From 3a01af828138041eb4bd27403ad3bd25f8e89790 Mon Sep 17 00:00:00 2001 From: Brendan Jackman Date: Fri, 3 Jul 2026 12:31:58 +0000 Subject: [PATCH] mm: factor out can_spin_trylock() Deduplicate checks for whether the current context is safe for spin_trylock(). Does this function really belong in mm/internal.h or is it generic? Not sure. If someone ends up duplicating this logic elsewhere in the kernel, that would be a shame. But if it goes in some generic header, someone treats it as documentation about where it's guaranteed safe to spin_trylock(), and then it emerges that there are other subtle preconditions that didn't affect the mm usecase, that would be worse. So, just be conservative and keep it local. Link: https://lore.kernel.org/20260703-alloc-trylock-v5-18-c87b714e19d3@google.com Signed-off-by: Brendan Jackman Suggested-by: Harry Yoo Link: https://lore.kernel.org/all/397859cb-b127-4cc6-9c71-044afc99bf0c@kernel.org/ Reviewed-by: Vlastimil Babka (SUSE) Reviewed-by: Harry Yoo (Oracle) Reviewed-by: Zi Yan Signed-off-by: Andrew Morton --- mm/internal.h | 23 +++++++++++++++++++++++ mm/page_alloc.c | 17 +---------------- mm/slub.c | 10 +--------- 3 files changed, 25 insertions(+), 25 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index ffa72bd31708..841c27611627 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1713,4 +1713,27 @@ static inline void mm_prepare_for_swap_entries(struct mm_struct *mm) } } +static inline bool can_spin_trylock(void) +{ + /* + * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is + * unsafe in NMI. If spin_trylock() is called from hard IRQ the current + * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will + * mark the task as the owner of another rt_spin_lock which will + * confuse PI logic, so return immediately if called from hard IRQ or + * NMI. + * + * Note, irqs_disabled() case is ok. spin_trylock() can be called + * from raw_spin_lock_irqsave region. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) + return false; + + /* On UP, spin_trylock() always succeeds even when it is locked */ + if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) + return false; + + return true; +} + #endif /* __MM_INTERNAL_H */ diff --git a/mm/page_alloc.c b/mm/page_alloc.c index c3b246e67ed1..a63733dac659 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5291,22 +5291,7 @@ static inline bool alloc_order_allowed(gfp_t gfp, unsigned int order, static inline bool alloc_nolock_allowed(void) { - /* - * In PREEMPT_RT spin_trylock() will call raw_spin_lock() which is - * unsafe in NMI. If spin_trylock() is called from hard IRQ the current - * task may be waiting for one rt_spin_lock, but rt_spin_trylock() will - * mark the task as the owner of another rt_spin_lock which will - * confuse PI logic, so return immediately if called from hard IRQ or - * NMI. - * - * Note, irqs_disabled() case is ok. This function can be called - * from raw_spin_lock_irqsave region. - */ - if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) - return false; - - /* On UP, spin_trylock() always succeeds even when it is locked */ - if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) + if (!can_spin_trylock()) return false; /* Bailout, since _deferred_grow_zone() needs to take a lock */ diff --git a/mm/slub.c b/mm/slub.c index 85599d227b9b..422bc3e12c02 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5380,15 +5380,7 @@ static void *__kmalloc_nolock_noprof(DECL_TOKEN_PARAMS(size, token), gfp_t gfp_f if (unlikely(!size)) return ZERO_SIZE_PTR; - /* - * See the comment for the same check in - * alloc_frozen_pages_nolock_noprof() - */ - if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) - return NULL; - - /* On UP, spin_trylock() always succeeds even when it is locked */ - if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) + if (!can_spin_trylock()) return NULL; retry: