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Subject[PATCH 2/3] mm: avoid slub allocation while holding list_lock
From
If we are already under list_lock, don't call kmalloc(). Otherwise we
will run into deadlock because kmalloc() also tries to grab the same
lock.

Instead, statically allocate bitmap in struct kmem_cache_node. Given
currently page->objects has 15 bits, we bloat the per-node struct by
4K. So we waste some memory but only do so when slub debug is on.

WARNING: possible recursive locking detected
--------------------------------------------
mount-encrypted/4921 is trying to acquire lock:
(&(&n->list_lock)->rlock){-.-.}, at: ___slab_alloc+0x104/0x437

but task is already holding lock:
(&(&n->list_lock)->rlock){-.-.}, at: __kmem_cache_shutdown+0x81/0x3cb

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&(&n->list_lock)->rlock);
lock(&(&n->list_lock)->rlock);

*** DEADLOCK ***

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
include/linux/slub_def.h | 4 ++++
mm/slab.h | 1 +
mm/slub.c | 44 ++++++++++++++--------------------------
3 files changed, 20 insertions(+), 29 deletions(-)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index d2153789bd9f..719d43574360 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -9,6 +9,10 @@
*/
#include <linux/kobject.h>

+#define OO_SHIFT 15
+#define OO_MASK ((1 << OO_SHIFT) - 1)
+#define MAX_OBJS_PER_PAGE 32767 /* since page.objects is u15 */
+
enum stat_item {
ALLOC_FASTPATH, /* Allocation from cpu slab */
ALLOC_SLOWPATH, /* Allocation by getting a new cpu slab */
diff --git a/mm/slab.h b/mm/slab.h
index 9057b8056b07..2d8639835db1 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -556,6 +556,7 @@ struct kmem_cache_node {
atomic_long_t nr_slabs;
atomic_long_t total_objects;
struct list_head full;
+ unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
#endif
#endif

diff --git a/mm/slub.c b/mm/slub.c
index 62053ceb4464..f28072c9f2ce 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -187,10 +187,6 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
*/
#define DEBUG_METADATA_FLAGS (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER)

-#define OO_SHIFT 15
-#define OO_MASK ((1 << OO_SHIFT) - 1)
-#define MAX_OBJS_PER_PAGE 32767 /* since page.objects is u15 */
-
/* Internal SLUB flags */
/* Poison object */
#define __OBJECT_POISON ((slab_flags_t __force)0x80000000U)
@@ -454,6 +450,8 @@ static void get_map(struct kmem_cache *s, struct page *page, unsigned long *map)
void *p;
void *addr = page_address(page);

+ bitmap_zero(map, page->objects);
+
for (p = page->freelist; p; p = get_freepointer(s, p))
set_bit(slab_index(p, s, addr), map);
}
@@ -3680,14 +3678,12 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
}

static void list_slab_objects(struct kmem_cache *s, struct page *page,
- const char *text)
+ unsigned long *map, const char *text)
{
#ifdef CONFIG_SLUB_DEBUG
void *addr = page_address(page);
void *p;
- unsigned long *map = bitmap_zalloc(page->objects, GFP_ATOMIC);
- if (!map)
- return;
+
slab_err(s, page, text, s->name);
slab_lock(page);

@@ -3699,8 +3695,8 @@ static void list_slab_objects(struct kmem_cache *s, struct page *page,
print_tracking(s, p);
}
}
+
slab_unlock(page);
- bitmap_free(map);
#endif
}

@@ -3721,7 +3717,7 @@ static void free_partial(struct kmem_cache *s, struct kmem_cache_node *n)
remove_partial(n, page);
list_add(&page->slab_list, &discard);
} else {
- list_slab_objects(s, page,
+ list_slab_objects(s, page, n->object_map,
"Objects remaining in %s on __kmem_cache_shutdown()");
}
}
@@ -4397,7 +4393,6 @@ static int validate_slab(struct kmem_cache *s, struct page *page,
return 0;

/* Now we know that a valid freelist exists */
- bitmap_zero(map, page->objects);

get_map(s, page, map);
for_each_object(p, s, addr, page->objects) {
@@ -4422,7 +4417,7 @@ static void validate_slab_slab(struct kmem_cache *s, struct page *page,
}

static int validate_slab_node(struct kmem_cache *s,
- struct kmem_cache_node *n, unsigned long *map)
+ struct kmem_cache_node *n)
{
unsigned long count = 0;
struct page *page;
@@ -4431,7 +4426,7 @@ static int validate_slab_node(struct kmem_cache *s,
spin_lock_irqsave(&n->list_lock, flags);

list_for_each_entry(page, &n->partial, slab_list) {
- validate_slab_slab(s, page, map);
+ validate_slab_slab(s, page, n->object_map);
count++;
}
if (count != n->nr_partial)
@@ -4442,7 +4437,7 @@ static int validate_slab_node(struct kmem_cache *s,
goto out;

list_for_each_entry(page, &n->full, slab_list) {
- validate_slab_slab(s, page, map);
+ validate_slab_slab(s, page, n->object_map);
count++;
}
if (count != atomic_long_read(&n->nr_slabs))
@@ -4459,15 +4454,11 @@ static long validate_slab_cache(struct kmem_cache *s)
int node;
unsigned long count = 0;
struct kmem_cache_node *n;
- unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);
-
- if (!map)
- return -ENOMEM;

flush_all(s);
for_each_kmem_cache_node(s, node, n)
- count += validate_slab_node(s, n, map);
- bitmap_free(map);
+ count += validate_slab_node(s, n);
+
return count;
}
/*
@@ -4603,9 +4594,7 @@ static void process_slab(struct loc_track *t, struct kmem_cache *s,
void *addr = page_address(page);
void *p;

- bitmap_zero(map, page->objects);
get_map(s, page, map);
-
for_each_object(p, s, addr, page->objects)
if (!test_bit(slab_index(p, s, addr), map))
add_location(t, s, get_track(s, p, alloc));
@@ -4619,11 +4608,9 @@ static int list_locations(struct kmem_cache *s, char *buf,
struct loc_track t = { 0, 0, NULL };
int node;
struct kmem_cache_node *n;
- unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL);

- if (!map || !alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
- GFP_KERNEL)) {
- bitmap_free(map);
+ if (!alloc_loc_track(&t, PAGE_SIZE / sizeof(struct location),
+ GFP_KERNEL)) {
return sprintf(buf, "Out of memory\n");
}
/* Push back cpu slabs */
@@ -4638,9 +4625,9 @@ static int list_locations(struct kmem_cache *s, char *buf,

spin_lock_irqsave(&n->list_lock, flags);
list_for_each_entry(page, &n->partial, slab_list)
- process_slab(&t, s, page, alloc, map);
+ process_slab(&t, s, page, alloc, n->object_map);
list_for_each_entry(page, &n->full, slab_list)
- process_slab(&t, s, page, alloc, map);
+ process_slab(&t, s, page, alloc, n->object_map);
spin_unlock_irqrestore(&n->list_lock, flags);
}

@@ -4689,7 +4676,6 @@ static int list_locations(struct kmem_cache *s, char *buf,
}

free_loc_track(&t);
- bitmap_free(map);
if (!t.count)
len += sprintf(buf, "No data\n");
return len;
--
2.23.0.162.g0b9fbb3734-goog
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