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![Greg Thelen](/assets/img/avatar_default.png)
Per memcg slab accounting and kasan have a problem with kmem_cache destruction. - kmem_cache_create() allocates a kmem_cache, which is used for allocations from processes running in root (top) memcg. - Processes running in non root memcg and allocating with either __GFP_ACCOUNT or from a SLAB_ACCOUNT cache use a per memcg kmem_cache. - Kasan catches use-after-free by having kfree() and kmem_cache_free() defer freeing of objects. Objects are placed in a quarantine. - kmem_cache_destroy() destroys root and non root kmem_caches. It takes care to drain the quarantine of objects from the root memcg's kmem_cache, but ignores objects associated with non root memcg. This causes leaks because quarantined per memcg objects refer to per memcg kmem cache being destroyed. To see the problem: 1) create a slab cache with kmem_cache_create(,,,SLAB_ACCOUNT,) 2) from non root memcg, allocate and free a few objects from cache 3) dispose of the cache with kmem_cache_destroy() kmem_cache_destroy() will trigger a "Slab cache still has objects" warning indicating that the per memcg kmem_cache structure was leaked. Fix the leak by draining kasan quarantined objects allocated from non root memcg. Racing memcg deletion is tricky, but handled. kmem_cache_destroy() => shutdown_memcg_caches() => __shutdown_memcg_cache() => shutdown_cache() flushes per memcg quarantined objects, even if that memcg has been rmdir'd and gone through memcg_deactivate_kmem_caches(). This leak only affects destroyed SLAB_ACCOUNT kmem caches when kasan is enabled. So I don't think it's worth patching stable kernels. Link: http://lkml.kernel.org/r/1482257462-36948-1-git-send-email-gthelen@google.com Signed-off-by: Greg Thelen <gthelen@google.com> Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com> Acked-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Alexander Potapenko <glider@google.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: David Rientjes <rientjes@google.com> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
291 lines
7.2 KiB
C
291 lines
7.2 KiB
C
/*
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* KASAN quarantine.
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*
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* Author: Alexander Potapenko <glider@google.com>
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* Copyright (C) 2016 Google, Inc.
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*
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* Based on code by Dmitry Chernenkov.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* version 2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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*/
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#include <linux/gfp.h>
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#include <linux/hash.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/percpu.h>
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#include <linux/printk.h>
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#include <linux/shrinker.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/types.h>
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#include "../slab.h"
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#include "kasan.h"
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/* Data structure and operations for quarantine queues. */
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/*
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* Each queue is a signle-linked list, which also stores the total size of
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* objects inside of it.
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*/
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struct qlist_head {
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struct qlist_node *head;
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struct qlist_node *tail;
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size_t bytes;
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};
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#define QLIST_INIT { NULL, NULL, 0 }
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static bool qlist_empty(struct qlist_head *q)
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{
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return !q->head;
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}
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static void qlist_init(struct qlist_head *q)
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{
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q->head = q->tail = NULL;
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q->bytes = 0;
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}
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static void qlist_put(struct qlist_head *q, struct qlist_node *qlink,
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size_t size)
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{
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if (unlikely(qlist_empty(q)))
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q->head = qlink;
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else
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q->tail->next = qlink;
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q->tail = qlink;
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qlink->next = NULL;
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q->bytes += size;
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}
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static void qlist_move_all(struct qlist_head *from, struct qlist_head *to)
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{
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if (unlikely(qlist_empty(from)))
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return;
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if (qlist_empty(to)) {
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*to = *from;
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qlist_init(from);
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return;
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}
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to->tail->next = from->head;
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to->tail = from->tail;
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to->bytes += from->bytes;
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qlist_init(from);
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}
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#define QUARANTINE_PERCPU_SIZE (1 << 20)
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#define QUARANTINE_BATCHES \
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(1024 > 4 * CONFIG_NR_CPUS ? 1024 : 4 * CONFIG_NR_CPUS)
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/*
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* The object quarantine consists of per-cpu queues and a global queue,
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* guarded by quarantine_lock.
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*/
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static DEFINE_PER_CPU(struct qlist_head, cpu_quarantine);
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/* Round-robin FIFO array of batches. */
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static struct qlist_head global_quarantine[QUARANTINE_BATCHES];
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static int quarantine_head;
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static int quarantine_tail;
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/* Total size of all objects in global_quarantine across all batches. */
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static unsigned long quarantine_size;
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static DEFINE_SPINLOCK(quarantine_lock);
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/* Maximum size of the global queue. */
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static unsigned long quarantine_max_size;
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/*
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* Target size of a batch in global_quarantine.
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* Usually equal to QUARANTINE_PERCPU_SIZE unless we have too much RAM.
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*/
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static unsigned long quarantine_batch_size;
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/*
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* The fraction of physical memory the quarantine is allowed to occupy.
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* Quarantine doesn't support memory shrinker with SLAB allocator, so we keep
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* the ratio low to avoid OOM.
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*/
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#define QUARANTINE_FRACTION 32
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static struct kmem_cache *qlink_to_cache(struct qlist_node *qlink)
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{
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return virt_to_head_page(qlink)->slab_cache;
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}
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static void *qlink_to_object(struct qlist_node *qlink, struct kmem_cache *cache)
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{
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struct kasan_free_meta *free_info =
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container_of(qlink, struct kasan_free_meta,
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quarantine_link);
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return ((void *)free_info) - cache->kasan_info.free_meta_offset;
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}
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static void qlink_free(struct qlist_node *qlink, struct kmem_cache *cache)
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{
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void *object = qlink_to_object(qlink, cache);
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unsigned long flags;
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if (IS_ENABLED(CONFIG_SLAB))
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local_irq_save(flags);
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___cache_free(cache, object, _THIS_IP_);
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if (IS_ENABLED(CONFIG_SLAB))
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local_irq_restore(flags);
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}
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static void qlist_free_all(struct qlist_head *q, struct kmem_cache *cache)
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{
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struct qlist_node *qlink;
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if (unlikely(qlist_empty(q)))
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return;
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qlink = q->head;
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while (qlink) {
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struct kmem_cache *obj_cache =
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cache ? cache : qlink_to_cache(qlink);
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struct qlist_node *next = qlink->next;
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qlink_free(qlink, obj_cache);
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qlink = next;
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}
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qlist_init(q);
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}
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void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache)
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{
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unsigned long flags;
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struct qlist_head *q;
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struct qlist_head temp = QLIST_INIT;
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local_irq_save(flags);
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q = this_cpu_ptr(&cpu_quarantine);
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qlist_put(q, &info->quarantine_link, cache->size);
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if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE))
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qlist_move_all(q, &temp);
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local_irq_restore(flags);
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if (unlikely(!qlist_empty(&temp))) {
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spin_lock_irqsave(&quarantine_lock, flags);
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WRITE_ONCE(quarantine_size, quarantine_size + temp.bytes);
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qlist_move_all(&temp, &global_quarantine[quarantine_tail]);
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if (global_quarantine[quarantine_tail].bytes >=
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READ_ONCE(quarantine_batch_size)) {
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int new_tail;
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new_tail = quarantine_tail + 1;
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if (new_tail == QUARANTINE_BATCHES)
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new_tail = 0;
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if (new_tail != quarantine_head)
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quarantine_tail = new_tail;
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}
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spin_unlock_irqrestore(&quarantine_lock, flags);
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}
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}
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void quarantine_reduce(void)
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{
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size_t total_size, new_quarantine_size, percpu_quarantines;
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unsigned long flags;
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struct qlist_head to_free = QLIST_INIT;
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if (likely(READ_ONCE(quarantine_size) <=
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READ_ONCE(quarantine_max_size)))
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return;
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spin_lock_irqsave(&quarantine_lock, flags);
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/*
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* Update quarantine size in case of hotplug. Allocate a fraction of
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* the installed memory to quarantine minus per-cpu queue limits.
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*/
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total_size = (READ_ONCE(totalram_pages) << PAGE_SHIFT) /
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QUARANTINE_FRACTION;
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percpu_quarantines = QUARANTINE_PERCPU_SIZE * num_online_cpus();
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new_quarantine_size = (total_size < percpu_quarantines) ?
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0 : total_size - percpu_quarantines;
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WRITE_ONCE(quarantine_max_size, new_quarantine_size);
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/* Aim at consuming at most 1/2 of slots in quarantine. */
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WRITE_ONCE(quarantine_batch_size, max((size_t)QUARANTINE_PERCPU_SIZE,
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2 * total_size / QUARANTINE_BATCHES));
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if (likely(quarantine_size > quarantine_max_size)) {
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qlist_move_all(&global_quarantine[quarantine_head], &to_free);
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WRITE_ONCE(quarantine_size, quarantine_size - to_free.bytes);
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quarantine_head++;
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if (quarantine_head == QUARANTINE_BATCHES)
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quarantine_head = 0;
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}
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spin_unlock_irqrestore(&quarantine_lock, flags);
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qlist_free_all(&to_free, NULL);
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}
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static void qlist_move_cache(struct qlist_head *from,
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struct qlist_head *to,
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struct kmem_cache *cache)
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{
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struct qlist_node *curr;
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if (unlikely(qlist_empty(from)))
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return;
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curr = from->head;
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qlist_init(from);
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while (curr) {
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struct qlist_node *next = curr->next;
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struct kmem_cache *obj_cache = qlink_to_cache(curr);
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if (obj_cache == cache)
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qlist_put(to, curr, obj_cache->size);
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else
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qlist_put(from, curr, obj_cache->size);
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curr = next;
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}
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}
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static void per_cpu_remove_cache(void *arg)
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{
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struct kmem_cache *cache = arg;
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struct qlist_head to_free = QLIST_INIT;
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struct qlist_head *q;
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q = this_cpu_ptr(&cpu_quarantine);
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qlist_move_cache(q, &to_free, cache);
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qlist_free_all(&to_free, cache);
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}
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/* Free all quarantined objects belonging to cache. */
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void quarantine_remove_cache(struct kmem_cache *cache)
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{
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unsigned long flags, i;
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struct qlist_head to_free = QLIST_INIT;
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on_each_cpu(per_cpu_remove_cache, cache, 1);
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spin_lock_irqsave(&quarantine_lock, flags);
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for (i = 0; i < QUARANTINE_BATCHES; i++)
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qlist_move_cache(&global_quarantine[i], &to_free, cache);
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spin_unlock_irqrestore(&quarantine_lock, flags);
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qlist_free_all(&to_free, cache);
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}
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