Depending on the system configuration, the restricted pointer formatting
might call into the security subsystem which takes spinlocks, which
might sleep under PREEMPT_RT. As %pK is intended to be only used from
read handlers of virtual files, which always run in task context,
this should not be a problem in practice.
However, developers have used %pK before from atomic context without
realizing this restriction.

Add a lockdep annotation to unconditionally introduce a fake spinlock in
restricted_pointer(), so lockdep can detect misuse even if the current
test system configuration would not exhibit the issue.

---
Changes in v3:
- Use in_task() over its open-coded inverse.
  - Also switch the existing check over to it.
- Link to v2: https://patch.msgid.link/20260504-restricted-pointers-final-v2-0-4934933503e5@linutronix.de

Changes in v2:
- Use custom lock_map over might_sleep()
- Also assert IRQ context
- Link to v1: https://lore.kernel.org/r/20260317-restricted-pointers-final-v1-1-b4dca0ed6483@linutronix.de

To: Andrew Morton <akpm@linux-foundation.org>
To: Petr Mladek <pmladek@suse.com>
To: Steven Rostedt <rostedt@goodmis.org>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@redhat.com>
To: Will Deacon <will@kernel.org>
To: Boqun Feng <boqun@kernel.org>
To: Waiman Long <longman@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Clark Williams <clrkwllms@kernel.org>
To: Kees Cook <kees@kernel.org>
Cc: linux-kernel@vger.kernel.org
Cc: linux-rt-devel@lists.linux.dev
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>

---
Thomas Weißschuh (5):
      locking/lockdep: Add a helper to validate the locking context without a lock
      locking/lockdep: Add a guard for lock_map_acquire()
      lib/vsprintf: Validate spinlock context during restricted pointer formatting
      lib/vsprintf: Use in_task() for restricted pointer context check
      lib/vsprintf: Always check interrupt context restrictions

 include/linux/lockdep.h | 11 +++++++++++
 lib/vsprintf.c          | 13 ++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)
---
base-commit: 254f49634ee16a731174d2ae34bc50bd5f45e731
change-id: 20260107-restricted-pointers-final-cd24979fd752

Best regards,
--  
Thomas Weißschuh <thomas.weissschuh@linutronix.de>