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lockdep/selftests: Restore sched_rt_mutex state on PREEMPT_RT

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The WW-mutex selftests deliberately exercise failing lock paths. On
PREEMPT_RT, some of those paths enter the RT-mutex scheduler helpers.

The change referenced by the Fixes tag made those helpers track RT-mutex
scheduling state in current->sched_rt_mutex. The bit is normally cleared by
the matching post-schedule helper, but some WW-mutex selftests disable
the runtime debug_locks flag before that happens. With debug_locks cleared,
lockdep_assert() does not evaluate the expression that clears the bit,
leaving stale state for the next testcase.

With CONFIG_PREEMPT_RT=y and CONFIG_DEBUG_LOCKING_API_SELFTESTS=y, that
stale state produces warnings such as:

  WARNING: kernel/sched/core.c:7557 at rt_mutex_pre_schedule+0x26/0x2d
  RIP: 0010:rt_mutex_pre_schedule+0x26/0x2d

Save and restore current->sched_rt_mutex around each testcase, matching the
existing PREEMPT_RT cleanup for task-local migration and RCU state.

Fixes: d14f9e930b ("locking/rtmutex: Use rt_mutex specific scheduler helpers")
Assisted-by: Codex:gpt-5
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20260523185123.17482-3-kmehltretter@gmail.com
This commit is contained in:
Karl Mehltretter 2026-05-23 20:51:23 +02:00 committed by Peter Zijlstra
parent d8c897b20b
commit 06961d60a0
1 changed files with 3 additions and 0 deletions
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3
lib/locking-selftest.c
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@ -1433,6 +1433,7 @@ static void dotest(void (*testcase_fn)(void), int expected, int lockclass_mask)
#ifdef CONFIG_PREEMPT_RT
int saved_mgd_count = current->migration_disabled;
int saved_rcu_count = current->rcu_read_lock_nesting;
int saved_sched_rt_mutex = current->sched_rt_mutex;
#endif
WARN_ON(irqs_disabled());
@ -1469,6 +1470,8 @@ static void dotest(void (*testcase_fn)(void), int expected, int lockclass_mask)
preempt_count_set(saved_preempt_count);
#ifdef CONFIG_PREEMPT_RT
current->sched_rt_mutex = saved_sched_rt_mutex;
while (current->migration_disabled > saved_mgd_count)
migrate_enable();