 +++++---
 include/linux/compiler_attributes.h | 9 +++++++++
 kernel/irq/internals.h              | 2 +-
 4 files changed, 20 insertions(+), 6 deletions(-)

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