// SPDX-License-Identifier: GPL-2.0-only
/* bpf/cpumap.c
*
* Copyright (c) 2017 Jesper Dangaard Brouer, Red Hat Inc.
*/
/**
* DOC: cpu map
* The 'cpumap' is primarily used as a backend map for XDP BPF helper
* call bpf_redirect_map() and XDP_REDIRECT action, like 'devmap'.
*
* Unlike devmap which redirects XDP frames out to another NIC device,
* this map type redirects raw XDP frames to another CPU. The remote
* CPU will do SKB-allocation and call the normal network stack.
*/
/*
* This is a scalability and isolation mechanism, that allow
* separating the early driver network XDP layer, from the rest of the
* netstack, and assigning dedicated CPUs for this stage. This
* basically allows for 10G wirespeed pre-filtering via bpf.
*/
#include <linux/bitops.h>
#include <linux/bpf.h>
#include <linux/filter.h>
#include <linux/ptr_ring.h>
#include <net/xdp.h>
#include <net/hotdata.h>
#include <linux/sched.h>
#include <linux/workqueue.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <trace/events/xdp.h>
#include <linux/btf_ids.h>
#include <linux/netdevice.h> /* netif_receive_skb_list */
#include <linux/etherdevice.h> /* eth_type_trans */
/* General idea: XDP packets getting XDP redirected to another CPU,
* will maximum be stored/queued for one driver ->poll() call. It is
* guaranteed that queueing the frame and the flush operation happen on
* same CPU. Thus, cpu_map_flush operation can deduct via this_cpu_ptr()
* which queue in bpf_cpu_map_entry contains packets.
*/
#define CPU_MAP_BULK_SIZE 8 /* 8 == one cacheline on 64-bit archs */
struct bpf_cpu_map_entry;
struct bpf_cpu_map;
struct xdp_bulk_queue {
void *q[CPU_MAP_BULK_SIZE];
struct list_head flush_node;
struct bpf_cpu_map_entry *obj;
unsigned int count;
};
/* Struct for every remote "destination" CPU in map */
struct bpf_cpu_map_entry {
u32 cpu; /* kthread CPU and map index */
int map_id; /* Back reference to map */
/* XDP can run multiple RX-ring queues, need __percpu enqueue store */
struct xdp_bulk_queue __percpu *bulkq;
/* Queue with potential multi-producers, and single-consumer kthread */
struct ptr_ring *queue;
struct task_struct *kthread;
struct bpf_cpumap_val value;
struct bpf_prog *prog;
struct completion kthread_running;
struct rcu_work free_work;
};
struct bpf_cpu_map {
struct bpf_map map;
/* Below members specific for map type */
struct bpf_cpu_map_entry __rcu **cpu_map;
};
static struct bpf_map *cpu_map_alloc(union bpf_attr *attr)
{
u32 value_size = attr->value_size;
struct bpf_cpu_map *cmap;
/* check sanity of attributes */
if (attr->max_entries == 0 || attr->key_size != 4 ||
(value_size != offsetofend(struct bpf_cpumap_val, qsize) &&
value_size != offsetofend(struct bpf_cpumap_val, bpf_prog.fd)) ||
attr->map_flags & ~BPF_F_NUMA_NODE)
return ERR_PTR(-EINVAL);
/* Pre-limit array size based on NR_CPUS, not final CPU check */
if (attr->max_entries > NR_CPUS)
return ERR_PTR(-E2BIG);
cmap = bpf_map_area_alloc(sizeof(*cmap), NUMA_NO_NODE);
if (!cmap)
return ERR_PTR(-ENOMEM);
bpf_map_init_from_attr(&cmap->map, attr);
/* Alloc array for possible remote "destination" CPUs */
cmap->cpu_map = bpf_map_area_alloc(cmap->map.max_entries *
sizeof(struct bpf_cpu_map_entry *),
cmap->map.numa_node);
if (!cmap->cpu_map) {
bpf_map_area_free(cmap);
return ERR_PTR(-ENOMEM);
}
return &cmap->map;
}
static void __cpu_map_ring_cleanup(struct ptr_ring *ring)
{
/* The tear-down procedure should have made sure that queue is
* empty. See __cpu_map_entry_replace() and work-queue
* invoked cpu_map_kthread_stop(). Catch any broken behaviour
* gracefully and warn once.
*/
void *ptr;
while ((ptr = ptr_ring_consume(ring))) {
WARN_ON_ONCE(1);
if (unlikely(__ptr_test_bit(0, &ptr))) {
__ptr_clear_bit(0, &ptr);
kfree_skb(ptr);
continue;
}
xdp_return_frame(ptr);
}
}
static void cpu_map_bpf_prog_run_skb(struct bpf_cpu_map_entry *rcpu,
struct list_head *listp,
struct xdp_cpumap_stats *stats)
{
struct sk_buff *skb, *tmp;
struct xdp_buff xdp;
u32 act;
int err;
list_for_each_entry_safe(skb, tmp, listp, list) {
act = bpf_prog_run_generic_xdp(skb, &xdp, rcpu->prog);
switch (act) {
case XDP_PASS:
break;
case XDP_REDIRECT:
skb_list_del_init(skb);
err = xdp_do_generic_redirect(skb->dev, skb, &xdp,
rcpu->prog);
if (unlikely(err)) {
kfree_skb(skb);
stats->drop++;
} else {
stats->redirect++;
}
return;
default:
bpf_warn_invalid_xdp_action(NULL, rcpu->prog, act);
fallthrough;
case XDP_ABORTED:
trace_xdp_exception(skb->dev, rcpu->prog, act);
fallthrough;
case XDP_DROP:
skb_list_del_init(skb);
kfree_skb(skb);
stats->drop++;
return;
}
}
}
static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
void **frames, int n,
struct xdp_cpumap_stats *stats)
{
struct xdp_rxq_info rxq = {};
struct xdp_buff xdp;
int i, nframes = 0;
xdp_set_return_frame_no_direct();
xdp.rxq = &rxq;
for (i = 0; i < n; i++) {
struct xdp_frame *xdpf = frames[i];
u32 act;
int err;
rxq.dev = xdpf->dev_rx;
rxq.mem = xdpf->mem;
/* TODO: report queue_index to xdp_rxq_info */
xdp_convert_frame_to_buff(xdpf, &xdp);
act = bpf_prog_run_xdp(rcpu->prog, &xdp);
switch (act) {
case XDP_PASS:
err = xdp_update_frame_from_buff(&xdp, xdpf);
if (err < 0) {
xdp_return_frame(xdpf);
stats->drop++;
} else {
frames[nframes++] = xdpf;
stats->pass++;
}
break;
case XDP_REDIRECT:
err = xdp_do_redirect(xdpf->dev_rx, &xdp,
rcpu->prog);
if (unlikely(err)) {
xdp_return_frame(xdpf);
stats->drop++;
} else {
stats->redirect++;
}
break;
default:
bpf_warn_invalid_xdp_action(NULL, rcpu->prog, act);
fallthrough;
case XDP_DROP:
xdp_return_frame(xdpf);
stats->drop++;
break;
}
}
xdp_clear_return_frame_no_direct();
return nframes;
}
#define CPUMAP_BATCH 8
static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
int xdp_n, struct xdp_cpumap_stats *stats,
struct list_head *list)
{
struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
int nframes;
if (!rcpu->prog)
return xdp_n;
rcu_read_lock_bh();
bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
nframes = cpu_map_bpf_prog_run_xdp(rcpu, frames, xdp_n, stats);
if (stats->redirect)
xdp_do_flush();
if (unlikely(!list_empty(list)))
cpu_map_bpf_prog_run_skb(rcpu, list, stats);
bpf_net_ctx_clear(bpf_net_ctx);
rcu_read_unlock_bh(); /* resched point, may call do_softirq() */
return nframes;
}
static int cpu_map_kthread_run(void *data)
{
struct bpf_cpu_map_entry *rcpu = data;
unsigned long last_qs = jiffies;
complete(&rcpu->kthread_running);
set_current_state(TASK_INTERRUPTIBLE);
/* When kthread gives stop order, then rcpu have been disconnected
* from map, thus no new packets can enter. Remaining in-flight
* per CPU stored packets are flushed to this queue. Wait honoring
* kthread_stop signal until queue is empty.
*/
while (!kthread_should_stop() || !__ptr_ring_empty(rcpu->queue)) {
struct xdp_cpumap_stats stats = {}; /* zero stats */
unsigned int kmem_alloc_drops = 0, sched = 0;
gfp_t gfp = __GFP_ZERO | GFP_ATOMIC;
int i, n, m, nframes, xdp_n;
void *frames[CPUMAP_BATCH];
void *skbs[CPUMAP_BATCH];
LIST_HEAD(list);
/* Release CPU reschedule checks */
if (__ptr_ring_empty(rcpu->queue)) {
set_current_state(TASK_INTERRUPTIBLE);
/* Recheck to avoid lost wake-up */
if (__ptr_ring_empty(rcpu->queue)) {
schedule();
sched = 1;
last_qs = jiffies;
} else {
__set_current_state(TASK_RUNNING);
}
} else {
rcu_softirq_qs_periodic(last_qs);
sched = cond_resched();
}
/*
* The bpf_cpu_map_entry is single consumer, with this
* kthread CPU pinned. Lockless access to ptr_ring
* consume side valid as no-resize allowed of queue.
*/
n = __ptr_ring_consume_batched(rcpu->queue, frames,
CPUMAP_BATCH);
for (i = 0, xdp_n = 0; i < n; i++) {
void *f = frames[i];
struct page *page;
if (unlikely(__ptr_test_bit(0, &f))) {
struct sk_buff *skb = f;
__ptr_clear_bit(0, &skb);
list_add_tail(&skb->list, &list);
continue;
}
frames[xdp_n++] = f;
page = virt_to_page(f);
/* Bring struct page memory area to curr CPU. Read by
* build_skb_around via page_is_pfmemalloc(), and when
* freed written by page_frag_free call.
*/
prefetchw(page);
}
/* Support running another XDP prog on this CPU */
nframes = cpu_map_bpf_prog_run(rcpu, frames, xdp_n, &stats, &list);
if (nframes) {
m = kmem_cache_alloc_bulk(net_hotdata.skbuff_cache,
gfp, nframes, skbs);
if (unlikely(m == 0)) {
for (i = 0; i < nframes; i++)
skbs[i] = NULL; /* effect: xdp_return_frame */
kmem_alloc_drops += nframes;
}
}
local_bh_disable();
for (i = 0; i < nframes; i++) {
struct xdp_frame *xdpf = frames[i];
struct sk_buff *skb = skbs[i];
skb = __xdp_build_skb_from_frame(xdpf, skb,
xdpf->dev_rx);
if (!skb) {
xdp_return_frame(xdpf);
continue;
}
list_add_tail(&skb->list, &list);
}
/* Feedback loop via tracepoint.
* NB: keep before recv to allow measuring enqueue/dequeue latency.
*/
trace_xdp_cpumap_kthread(rcpu->map_id, n, kmem_alloc_drops,
sched, &stats);
netif_receive_skb_list(&list);
local_bh_enable(); /* resched point, may call do_softirq() */
}
__set_current_state(TASK_RUNNING);
return 0;
}
static int __cpu_map_load_bpf_program(struct bpf_cpu_map_entry *rcpu,
struct bpf_map *map, int fd)
{
struct bpf_prog *prog;
prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_XDP);
if (IS_ERR(prog))
return PTR_ERR(prog);
if (prog->expected_attach_type != BPF_XDP_CPUMAP ||
!bpf_prog_map_compatible(map, prog)) {
bpf_prog_put(prog);
return -EINVAL;
}
rcpu->value.bpf_prog.id = prog->aux->id;
rcpu->prog = prog;
return 0;
}
static struct bpf_cpu_map_entry *
__cpu_map_entry_alloc(struct bpf_map *map, struct bpf_cpumap_val *value,
u32 cpu)
{
int numa, err, i, fd = value->bpf_prog.fd;
gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
struct bpf_cpu_map_entry *rcpu;
struct xdp_bulk_queue *bq;
/* Have map->numa_node, but choose node of redirect target CPU */
numa = cpu_to_node(cpu);
rcpu = bpf_map_kmalloc_node(map, sizeof(*rcpu), gfp | __GFP_ZERO, numa);
if (!rcpu)
return NULL;
/* Alloc percpu bulkq */
rcpu->bulkq = bpf_map_alloc_percpu(map, sizeof(*rcpu->bulkq),
sizeof(void *), gfp);
if (!rcpu->bulkq)
goto free_rcu;
for_each_possible_cpu(i) {
bq = per_cpu_ptr(rcpu->bulkq, i);
bq->obj = rcpu;
}
/* Alloc queue */
rcpu->queue = bpf_map_kmalloc_node(map, sizeof(*rcpu->queue), gfp,
numa);
if (!rcpu->queue)
goto free_bulkq;
err = ptr_ring_init(rcpu->queue, value->qsize, gfp);
if (err)
goto free_queue;
rcpu->cpu = cpu;
rcpu->map_id = map->id;
rcpu->value.qsize = value->qsize;
if (fd > 0 && __cpu_map_load_bpf_program(rcpu, map, fd))
goto free_ptr_ring;
/* Setup kthread */
init_completion(&rcpu->kthread_running);
rcpu->kthread = kthread_create_on_node(cpu_map_kthread_run, rcpu, numa,
"cpumap/%d/map:%d", cpu,
map->id);
if (IS_ERR(rcpu->kthread))
goto free_prog;
/* Make sure kthread runs on a single CPU */
kthread_bind(rcpu->kthread, cpu);
wake_up_process(rcpu->kthread);
/* Make sure kthread has been running, so kthread_stop() will not
* stop the kthread prematurely and all pending frames or skbs
* will be handled by the kthread before kthread_stop() returns.
*/
wait_for_completion(&rcpu->kthread_running);
return rcpu;
free_prog:
if (rcpu->prog)
bpf_prog_put(rcpu->prog);
free_ptr_ring:
ptr_ring_cleanup(rcpu->queue, NULL);
free_queue:
kfree(rcpu->queue);
free_bulkq:
free_percpu(rcpu->bulkq);
free_rcu:
kfree(rcpu);
return NULL;
}
static void __cpu_map_entry_free(struct work_struct *work)
{
struct bpf_cpu_map_entry *rcpu;
/* This cpu_map_entry have been disconnected from map and one
* RCU grace-period have elapsed. Thus, XDP cannot queue any
* new packets and cannot change/set flush_needed that can
* find this entry.
*/
rcpu = container_of(to_rcu_work(work), struct bpf_cpu_map_entry, free_work);
/* kthread_stop will wake_up_process and wait for it to complete.
* cpu_map_kthread_run() makes sure the pointer ring is empty
* before exiting.
*/
kthread_stop(rcpu->kthread);
if (rcpu->prog)
bpf_prog_put(rcpu->prog);
/* The queue should be empty at this point */
__cpu_map_ring_cleanup(rcpu->queue);
ptr_ring_cleanup(rcpu->queue, NULL);
kfree(rcpu->queue);
free_percpu(rcpu->bulkq);
kfree(rcpu);
}
/* After the xchg of the bpf_cpu_map_entry pointer, we need to make sure the old
* entry is no longer in use before freeing. We use queue_rcu_work() to call
* __cpu_map_entry_free() in a separate workqueue after waiting for an RCU grace
* period. This means that (a) all pending enqueue and flush operations have
* completed (because of the RCU callback), and (b) we are in a workqueue
* context where we can stop the kthread and wait for it to exit before freeing
* everything.
*/
static void __cpu_map_entry_replace(struct bpf_cpu_map *cmap,
u32 key_cpu, struct bpf_cpu_map_entry *rcpu)
{
struct bpf_cpu_map_entry *old_rcpu;
old_rcpu = unrcu_pointer(xchg(&cmap->cpu_map[key_cpu], RCU_INITIALIZER(rcpu)));
if (old_rcpu) {
INIT_RCU_WORK(&old_rcpu->free_work, __cpu_map_entry_free);
queue_rcu_work(system_wq, &old_rcpu->free_work);
}
}
static long cpu_map_delete_elem(struct bpf_map *map, void *key)
{
struct bpf_cpu_map *cmap = container_of(map, struct bpf_cpu_map, map);
u32 key_cpu = *(u32 *)key;
if (key_cpu >= map->max_entries)
return -EINVAL;
/* notice caller map_delete_elem() uses rcu_read_lock() */
__cpu_map_entry_replace(cmap, key_cpu, NULL);
return 0;
}
static long cpu_map_update_elem(struct bpf_map *map, void *key, void *value,
u64 map_flags)
{
struct bpf_cpu_map *cmap = container_of(map, struct bpf_cpu_map, map);
struct bpf_cpumap_val cpumap_value = {};
struct bpf_cpu_map_entry *rcpu;
/* Array index key correspond to CPU number */
u32 key_cpu = *(u32 *)key;
memcpy(&cpumap_value, value, map->value_size);
if (unlikely(map_flags > BPF_EXIST))
return -EINVAL;
if (unlikely(key_cpu >= cmap->map.max_entries))
return -E2BIG;
if (unlikely(map_flags == BPF_NOEXIST))
return -EEXIST;
if (unlikely(cpumap_value.qsize > 16384)) /* sanity limit on qsize */
return -EOVERFLOW;
/* Make sure CPU is a valid possible cpu */
if (key_cpu >= nr_cpumask_bits || !cpu_possible(key_cpu))
return -ENODEV;
if (cpumap_value.qsize == 0) {
rcpu = NULL; /* Same as deleting */
} else {
/* Updating qsize cause re-allocation of bpf_cpu_map_entry */
rcpu = __cpu_map_entry_alloc(map, &cpumap_value, key_cpu);
if (!rcpu)
return -ENOMEM;
}
rcu_read_lock();
__cpu_map_entry_replace(cmap, key_cpu, rcpu);
rcu_read_unlock();
return 0;
}
static void cpu_map_free(struct bpf_map *map)
{
struct bpf_cpu_map *cmap = container_of(map, struct bpf_cpu_map, map);
u32 i;
/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
* so the bpf programs (can be more than one that used this map) were
* disconnected from events. Wait for outstanding critical sections in
* these programs to complete. synchronize_rcu() below not only
* guarantees no further "XDP/bpf-side" reads against
* bpf_cpu_map->cpu_map, but also ensure pending flush operations
* (if any) are completed.
*/
synchronize_rcu();
/* The only possible user of bpf_cpu_map_entry is
* cpu_map_kthread_run().
*/
for (i = 0; i < cmap->map.max_entries; i++) {
struct bpf_cpu_map_entry *rcpu;
rcpu = rcu_dereference_raw(cmap->cpu_map[i]);
if (!rcpu)
continue;
/* Stop kthread and cleanup entry directly */
__cpu_map_entry_free(&rcpu->free_work.work);
}
bpf_map_area_free(cmap->cpu_map);
bpf_map_area_free(cmap);
}
/* Elements are kept alive by RCU; either by rcu_read_lock() (from syscall) or
* by local_bh_disable() (from XDP calls inside NAPI). The
* rcu_read_lock_bh_held() below makes lockdep accept both.
*/
static void *__cpu_map_lookup_elem(struct bpf_map *map, u32 key)
{
struct bpf_cpu_map *cmap = container_of(map, struct bpf_cpu_map, map);
struct bpf_cpu_map_entry *rcpu;
if (key >= map->max_entries)
return NULL;
rcpu = rcu_dereference_check(cmap->cpu_map[key],
rcu_read_lock_bh_held());
return rcpu;
}
static void *cpu_map_lookup_elem(struct bpf_map *map, void *key)
{
struct bpf_cpu_map_entry *rcpu =
__cpu_map_lookup_elem(map, *(u32 *)key);
return rcpu ? &rcpu->value : NULL;
}
static int cpu_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
{
struct bpf_cpu_map *cmap = container_of(map, struct bpf_cpu_map, map);
u32 index = key ? *(u32 *)key : U32_MAX;
u32 *next = next_key;
if (index >= cmap->map.max_entries) {
*next = 0;
return 0;
}
if (index == cmap->map.max_entries - 1)
return -ENOENT;
*next = index + 1;
return 0;
}
static long cpu_map_redirect(struct bpf_map *map, u64 index, u64 flags)
{
return __bpf_xdp_redirect_map(map, index, flags, 0,
__cpu_map_lookup_elem);
}
static u64 cpu_map_mem_usage(const struct bpf_map *map)
{
u64 usage = sizeof(struct bpf_cpu_map);
/* Currently the dynamically allocated elements are not counted */
usage += (u64)map->max_entries * sizeof(struct bpf_cpu_map_entry *);
return usage;
}
BTF_ID_LIST_SINGLE(cpu_map_btf_ids, struct, bpf_cpu_map)
const struct bpf_map_ops cpu_map_ops = {
.map_meta_equal = bpf_map_meta_equal,
.map_alloc = cpu_map_alloc,
.map_free = cpu_map_free,
.map_delete_elem = cpu_map_delete_elem,
.map_update_elem = cpu_map_update_elem,
.map_lookup_elem = cpu_map_lookup_elem,
.map_get_next_key = cpu_map_get_next_key,
.map_check_btf = map_check_no_btf,
.map_mem_usage = cpu_map_mem_usage,
.map_btf_id = &cpu_map_btf_ids[0],
.map_redirect = cpu_map_redirect,
};
static void bq_flush_to_queue(struct xdp_bulk_queue *bq)
{
struct bpf_cpu_map_entry *rcpu = bq->obj;
unsigned int processed = 0, drops = 0;
const int to_cpu = rcpu->cpu;
struct ptr_ring *q;
int i;
if (unlikely(!bq->count))
return;
q = rcpu->queue;
spin_lock(&q->producer_lock);
for (i = 0; i < bq->count; i++) {
struct xdp_frame *xdpf = bq->q[i];
int err;
err = __ptr_ring_produce(q, xdpf);
if (err) {
drops++;
xdp_return_frame_rx_napi(xdpf);
}
processed++;
}
bq->count = 0;
spin_unlock(&q->producer_lock);
__list_del_clearprev(&bq->flush_node);
/* Feedback loop via tracepoints */
trace_xdp_cpumap_enqueue(rcpu->map_id, processed, drops, to_cpu);
}
/* Runs under RCU-read-side, plus in softirq under NAPI protection.
* Thus, safe percpu variable access.
*/
static void bq_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_frame *xdpf)
{
struct xdp_bulk_queue *bq = this_cpu_ptr(rcpu->bulkq);
if (unlikely(bq->count == CPU_MAP_BULK_SIZE))
bq_flush_to_queue(bq);
/* Notice, xdp_buff/page MUST be queued here, long enough for
* driver to code invoking us to finished, due to driver
* (e.g. ixgbe) recycle tricks based on page-refcnt.
*
* Thus, incoming xdp_frame is always queued here (else we race
* with another CPU on page-refcnt and remaining driver code).
* Queue time is very short, as driver will invoke flush
* operation, when completing napi->poll call.
*/
bq->q[bq->count++] = xdpf;
if (!bq->flush_node.prev) {
struct list_head *flush_list = bpf_net_ctx_get_cpu_map_flush_list();
list_add(&bq->flush_node, flush_list);
}
}
int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_frame *xdpf,
struct net_device *dev_rx)
{
/* Info needed when constructing SKB on remote CPU */
xdpf->dev_rx = dev_rx;
bq_enqueue(rcpu, xdpf);
return 0;
}
int cpu_map_generic_redirect(struct bpf_cpu_map_entry *rcpu,
struct sk_buff *skb)
{
int ret;
__skb_pull(skb, skb->mac_len);
skb_set_redirected(skb, false);
__ptr_set_bit(0, &skb);
ret = ptr_ring_produce(rcpu->queue, skb);
if (ret < 0)
goto trace;
wake_up_process(rcpu->kthread);
trace:
trace_xdp_cpumap_enqueue(rcpu->map_id, !ret, !!ret, rcpu->cpu);
return ret;
}
void __cpu_map_flush(struct list_head *flush_list)
{
struct xdp_bulk_queue *bq, *tmp;
list_for_each_entry_safe(bq, tmp, flush_list, flush_node) {
bq_flush_to_queue(bq);
/* If already running, costs spin_lock_irqsave + smb_mb */
wake_up_process(bq->obj->kthread);
}
}
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