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Subject[RFC v2 31/34] mm, slub: optionally save/restore irqs in slab_[un]lock()/
Date
For PREEMPT_RT we will need to disable irqs for this bit spinlock. As a
preparation, add a flags parameter, and an internal version that takes
additional bool parameter to control irq saving/restoring (the flags
parameter is compile-time unused if the bool is a constant false).

Convert ___cmpxchg_double_slab(), which also comes with the same bool
parameter, to use the internal version.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/slub.c | 49 +++++++++++++++++++++++++++++++------------------
1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index cfd5a7660375..6721169f816d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -353,18 +353,35 @@ static inline unsigned int oo_objects(struct kmem_cache_order_objects x)
/*
* Per slab locking using the pagelock
*/
-static __always_inline void slab_lock(struct page *page)
+static __always_inline void
+__slab_lock(struct page *page, unsigned long *flags, bool disable_irqs)
{
VM_BUG_ON_PAGE(PageTail(page), page);
+ if (disable_irqs)
+ local_irq_save(*flags);
bit_spin_lock(PG_locked, &page->flags);
}

-static __always_inline void slab_unlock(struct page *page)
+static __always_inline void
+__slab_unlock(struct page *page, unsigned long *flags, bool disable_irqs)
{
VM_BUG_ON_PAGE(PageTail(page), page);
+ if (disable_irqs)
+ local_irq_restore(*flags);
__bit_spin_unlock(PG_locked, &page->flags);
}

+static __always_inline void
+slab_lock(struct page *page, unsigned long *flags)
+{
+ __slab_lock(page, flags, false);
+}
+
+static __always_inline void slab_unlock(struct page *page, unsigned long *flags)
+{
+ __slab_unlock(page, flags, false);
+}
+
static inline bool ___cmpxchg_double_slab(struct kmem_cache *s, struct page *page,
void *freelist_old, unsigned long counters_old,
void *freelist_new, unsigned long counters_new,
@@ -384,21 +401,15 @@ static inline bool ___cmpxchg_double_slab(struct kmem_cache *s, struct page *pag
{
unsigned long flags;

- if (disable_irqs)
- local_irq_save(flags);
- slab_lock(page);
+ __slab_lock(page, &flags, disable_irqs);
if (page->freelist == freelist_old &&
page->counters == counters_old) {
page->freelist = freelist_new;
page->counters = counters_new;
- slab_unlock(page);
- if (disable_irqs)
- local_irq_restore(flags);
+ __slab_unlock(page, &flags, disable_irqs);
return true;
}
- slab_unlock(page);
- if (disable_irqs)
- local_irq_restore(flags);
+ __slab_unlock(page, &flags, disable_irqs);
}

cpu_relax();
@@ -1214,11 +1225,11 @@ static noinline int free_debug_processing(
struct kmem_cache_node *n = get_node(s, page_to_nid(page));
void *object = head;
int cnt = 0;
- unsigned long flags;
+ unsigned long flags, flags2;
int ret = 0;

spin_lock_irqsave(&n->list_lock, flags);
- slab_lock(page);
+ slab_lock(page, &flags2);

if (s->flags & SLAB_CONSISTENCY_CHECKS) {
if (!check_slab(s, page))
@@ -1251,7 +1262,7 @@ static noinline int free_debug_processing(
slab_err(s, page, "Bulk freelist count(%d) invalid(%d)\n",
bulk_cnt, cnt);

- slab_unlock(page);
+ slab_unlock(page, &flags2);
spin_unlock_irqrestore(&n->list_lock, flags);
if (!ret)
slab_fix(s, "Object at 0x%p not freed", object);
@@ -4007,9 +4018,10 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
void *addr = page_address(page);
unsigned long *map;
void *p;
+ unsigned long flags;

slab_err(s, page, text, s->name);
- slab_lock(page);
+ slab_lock(page, &flags);

map = get_map(s, page);
for_each_object(p, s, addr, page->objects) {
@@ -4020,7 +4032,7 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
}
}
put_map(map);
- slab_unlock(page);
+ slab_unlock(page, &flags);
#endif
}

@@ -4736,8 +4748,9 @@ static void validate_slab(struct kmem_cache *s, struct page *page,
{
void *p;
void *addr = page_address(page);
+ unsigned long flags;

- slab_lock(page);
+ slab_lock(page, &flags);

if (!check_slab(s, page) || !on_freelist(s, page, NULL))
goto unlock;
@@ -4752,7 +4765,7 @@ static void validate_slab(struct kmem_cache *s, struct page *page,
break;
}
unlock:
- slab_unlock(page);
+ slab_unlock(page, &flags);
}

static int validate_slab_node(struct kmem_cache *s,
--
2.31.1
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