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mm: factor out can_spin_trylock()

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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 <jackmanb@google.com>
Suggested-by: Harry Yoo <harry@kernel.org>
Link: https://lore.kernel.org/all/397859cb-b127-4cc6-9c71-044afc99bf0c@kernel.org/
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Brendan Jackman 2026-07-03 12:31:58 +00:00 committed by Andrew Morton
parent 5df11ba0eb
commit 3a01af8281
3 changed files with 25 additions and 25 deletions
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23
mm/internal.h
View File

@ -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 */

17
mm/page_alloc.c
View File

@ -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 */

10
mm/slub.c
View File

@ -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: