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SubjectRe: [PATCH 2/2] mm: slub: use DEFINE_RAW_SPINLOCK init object_map_lock
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On 5/25/21 12:23 PM, Yejune Deng wrote:
> Use DEFINE_RAW_SPINLOCK instead of DEFINE_SPINLOCK object_map_lock
> that won't be preempted on mainline and PREEMPT_RT kernels.
>
> Signed-off-by: Yejune Deng <yejunedeng@gmail.com>

RT tree also has such patch, with IMHO more thorough description:

https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/tree/patches/0002-mm-slub-Make-object_map_lock-a-raw_spinlock_t.patch?h=linux-5.12.y-rt-patches

I was planning to include that in the next version of my series as that
will indeed be necessary.

> ---
> mm/slub.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index c2f63c3..995f3d0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -445,7 +445,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
>
> #ifdef CONFIG_SLUB_DEBUG
> static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
> -static DEFINE_SPINLOCK(object_map_lock);
> +static DEFINE_RAW_SPINLOCK(object_map_lock);
>
> #if IS_ENABLED(CONFIG_KUNIT)
> static bool slab_add_kunit_errors(void)
> @@ -481,7 +481,7 @@ static unsigned long *get_map(struct kmem_cache *s, struct page *page)
>
> VM_BUG_ON(!irqs_disabled());
>
> - spin_lock(&object_map_lock);
> + raw_spin_lock(&object_map_lock);
>
> bitmap_zero(object_map, page->objects);
>
> @@ -494,7 +494,7 @@ static unsigned long *get_map(struct kmem_cache *s, struct page *page)
> static void put_map(unsigned long *map) __releases(&object_map_lock)
> {
> VM_BUG_ON(map != object_map);
> - spin_unlock(&object_map_lock);
> + raw_spin_unlock(&object_map_lock);
> }
>
> static inline unsigned int size_from_object(struct kmem_cache *s)
>

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