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210ed9deff
Commit 1331e7a1bb
("rcu: Remove _rcu_barrier() dependency on
__stop_machine()") introduced slab_mutex -> cpu_hotplug.lock dependency
through kmem_cache_destroy() -> rcu_barrier() -> _rcu_barrier() ->
get_online_cpus().
Lockdep thinks that this might actually result in ABBA deadlock,
and reports it as below:
=== [ cut here ] ===
======================================================
[ INFO: possible circular locking dependency detected ]
3.6.0-rc5-00004-g0d8ee37 #143 Not tainted
-------------------------------------------------------
kworker/u:2/40 is trying to acquire lock:
(rcu_sched_state.barrier_mutex){+.+...}, at: [<ffffffff810f2126>] _rcu_barrier+0x26/0x1e0
but task is already holding lock:
(slab_mutex){+.+.+.}, at: [<ffffffff81176e15>] kmem_cache_destroy+0x45/0xe0
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (slab_mutex){+.+.+.}:
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff81558cb5>] cpuup_callback+0x2f/0xbe
[<ffffffff81564b83>] notifier_call_chain+0x93/0x140
[<ffffffff81076f89>] __raw_notifier_call_chain+0x9/0x10
[<ffffffff8155719d>] _cpu_up+0xba/0x14e
[<ffffffff815572ed>] cpu_up+0xbc/0x117
[<ffffffff81ae05e3>] smp_init+0x6b/0x9f
[<ffffffff81ac47d6>] kernel_init+0x147/0x1dc
[<ffffffff8156ab44>] kernel_thread_helper+0x4/0x10
-> #1 (cpu_hotplug.lock){+.+.+.}:
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff81049197>] get_online_cpus+0x37/0x50
[<ffffffff810f21bb>] _rcu_barrier+0xbb/0x1e0
[<ffffffff810f22f0>] rcu_barrier_sched+0x10/0x20
[<ffffffff810f2309>] rcu_barrier+0x9/0x10
[<ffffffff8118c129>] deactivate_locked_super+0x49/0x90
[<ffffffff8118cc01>] deactivate_super+0x61/0x70
[<ffffffff811aaaa7>] mntput_no_expire+0x127/0x180
[<ffffffff811ab49e>] sys_umount+0x6e/0xd0
[<ffffffff81569979>] system_call_fastpath+0x16/0x1b
-> #0 (rcu_sched_state.barrier_mutex){+.+...}:
[<ffffffff810adb4e>] check_prev_add+0x3de/0x440
[<ffffffff810ae1e2>] validate_chain+0x632/0x720
[<ffffffff810ae5d9>] __lock_acquire+0x309/0x530
[<ffffffff810ae921>] lock_acquire+0x121/0x190
[<ffffffff8155d4cc>] __mutex_lock_common+0x5c/0x450
[<ffffffff8155d9ee>] mutex_lock_nested+0x3e/0x50
[<ffffffff810f2126>] _rcu_barrier+0x26/0x1e0
[<ffffffff810f22f0>] rcu_barrier_sched+0x10/0x20
[<ffffffff810f2309>] rcu_barrier+0x9/0x10
[<ffffffff81176ea1>] kmem_cache_destroy+0xd1/0xe0
[<ffffffffa04c3154>] nf_conntrack_cleanup_net+0xe4/0x110 [nf_conntrack]
[<ffffffffa04c31aa>] nf_conntrack_cleanup+0x2a/0x70 [nf_conntrack]
[<ffffffffa04c42ce>] nf_conntrack_net_exit+0x5e/0x80 [nf_conntrack]
[<ffffffff81454b79>] ops_exit_list+0x39/0x60
[<ffffffff814551ab>] cleanup_net+0xfb/0x1b0
[<ffffffff8106917b>] process_one_work+0x26b/0x4c0
[<ffffffff81069f3e>] worker_thread+0x12e/0x320
[<ffffffff8106f73e>] kthread+0x9e/0xb0
[<ffffffff8156ab44>] kernel_thread_helper+0x4/0x10
other info that might help us debug this:
Chain exists of:
rcu_sched_state.barrier_mutex --> cpu_hotplug.lock --> slab_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(slab_mutex);
lock(cpu_hotplug.lock);
lock(slab_mutex);
lock(rcu_sched_state.barrier_mutex);
*** DEADLOCK ***
=== [ cut here ] ===
This is actually a false positive. Lockdep has no way of knowing the fact
that the ABBA can actually never happen, because of special semantics of
cpu_hotplug.refcount and its handling in cpu_hotplug_begin(); the mutual
exclusion there is not achieved through mutex, but through
cpu_hotplug.refcount.
The "neither cpu_up() nor cpu_down() will proceed past cpu_hotplug_begin()
until everyone who called get_online_cpus() will call put_online_cpus()"
semantics is totally invisible to lockdep.
This patch therefore moves the unlock of slab_mutex so that rcu_barrier()
is being called with it unlocked. It has two advantages:
- it slightly reduces hold time of slab_mutex; as it's used to protect
the cachep list, it's not necessary to hold it over kmem_cache_free()
call any more
- it silences the lockdep false positive warning, as it avoids lockdep ever
learning about slab_mutex -> cpu_hotplug.lock dependency
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
195 lines
4.3 KiB
C
195 lines
4.3 KiB
C
/*
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* Slab allocator functions that are independent of the allocator strategy
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*
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* (C) 2012 Christoph Lameter <cl@linux.com>
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*/
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#include <linux/slab.h>
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#include <linux/mm.h>
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#include <linux/poison.h>
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#include <linux/interrupt.h>
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#include <linux/memory.h>
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#include <linux/compiler.h>
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#include <linux/module.h>
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#include <linux/cpu.h>
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#include <linux/uaccess.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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#include <asm/page.h>
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#include "slab.h"
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enum slab_state slab_state;
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LIST_HEAD(slab_caches);
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DEFINE_MUTEX(slab_mutex);
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struct kmem_cache *kmem_cache;
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#ifdef CONFIG_DEBUG_VM
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static int kmem_cache_sanity_check(const char *name, size_t size)
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{
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struct kmem_cache *s = NULL;
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if (!name || in_interrupt() || size < sizeof(void *) ||
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size > KMALLOC_MAX_SIZE) {
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pr_err("kmem_cache_create(%s) integrity check failed\n", name);
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return -EINVAL;
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}
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list_for_each_entry(s, &slab_caches, list) {
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char tmp;
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int res;
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/*
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* This happens when the module gets unloaded and doesn't
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* destroy its slab cache and no-one else reuses the vmalloc
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* area of the module. Print a warning.
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*/
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res = probe_kernel_address(s->name, tmp);
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if (res) {
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pr_err("Slab cache with size %d has lost its name\n",
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s->object_size);
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continue;
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}
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if (!strcmp(s->name, name)) {
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pr_err("%s (%s): Cache name already exists.\n",
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__func__, name);
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dump_stack();
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s = NULL;
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return -EINVAL;
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}
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}
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WARN_ON(strchr(name, ' ')); /* It confuses parsers */
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return 0;
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}
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#else
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static inline int kmem_cache_sanity_check(const char *name, size_t size)
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{
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return 0;
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}
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#endif
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/*
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* kmem_cache_create - Create a cache.
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* @name: A string which is used in /proc/slabinfo to identify this cache.
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* @size: The size of objects to be created in this cache.
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* @align: The required alignment for the objects.
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* @flags: SLAB flags
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* @ctor: A constructor for the objects.
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*
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* Returns a ptr to the cache on success, NULL on failure.
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* Cannot be called within a interrupt, but can be interrupted.
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* The @ctor is run when new pages are allocated by the cache.
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*
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* The flags are
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*
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* %SLAB_POISON - Poison the slab with a known test pattern (a5a5a5a5)
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* to catch references to uninitialised memory.
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*
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* %SLAB_RED_ZONE - Insert `Red' zones around the allocated memory to check
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* for buffer overruns.
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*
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* %SLAB_HWCACHE_ALIGN - Align the objects in this cache to a hardware
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* cacheline. This can be beneficial if you're counting cycles as closely
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* as davem.
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*/
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struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align,
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unsigned long flags, void (*ctor)(void *))
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{
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struct kmem_cache *s = NULL;
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int err = 0;
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get_online_cpus();
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mutex_lock(&slab_mutex);
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if (!kmem_cache_sanity_check(name, size) == 0)
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goto out_locked;
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s = __kmem_cache_alias(name, size, align, flags, ctor);
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if (s)
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goto out_locked;
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s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL);
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if (s) {
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s->object_size = s->size = size;
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s->align = align;
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s->ctor = ctor;
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s->name = kstrdup(name, GFP_KERNEL);
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if (!s->name) {
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kmem_cache_free(kmem_cache, s);
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err = -ENOMEM;
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goto out_locked;
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}
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err = __kmem_cache_create(s, flags);
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if (!err) {
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s->refcount = 1;
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list_add(&s->list, &slab_caches);
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} else {
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kfree(s->name);
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kmem_cache_free(kmem_cache, s);
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}
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} else
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err = -ENOMEM;
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out_locked:
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mutex_unlock(&slab_mutex);
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put_online_cpus();
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if (err) {
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if (flags & SLAB_PANIC)
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panic("kmem_cache_create: Failed to create slab '%s'. Error %d\n",
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name, err);
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else {
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printk(KERN_WARNING "kmem_cache_create(%s) failed with error %d",
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name, err);
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dump_stack();
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}
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return NULL;
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}
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return s;
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}
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EXPORT_SYMBOL(kmem_cache_create);
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void kmem_cache_destroy(struct kmem_cache *s)
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{
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get_online_cpus();
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mutex_lock(&slab_mutex);
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s->refcount--;
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if (!s->refcount) {
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list_del(&s->list);
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if (!__kmem_cache_shutdown(s)) {
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mutex_unlock(&slab_mutex);
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if (s->flags & SLAB_DESTROY_BY_RCU)
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rcu_barrier();
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kfree(s->name);
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kmem_cache_free(kmem_cache, s);
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} else {
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list_add(&s->list, &slab_caches);
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mutex_unlock(&slab_mutex);
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printk(KERN_ERR "kmem_cache_destroy %s: Slab cache still has objects\n",
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s->name);
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dump_stack();
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}
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} else {
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mutex_unlock(&slab_mutex);
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}
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put_online_cpus();
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}
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EXPORT_SYMBOL(kmem_cache_destroy);
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int slab_is_available(void)
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{
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return slab_state >= UP;
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}
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