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649 lines
17 KiB
649 lines
17 KiB
// 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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|
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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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|
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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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obj = __alloc(c, node); |
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if (!obj) |
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break; |
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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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struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu); |
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call_rcu(&c->rcu, __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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* Then use call_rcu() to wait for normal progs to finish |
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* 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) |
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{ |
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/* waiting_for_gp lists was drained, but __free_rcu might |
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* still execute. Wait for it now before we freeing percpu caches. |
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*/ |
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rcu_barrier_tasks_trace(); |
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rcu_barrier(); |
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free_mem_alloc_no_barrier(ma); |
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} |
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static void free_mem_alloc_deferred(struct work_struct *work) |
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{ |
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struct bpf_mem_alloc *ma = container_of(work, struct bpf_mem_alloc, work); |
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free_mem_alloc(ma); |
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kfree(ma); |
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} |
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static void destroy_mem_alloc(struct bpf_mem_alloc *ma, int rcu_in_progress) |
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{ |
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struct bpf_mem_alloc *copy; |
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if (!rcu_in_progress) { |
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/* Fast path. No callbacks are pending, hence no need to do |
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* rcu_barrier-s. |
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*/ |
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free_mem_alloc_no_barrier(ma); |
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return; |
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} |
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copy = kmalloc(sizeof(*ma), GFP_KERNEL); |
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if (!copy) { |
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/* Slow path with inline barrier-s */ |
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free_mem_alloc(ma); |
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return; |
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} |
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/* Defer barriers into worker to let the rest of map memory to be freed */ |
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copy->cache = ma->cache; |
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ma->cache = NULL; |
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copy->caches = ma->caches; |
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ma->caches = NULL; |
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INIT_WORK(©->work, free_mem_alloc_deferred); |
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queue_work(system_unbound_wq, ©->work); |
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} |
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void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma) |
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{ |
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struct bpf_mem_caches *cc; |
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struct bpf_mem_cache *c; |
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int cpu, i, rcu_in_progress; |
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if (ma->cache) { |
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rcu_in_progress = 0; |
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for_each_possible_cpu(cpu) { |
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c = per_cpu_ptr(ma->cache, cpu); |
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/* |
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* refill_work may be unfinished for PREEMPT_RT kernel |
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* in which irq work is invoked in a per-CPU RT thread. |
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* It is also possible for kernel with |
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* arch_irq_work_has_interrupt() being false and irq |
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* work is invoked in timer interrupt. So waiting for |
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* the completion of irq work to ease the handling of |
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* concurrency. |
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*/ |
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irq_work_sync(&c->refill_work); |
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drain_mem_cache(c); |
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rcu_in_progress += atomic_read(&c->call_rcu_in_progress); |
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} |
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/* objcg is the same across cpus */ |
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if (c->objcg) |
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obj_cgroup_put(c->objcg); |
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destroy_mem_alloc(ma, rcu_in_progress); |
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} |
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if (ma->caches) { |
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rcu_in_progress = 0; |
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for_each_possible_cpu(cpu) { |
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cc = per_cpu_ptr(ma->caches, cpu); |
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for (i = 0; i < NUM_CACHES; i++) { |
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c = &cc->cache[i]; |
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irq_work_sync(&c->refill_work); |
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drain_mem_cache(c); |
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rcu_in_progress += atomic_read(&c->call_rcu_in_progress); |
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} |
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} |
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if (c->objcg) |
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obj_cgroup_put(c->objcg); |
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destroy_mem_alloc(ma, rcu_in_progress); |
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} |
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} |
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|
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/* notrace is necessary here and in other functions to make sure |
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* bpf programs cannot attach to them and cause llist corruptions. |
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*/ |
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static void notrace *unit_alloc(struct bpf_mem_cache *c) |
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{ |
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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); |
|
}
|
|
|