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bpf: Introduce bpf_mem_free_rcu() similar to kfree_rcu(). 

Introduce bpf_mem_[cache_]free_rcu() similar to kfree_rcu().
Unlike bpf_mem_[cache_]free() that links objects for immediate reuse into
per-cpu free list the _rcu() flavor waits for RCU grace period and then moves
objects into free_by_rcu_ttrace list where they are waiting for RCU
task trace grace period to be freed into slab.

The life cycle of objects:
alloc: dequeue free_llist
free: enqeueu free_llist
free_rcu: enqueue free_by_rcu -> waiting_for_gp
free_llist above high watermark -> free_by_rcu_ttrace
after RCU GP waiting_for_gp -> free_by_rcu_ttrace
free_by_rcu_ttrace -> waiting_for_gp_ttrace -> slab

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/bpf/20230706033447.54696-13-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2023-07-05 20:34:45 -07:00 committed by Daniel Borkmann
parent f76faa65c9
commit 5af6807bdb
2 changed files with 128 additions and 3 deletions
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2
include/linux/bpf_mem_alloc.h
View File

@ -27,10 +27,12 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma);
/* kmalloc/kfree equivalent: */
void *bpf_mem_alloc(struct bpf_mem_alloc *ma, size_t size);
void bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr);
void bpf_mem_free_rcu(struct bpf_mem_alloc *ma, void *ptr);
/* kmem_cache_alloc/free equivalent: */
void *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma);
void bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr);
void bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr);
void bpf_mem_cache_raw_free(void *ptr);
void *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags);

129
kernel/bpf/memalloc.c
View File

@ -101,6 +101,15 @@ struct bpf_mem_cache {
bool draining;
struct bpf_mem_cache *tgt;
/* list of objects to be freed after RCU GP */
struct llist_head free_by_rcu;
struct llist_node *free_by_rcu_tail;
struct llist_head waiting_for_gp;
struct llist_node *waiting_for_gp_tail;
struct rcu_head rcu;
atomic_t call_rcu_in_progress;
struct llist_head free_llist_extra_rcu;
/* list of objects to be freed after RCU tasks trace GP */
struct llist_head free_by_rcu_ttrace;
struct llist_head waiting_for_gp_ttrace;
@ -346,6 +355,69 @@ static void free_bulk(struct bpf_mem_cache *c)
do_call_rcu_ttrace(tgt);
}
static void __free_by_rcu(struct rcu_head *head)
{
struct bpf_mem_cache *c = container_of(head, struct bpf_mem_cache, rcu);
struct bpf_mem_cache *tgt = c->tgt;
struct llist_node *llnode;
llnode = llist_del_all(&c->waiting_for_gp);
if (!llnode)
goto out;
llist_add_batch(llnode, c->waiting_for_gp_tail, &tgt->free_by_rcu_ttrace);
/* Objects went through regular RCU GP. Send them to RCU tasks trace */
do_call_rcu_ttrace(tgt);
out:
atomic_set(&c->call_rcu_in_progress, 0);
}
static void check_free_by_rcu(struct bpf_mem_cache *c)
{
struct llist_node *llnode, *t;
unsigned long flags;
/* drain free_llist_extra_rcu */
if (unlikely(!llist_empty(&c->free_llist_extra_rcu))) {
inc_active(c, &flags);
llist_for_each_safe(llnode, t, llist_del_all(&c->free_llist_extra_rcu))
if (__llist_add(llnode, &c->free_by_rcu))
c->free_by_rcu_tail = llnode;
dec_active(c, flags);
}
if (llist_empty(&c->free_by_rcu))
return;
if (atomic_xchg(&c->call_rcu_in_progress, 1)) {
/*
* Instead of kmalloc-ing new rcu_head and triggering 10k
* call_rcu() to hit rcutree.qhimark and force RCU to notice
* the overload just ask RCU to hurry up. There could be many
* objects in free_by_rcu list.
* This hint reduces memory consumption for an artificial
* benchmark from 2 Gbyte to 150 Mbyte.
*/
rcu_request_urgent_qs_task(current);
return;
}
WARN_ON_ONCE(!llist_empty(&c->waiting_for_gp));
inc_active(c, &flags);
WRITE_ONCE(c->waiting_for_gp.first, __llist_del_all(&c->free_by_rcu));
c->waiting_for_gp_tail = c->free_by_rcu_tail;
dec_active(c, flags);
if (unlikely(READ_ONCE(c->draining))) {
free_all(llist_del_all(&c->waiting_for_gp), !!c->percpu_size);
atomic_set(&c->call_rcu_in_progress, 0);
} else {
call_rcu_hurry(&c->rcu, __free_by_rcu);
}
}
static void bpf_mem_refill(struct irq_work *work)
{
struct bpf_mem_cache *c = container_of(work, struct bpf_mem_cache, refill_work);
@ -360,6 +432,8 @@ static void bpf_mem_refill(struct irq_work *work)
alloc_bulk(c, c->batch, NUMA_NO_NODE);
else if (cnt > c->high_watermark)
free_bulk(c);
check_free_by_rcu(c);
}
static void notrace irq_work_raise(struct bpf_mem_cache *c)
@ -488,6 +562,9 @@ static void drain_mem_cache(struct bpf_mem_cache *c)
free_all(llist_del_all(&c->waiting_for_gp_ttrace), percpu);
free_all(__llist_del_all(&c->free_llist), percpu);
free_all(__llist_del_all(&c->free_llist_extra), percpu);
free_all(__llist_del_all(&c->free_by_rcu), percpu);
free_all(__llist_del_all(&c->free_llist_extra_rcu), percpu);
free_all(llist_del_all(&c->waiting_for_gp), percpu);
}
static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
@ -500,8 +577,8 @@ static void free_mem_alloc_no_barrier(struct bpf_mem_alloc *ma)
static void free_mem_alloc(struct bpf_mem_alloc *ma)
{
/* waiting_for_gp_ttrace lists was drained, but __free_rcu might
* still execute. Wait for it now before we freeing percpu caches.
/* waiting_for_gp[_ttrace] lists were drained, but RCU callbacks
* might still execute. Wait for them.
*
* rcu_barrier_tasks_trace() doesn't imply synchronize_rcu_tasks_trace(),
* but rcu_barrier_tasks_trace() and rcu_barrier() below are only used
@ -510,7 +587,8 @@ static void free_mem_alloc(struct bpf_mem_alloc *ma)
* 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();
rcu_barrier(); /* wait for __free_by_rcu */
rcu_barrier_tasks_trace(); /* wait for __free_rcu */
if (!rcu_trace_implies_rcu_gp())
rcu_barrier();
free_mem_alloc_no_barrier(ma);
@ -563,6 +641,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
irq_work_sync(&c->refill_work);
drain_mem_cache(c);
rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
/* objcg is the same across cpus */
if (c->objcg)
@ -579,6 +658,7 @@ void bpf_mem_alloc_destroy(struct bpf_mem_alloc *ma)
irq_work_sync(&c->refill_work);
drain_mem_cache(c);
rcu_in_progress += atomic_read(&c->call_rcu_ttrace_in_progress);
rcu_in_progress += atomic_read(&c->call_rcu_in_progress);
}
}
if (c->objcg)
@ -663,6 +743,27 @@ static void notrace unit_free(struct bpf_mem_cache *c, void *ptr)
irq_work_raise(c);
}
static void notrace unit_free_rcu(struct bpf_mem_cache *c, void *ptr)
{
struct llist_node *llnode = ptr - LLIST_NODE_SZ;
unsigned long flags;
c->tgt = *(struct bpf_mem_cache **)llnode;
local_irq_save(flags);
if (local_inc_return(&c->active) == 1) {
if (__llist_add(llnode, &c->free_by_rcu))
c->free_by_rcu_tail = llnode;
} else {
llist_add(llnode, &c->free_llist_extra_rcu);
}
local_dec(&c->active);
local_irq_restore(flags);
if (!atomic_read(&c->call_rcu_in_progress))
irq_work_raise(c);
}
/* Called from BPF program or from sys_bpf syscall.
* In both cases migration is disabled.
*/
@ -696,6 +797,20 @@ void notrace bpf_mem_free(struct bpf_mem_alloc *ma, void *ptr)
unit_free(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}
void notrace bpf_mem_free_rcu(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_rcu(this_cpu_ptr(ma->caches)->cache + idx, ptr);
}
void notrace *bpf_mem_cache_alloc(struct bpf_mem_alloc *ma)
{
void *ret;
@ -712,6 +827,14 @@ void notrace bpf_mem_cache_free(struct bpf_mem_alloc *ma, void *ptr)
unit_free(this_cpu_ptr(ma->cache), ptr);
}
void notrace bpf_mem_cache_free_rcu(struct bpf_mem_alloc *ma, void *ptr)
{
if (!ptr)
return;
unit_free_rcu(this_cpu_ptr(ma->cache), ptr);
}
/* Directly does a kfree() without putting 'ptr' back to the free_llist
* for reuse and without waiting for a rcu_tasks_trace gp.
* The caller must first go through the rcu_tasks_trace gp for 'ptr'