arch_faults_on_old_pte() relies on the calling context being non-preemptible. CONFIG_PREEMPT_RT turns the PTE lock into a sleepable spinlock, which doesn't disable preemption once acquired, triggering the warning in arch_faults_on_old_pte(). It does however disable migration, ensuring the task remains on the same CPU during the entirety of the critical section, making the read of cpu_has_hw_af() safe and stable. Make arch_faults_on_old_pte() check cant_migrate() instead of preemptible(). Suggested-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx> Link: https://lore.kernel.org/r/20210811201354.1976839-5-valentin.schneider@xxxxxxx --- v3 -> v4: Dropped migratable(), reuse cant_migrate() (Sebastian) --- arch/arm64/include/asm/pgtable.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index c4ba047a82d2..3caf6346ea95 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -1001,7 +1001,8 @@ static inline void update_mmu_cache(struct vm_area_struct *vma, */ static inline bool arch_faults_on_old_pte(void) { - WARN_ON(preemptible()); + /* The register read below requires a stable CPU to make any sense */ + cant_migrate(); return !cpu_has_hw_af(); } -- 2.25.1
