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![Hou Tao](/assets/img/avatar_default.png)
If there are pending rcu callback, free_mem_alloc() will use rcu_barrier_tasks_trace() and rcu_barrier() to wait for the pending __free_rcu_tasks_trace() and __free_rcu() callback. If rcu_trace_implies_rcu_gp() is true, there will be no pending __free_rcu(), so it will be OK to skip rcu_barrier() as well. Acked-by: Yonghong Song <yhs@fb.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/r/20221209010947.3130477-3-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
677 lines
18 KiB
C
677 lines
18 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright (c) 2022 Meta Platforms, Inc. and affiliates. */
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#include <linux/mm.h>
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#include <linux/llist.h>
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#include <linux/bpf.h>
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#include <linux/irq_work.h>
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#include <linux/bpf_mem_alloc.h>
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#include <linux/memcontrol.h>
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#include <asm/local.h>
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/* Any context (including NMI) BPF specific memory allocator.
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*
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* Tracing BPF programs can attach to kprobe and fentry. Hence they
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* run in unknown context where calling plain kmalloc() might not be safe.
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*
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* Front-end kmalloc() with per-cpu per-bucket cache of free elements.
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* Refill this cache asynchronously from irq_work.
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*
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* CPU_0 buckets
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* 16 32 64 96 128 196 256 512 1024 2048 4096
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* ...
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* CPU_N buckets
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* 16 32 64 96 128 196 256 512 1024 2048 4096
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*
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* The buckets are prefilled at the start.
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* BPF programs always run with migration disabled.
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* It's safe to allocate from cache of the current cpu with irqs disabled.
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* Free-ing is always done into bucket of the current cpu as well.
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* irq_work trims extra free elements from buckets with kfree
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* and refills them with kmalloc, so global kmalloc logic takes care
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* of freeing objects allocated by one cpu and freed on another.
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*
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* Every allocated objected is padded with extra 8 bytes that contains
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* struct llist_node.
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*/
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#define LLIST_NODE_SZ sizeof(struct llist_node)
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/* similar to kmalloc, but sizeof == 8 bucket is gone */
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static u8 size_index[24] __ro_after_init = {
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3, /* 8 */
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3, /* 16 */
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4, /* 24 */
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4, /* 32 */
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5, /* 40 */
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5, /* 48 */
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5, /* 56 */
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5, /* 64 */
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1, /* 72 */
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1, /* 80 */
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1, /* 88 */
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1, /* 96 */
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6, /* 104 */
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6, /* 112 */
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6, /* 120 */
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6, /* 128 */
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2, /* 136 */
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2, /* 144 */
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2, /* 152 */
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2, /* 160 */
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2, /* 168 */
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2, /* 176 */
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2, /* 184 */
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2 /* 192 */
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};
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static int bpf_mem_cache_idx(size_t size)
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{
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if (!size || size > 4096)
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return -1;
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if (size <= 192)
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return size_index[(size - 1) / 8] - 1;
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return fls(size - 1) - 1;
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}
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#define NUM_CACHES 11
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struct bpf_mem_cache {
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/* per-cpu list of free objects of size 'unit_size'.
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* All accesses are done with interrupts disabled and 'active' counter
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* protection with __llist_add() and __llist_del_first().
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*/
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struct llist_head free_llist;
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local_t active;
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/* Operations on the free_list from unit_alloc/unit_free/bpf_mem_refill
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* are sequenced by per-cpu 'active' counter. But unit_free() cannot
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* fail. When 'active' is busy the unit_free() will add an object to
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* free_llist_extra.
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*/
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struct llist_head free_llist_extra;
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struct irq_work refill_work;
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struct obj_cgroup *objcg;
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int unit_size;
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/* count of objects in free_llist */
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int free_cnt;
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int low_watermark, high_watermark, batch;
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int percpu_size;
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struct rcu_head rcu;
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struct llist_head free_by_rcu;
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struct llist_head waiting_for_gp;
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atomic_t call_rcu_in_progress;
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};
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struct bpf_mem_caches {
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struct bpf_mem_cache cache[NUM_CACHES];
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};
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static struct llist_node notrace *__llist_del_first(struct llist_head *head)
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{
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struct llist_node *entry, *next;
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entry = head->first;
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if (!entry)
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return NULL;
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next = entry->next;
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head->first = next;
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return entry;
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}
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static void *__alloc(struct bpf_mem_cache *c, int node)
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{
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/* Allocate, but don't deplete atomic reserves that typical
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* GFP_ATOMIC would do. irq_work runs on this cpu and kmalloc
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* will allocate from the current numa node which is what we
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* want here.
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*/
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gfp_t flags = GFP_NOWAIT | __GFP_NOWARN | __GFP_ACCOUNT;
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if (c->percpu_size) {
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void **obj = kmalloc_node(c->percpu_size, flags, node);
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void *pptr = __alloc_percpu_gfp(c->unit_size, 8, flags);
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if (!obj || !pptr) {
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free_percpu(pptr);
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kfree(obj);
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return NULL;
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}
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obj[1] = pptr;
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return obj;
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}
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return kmalloc_node(c->unit_size, flags, node);
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}
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static struct mem_cgroup *get_memcg(const struct bpf_mem_cache *c)
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{
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#ifdef CONFIG_MEMCG_KMEM
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if (c->objcg)
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return get_mem_cgroup_from_objcg(c->objcg);
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#endif
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#ifdef CONFIG_MEMCG
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return root_mem_cgroup;
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#else
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return NULL;
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#endif
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}
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/* Mostly runs from irq_work except __init phase. */
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static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
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{
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struct mem_cgroup *memcg = NULL, *old_memcg;
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unsigned long flags;
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void *obj;
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int i;
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memcg = get_memcg(c);
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old_memcg = set_active_memcg(memcg);
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for (i = 0; i < cnt; i++) {
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/*
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* free_by_rcu is only manipulated by irq work refill_work().
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* IRQ works on the same CPU are called sequentially, so it is
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* safe to use __llist_del_first() here. If alloc_bulk() is
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* invoked by the initial prefill, there will be no running
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* refill_work(), so __llist_del_first() is fine as well.
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*
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* In most cases, objects on free_by_rcu are from the same CPU.
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* If some objects come from other CPUs, it doesn't incur any
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* harm because NUMA_NO_NODE means the preference for current
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* numa node and it is not a guarantee.
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*/
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obj = __llist_del_first(&c->free_by_rcu);
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if (!obj) {
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obj = __alloc(c, node);
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if (!obj)
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break;
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}
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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/* In RT irq_work runs in per-cpu kthread, so disable
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* interrupts to avoid preemption and interrupts and
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* reduce the chance of bpf prog executing on this cpu
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* when active counter is busy.
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*/
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local_irq_save(flags);
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/* alloc_bulk runs from irq_work which will not preempt a bpf
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* program that does unit_alloc/unit_free since IRQs are
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* disabled there. There is no race to increment 'active'
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* counter. It protects free_llist from corruption in case NMI
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* bpf prog preempted this loop.
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*/
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WARN_ON_ONCE(local_inc_return(&c->active) != 1);
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__llist_add(obj, &c->free_llist);
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c->free_cnt++;
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local_dec(&c->active);
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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local_irq_restore(flags);
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}
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set_active_memcg(old_memcg);
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mem_cgroup_put(memcg);
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}
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static void free_one(struct bpf_mem_cache *c, void *obj)
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{
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if (c->percpu_size) {
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free_percpu(((void **)obj)[1]);
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kfree(obj);
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return;
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}
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kfree(obj);
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}
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static void __free_rcu(struct rcu_head *head)
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{
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struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
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struct llist_node *llnode = llist_del_all(&c->waiting_for_gp);
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struct llist_node *pos, *t;
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llist_for_each_safe(pos, t, llnode)
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free_one(c, pos);
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atomic_set(&c->call_rcu_in_progress, 0);
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}
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static void __free_rcu_tasks_trace(struct rcu_head *head)
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{
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/* If RCU Tasks Trace grace period implies RCU grace period,
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* there is no need to invoke call_rcu().
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*/
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if (rcu_trace_implies_rcu_gp())
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__free_rcu(head);
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else
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call_rcu(head, __free_rcu);
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}
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static void enque_to_free(struct bpf_mem_cache *c, void *obj)
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{
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struct llist_node *llnode = obj;
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/* bpf_mem_cache is a per-cpu object. Freeing happens in irq_work.
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* Nothing races to add to free_by_rcu list.
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*/
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__llist_add(llnode, &c->free_by_rcu);
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}
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static void do_call_rcu(struct bpf_mem_cache *c)
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{
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struct llist_node *llnode, *t;
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if (atomic_xchg(&c->call_rcu_in_progress, 1))
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return;
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WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
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llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
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/* There is no concurrent __llist_add(waiting_for_gp) access.
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* It doesn't race with llist_del_all either.
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* But there could be two concurrent llist_del_all(waiting_for_gp):
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* from __free_rcu() and from drain_mem_cache().
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*/
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__llist_add(llnode, &c->waiting_for_gp);
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/* Use call_rcu_tasks_trace() to wait for sleepable progs to finish.
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* If RCU Tasks Trace grace period implies RCU grace period, free
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* these elements directly, else use call_rcu() to wait for normal
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* progs to finish and finally do free_one() on each element.
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*/
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call_rcu_tasks_trace(&c->rcu, __free_rcu_tasks_trace);
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}
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static void free_bulk(struct bpf_mem_cache *c)
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{
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struct llist_node *llnode, *t;
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unsigned long flags;
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int cnt;
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do {
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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local_irq_save(flags);
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WARN_ON_ONCE(local_inc_return(&c->active) != 1);
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llnode = __llist_del_first(&c->free_llist);
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if (llnode)
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cnt = --c->free_cnt;
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else
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cnt = 0;
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local_dec(&c->active);
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if (IS_ENABLED(CONFIG_PREEMPT_RT))
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local_irq_restore(flags);
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if (llnode)
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enque_to_free(c, llnode);
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} while (cnt > (c->high_watermark + c->low_watermark) / 2);
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/* and drain free_llist_extra */
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llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra))
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enque_to_free(c, llnode);
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do_call_rcu(c);
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}
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static void bpf_mem_refill(struct irq_work *work)
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{
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struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
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int cnt;
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/* Racy access to free_cnt. It doesn't need to be 100% accurate */
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cnt = c->free_cnt;
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if (cnt < c->low_watermark)
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/* irq_work runs on this cpu and kmalloc will allocate
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* from the current numa node which is what we want here.
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*/
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alloc_bulk(c, c->batch, NUMA_NO_NODE);
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else if (cnt > c->high_watermark)
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free_bulk(c);
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}
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static void notrace irq_work_raise(struct bpf_mem_cache *c)
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{
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irq_work_queue(&c->refill_work);
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}
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/* For typical bpf map case that uses bpf_mem_cache_alloc and single bucket
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* the freelist cache will be elem_size * 64 (or less) on each cpu.
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*
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* For bpf programs that don't have statically known allocation sizes and
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* assuming (low_mark + high_mark) / 2 as an average number of elements per
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* bucket and all buckets are used the total amount of memory in freelists
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* on each cpu will be:
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* 64*16 + 64*32 + 64*64 + 64*96 + 64*128 + 64*196 + 64*256 + 32*512 + 16*1024 + 8*2048 + 4*4096
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* == ~ 116 Kbyte using below heuristic.
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* Initialized, but unused bpf allocator (not bpf map specific one) will
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* consume ~ 11 Kbyte per cpu.
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* Typical case will be between 11K and 116K closer to 11K.
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* bpf progs can and should share bpf_mem_cache when possible.
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*/
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static void prefill_mem_cache(struct bpf_mem_cache *c, int cpu)
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{
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init_irq_work(&c->refill_work, bpf_mem_refill);
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if (c->unit_size <= 256) {
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c->low_watermark = 32;
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c->high_watermark = 96;
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} else {
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/* When page_size == 4k, order-0 cache will have low_mark == 2
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* and high_mark == 6 with batch alloc of 3 individual pages at
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* a time.
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* 8k allocs and above low == 1, high == 3, batch == 1.
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*/
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c->low_watermark = max(32 * 256 / c->unit_size, 1);
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c->high_watermark = max(96 * 256 / c->unit_size, 3);
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}
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c->batch = max((c->high_watermark - c->low_watermark) / 4 * 3, 1);
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/* To avoid consuming memory assume that 1st run of bpf
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* prog won't be doing more than 4 map_update_elem from
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* irq disabled region
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*/
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alloc_bulk(c, c->unit_size <= 256 ? 4 : 1, cpu_to_node(cpu));
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}
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/* When size != 0 bpf_mem_cache for each cpu.
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* This is typical bpf hash map use case when all elements have equal size.
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*
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* When size == 0 allocate 11 bpf_mem_cache-s for each cpu, then rely on
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* kmalloc/kfree. Max allocation size is 4096 in this case.
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* This is bpf_dynptr and bpf_kptr use case.
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*/
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int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size, bool percpu)
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{
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static u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096};
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struct bpf_mem_caches *cc, __percpu *pcc;
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struct bpf_mem_cache *c, __percpu *pc;
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struct obj_cgroup *objcg = NULL;
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int cpu, i, unit_size, percpu_size = 0;
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if (size) {
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pc = __alloc_percpu_gfp(sizeof(*pc), 8, GFP_KERNEL);
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if (!pc)
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return -ENOMEM;
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if (percpu)
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/* room for llist_node and per-cpu pointer */
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percpu_size = LLIST_NODE_SZ + sizeof(void *);
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else
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size += LLIST_NODE_SZ; /* room for llist_node */
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unit_size = size;
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#ifdef CONFIG_MEMCG_KMEM
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objcg = get_obj_cgroup_from_current();
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#endif
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for_each_possible_cpu(cpu) {
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c = per_cpu_ptr(pc, cpu);
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c->unit_size = unit_size;
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c->objcg = objcg;
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c->percpu_size = percpu_size;
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prefill_mem_cache(c, cpu);
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}
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ma->cache = pc;
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return 0;
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}
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/* size == 0 && percpu is an invalid combination */
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if (WARN_ON_ONCE(percpu))
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return -EINVAL;
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pcc = __alloc_percpu_gfp(sizeof(*cc), 8, GFP_KERNEL);
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if (!pcc)
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return -ENOMEM;
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#ifdef CONFIG_MEMCG_KMEM
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objcg = get_obj_cgroup_from_current();
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#endif
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for_each_possible_cpu(cpu) {
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cc = per_cpu_ptr(pcc, cpu);
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for (i = 0; i < NUM_CACHES; i++) {
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c = &cc->cache[i];
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c->unit_size = sizes[i];
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c->objcg = objcg;
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prefill_mem_cache(c, cpu);
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}
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}
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ma->caches = pcc;
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return 0;
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}
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static void drain_mem_cache(struct bpf_mem_cache *c)
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{
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struct llist_node *llnode, *t;
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/* No progs are using this bpf_mem_cache, but htab_map_free() called
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* bpf_mem_cache_free() for all remaining elements and they can be in
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* free_by_rcu or in waiting_for_gp lists, so drain those lists now.
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*
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* Except for waiting_for_gp list, there are no concurrent operations
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* on these lists, so it is safe to use __llist_del_all().
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*/
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llist_for_each_safe(llnode, t, __llist_del_all(&c->free_by_rcu))
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free_one(c, llnode);
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llist_for_each_safe(llnode, t, llist_del_all(&c->waiting_for_gp))
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free_one(c, llnode);
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llist_for_each_safe(llnode, t, __llist_del_all(&c->free_llist))
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free_one(c, llnode);
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llist_for_each_safe(llnode, t, __llist_del_all(&c->free_llist_extra))
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free_one(c, llnode);
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}
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static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
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{
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free_percpu(ma->cache);
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free_percpu(ma->caches);
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ma->cache = NULL;
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ma->caches = NULL;
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}
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|
|
|
static void free_mem_alloc(struct bpf_mem_alloc *ma)
|
|
{
|
|
/* waiting_for_gp lists was drained, but __free_rcu might
|
|
* still execute. Wait for it now before we freeing percpu caches.
|
|
*
|
|
* rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
|
|
* but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
|
|
* to wait for the pending __free_rcu_tasks_trace() and __free_rcu(),
|
|
* so if call_rcu(head, __free_rcu) is skipped due to
|
|
* rcu_trace_implies_rcu_gp(), it will be OK to skip rcu_barrier() by
|
|
* using rcu_trace_implies_rcu_gp() as well.
|
|
*/
|
|
rcu_barrier_tasks_trace();
|
|
if (!rcu_trace_implies_rcu_gp())
|
|
rcu_barrier();
|
|
free_mem_alloc_no_barrier(ma);
|
|
}
|
|
|
|
static void free_mem_alloc_deferred(struct work_struct *work)
|
|
{
|
|
struct bpf_mem_alloc *ma = container_of(work, struct bpf_mem_alloc, work);
|
|
|
|
free_mem_alloc(ma);
|
|
kfree(ma);
|
|
}
|
|
|
|
static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress)
|
|
{
|
|
struct bpf_mem_alloc *copy;
|
|
|
|
if (!rcu_in_progress) {
|
|
/* Fast path. No callbacks are pending, hence no need to do
|
|
* rcu_barrier-s.
|
|
*/
|
|
free_mem_alloc_no_barrier(ma);
|
|
return;
|
|
}
|
|
|
|
copy = kmalloc(sizeof(*ma), GFP_KERNEL);
|
|
if (!copy) {
|
|
/* Slow path with inline barrier-s */
|
|
free_mem_alloc(ma);
|
|
return;
|
|
}
|
|
|
|
/* Defer barriers into worker to let the rest of map memory to be freed */
|
|
copy->cache = ma->cache;
|
|
ma->cache = NULL;
|
|
copy->caches = ma->caches;
|
|
ma->caches = NULL;
|
|
INIT_WORK(©->work, free_mem_alloc_deferred);
|
|
queue_work(system_unbound_wq, ©->work);
|
|
}
|
|
|
|
void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
|
|
{
|
|
struct bpf_mem_caches *cc;
|
|
struct bpf_mem_cache *c;
|
|
int cpu, i, rcu_in_progress;
|
|
|
|
if (ma->cache) {
|
|
rcu_in_progress = 0;
|
|
for_each_possible_cpu(cpu) {
|
|
c = per_cpu_ptr(ma->cache, cpu);
|
|
/*
|
|
* refill_work may be unfinished for PREEMPT_RT kernel
|
|
* in which irq work is invoked in a per-CPU RT thread.
|
|
* It is also possible for kernel with
|
|
* arch_irq_work_has_interrupt() being false and irq
|
|
* work is invoked in timer interrupt. So waiting for
|
|
* the completion of irq work to ease the handling of
|
|
* concurrency.
|
|
*/
|
|
irq_work_sync(&c->refill_work);
|
|
drain_mem_cache(c);
|
|
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
|
|
}
|
|
/* objcg is the same across cpus */
|
|
if (c->objcg)
|
|
obj_cgroup_put(c->objcg);
|
|
destroy_mem_alloc(ma, rcu_in_progress);
|
|
}
|
|
if (ma->caches) {
|
|
rcu_in_progress = 0;
|
|
for_each_possible_cpu(cpu) {
|
|
cc = per_cpu_ptr(ma->caches, cpu);
|
|
for (i = 0; i < NUM_CACHES; i++) {
|
|
c = &cc->cache[i];
|
|
irq_work_sync(&c->refill_work);
|
|
drain_mem_cache(c);
|
|
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
|
|
}
|
|
}
|
|
if (c->objcg)
|
|
obj_cgroup_put(c->objcg);
|
|
destroy_mem_alloc(ma, rcu_in_progress);
|
|
}
|
|
}
|
|
|
|
/* notrace is necessary here and in other functions to make sure
|
|
* bpf programs cannot attach to them and cause llist corruptions.
|
|
*/
|
|
static void notrace *unit_alloc(struct bpf_mem_cache *c)
|
|
{
|
|
struct llist_node *llnode = NULL;
|
|
unsigned long flags;
|
|
int cnt = 0;
|
|
|
|
/* Disable irqs to prevent the following race for majority of prog types:
|
|
* prog_A
|
|
* bpf_mem_alloc
|
|
* preemption or irq -> prog_B
|
|
* bpf_mem_alloc
|
|
*
|
|
* but prog_B could be a perf_event NMI prog.
|
|
* Use per-cpu 'active' counter to order free_list access between
|
|
* unit_alloc/unit_free/bpf_mem_refill.
|
|
*/
|
|
local_irq_save(flags);
|
|
if (local_inc_return(&c->active) == 1) {
|
|
llnode = __llist_del_first(&c->free_llist);
|
|
if (llnode)
|
|
cnt = --c->free_cnt;
|
|
}
|
|
local_dec(&c->active);
|
|
local_irq_restore(flags);
|
|
|
|
WARN_ON(cnt < 0);
|
|
|
|
if (cnt < c->low_watermark)
|
|
irq_work_raise(c);
|
|
return llnode;
|
|
}
|
|
|
|
/* Though 'ptr' object could have been allocated on a different cpu
|
|
* add it to the free_llist of the current cpu.
|
|
* Let kfree() logic deal with it when it's later called from irq_work.
|
|
*/
|
|
static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
|
|
{
|
|
struct llist_node *llnode = ptr - LLIST_NODE_SZ;
|
|
unsigned long flags;
|
|
int cnt = 0;
|
|
|
|
BUILD_BUG_ON(LLIST_NODE_SZ > 8);
|
|
|
|
local_irq_save(flags);
|
|
if (local_inc_return(&c->active) == 1) {
|
|
__llist_add(llnode, &c->free_llist);
|
|
cnt = ++c->free_cnt;
|
|
} else {
|
|
/* unit_free() cannot fail. Therefore add an object to atomic
|
|
* llist. free_bulk() will drain it. Though free_llist_extra is
|
|
* a per-cpu list we have to use atomic llist_add here, since
|
|
* it also can be interrupted by bpf nmi prog that does another
|
|
* unit_free() into the same free_llist_extra.
|
|
*/
|
|
llist_add(llnode, &c->free_llist_extra);
|
|
}
|
|
local_dec(&c->active);
|
|
local_irq_restore(flags);
|
|
|
|
if (cnt > c->high_watermark)
|
|
/* free few objects from current cpu into global kmalloc pool */
|
|
irq_work_raise(c);
|
|
}
|
|
|
|
/* Called from BPF program or from sys_bpf syscall.
|
|
* In both cases migration is disabled.
|
|
*/
|
|
void notrace *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size)
|
|
{
|
|
int idx;
|
|
void *ret;
|
|
|
|
if (!size)
|
|
return ZERO_SIZE_PTR;
|
|
|
|
idx = bpf_mem_cache_idx(size + LLIST_NODE_SZ);
|
|
if (idx < 0)
|
|
return NULL;
|
|
|
|
ret = unit_alloc(this_cpu_ptr(ma->caches)->cache + idx);
|
|
return !ret ? NULL : ret + LLIST_NODE_SZ;
|
|
}
|
|
|
|
void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
|
|
{
|
|
int idx;
|
|
|
|
if (!ptr)
|
|
return;
|
|
|
|
idx = bpf_mem_cache_idx(ksize(ptr - LLIST_NODE_SZ));
|
|
if (idx < 0)
|
|
return;
|
|
|
|
unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
|
|
}
|
|
|
|
void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
|
|
{
|
|
void *ret;
|
|
|
|
ret = unit_alloc(this_cpu_ptr(ma->cache));
|
|
return !ret ? NULL : ret + LLIST_NODE_SZ;
|
|
}
|
|
|
|
void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
|
|
{
|
|
if (!ptr)
|
|
return;
|
|
|
|
unit_free(this_cpu_ptr(ma->cache), ptr);
|
|
}
|