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linux/io_uring/io-wq.c
Uday Shankar 13918315c5 io-wq: backoff when retrying worker creation 
When io_uring submission goes async for the first time on a given task,
we'll try to create a worker thread to handle the submission. Creating
this worker thread can fail due to various transient conditions, such as
an outstanding signal in the forking thread, so we have retry logic with
a limit of 3 retries. However, this retry logic appears to be too
aggressive/fast - we've observed a thread blowing through the retry
limit while having the same outstanding signal the whole time. Here's an
excerpt of some tracing that demonstrates the issue:

First, signal 26 is generated for the process. It ends up getting routed
to thread 92942.

 0)   cbd-92284    /* signal_generate: sig=26 errno=0 code=-2 comm=psblkdASD pid=92934 grp=1 res=0 */

This causes create_io_thread in the signalled thread to fail with
ERESTARTNOINTR, and thus a retry is queued.

13) task_th-92942  /* io_uring_queue_async_work: ring 000000007325c9ae, request 0000000080c96d8e, user_data 0x0, opcode URING_CMD, flags 0x8240001, normal queue, work 000000006e96dd3f */
13) task_th-92942  io_wq_enqueue() {
13) task_th-92942    _raw_spin_lock();
13) task_th-92942    io_wq_activate_free_worker();
13) task_th-92942    _raw_spin_lock();
13) task_th-92942    create_io_worker() {
13) task_th-92942      __kmalloc_cache_noprof();
13) task_th-92942      __init_swait_queue_head();
13) task_th-92942      kprobe_ftrace_handler() {
13) task_th-92942        get_kprobe();
13) task_th-92942        aggr_pre_handler() {
13) task_th-92942          pre_handler_kretprobe();
13) task_th-92942          /* create_enter: (create_io_thread+0x0/0x50) fn=0xffffffff8172c0e0 arg=0xffff888996bb69c0 node=-1 */
13) task_th-92942        } /* aggr_pre_handler */
...
13) task_th-92942        } /* copy_process */
13) task_th-92942      } /* create_io_thread */
13) task_th-92942      kretprobe_rethook_handler() {
13) task_th-92942        /* create_exit: (create_io_worker+0x8a/0x1a0 <- create_io_thread) arg1=0xfffffffffffffdff */
13) task_th-92942      } /* kretprobe_rethook_handler */
13) task_th-92942    queue_work_on() {
...

The CPU is then handed to a kworker to process the queued retry:

------------------------------------------
 13) task_th-92942  => kworker-54154
------------------------------------------
13) kworker-54154  io_workqueue_create() {
13) kworker-54154    io_queue_worker_create() {
13) kworker-54154      task_work_add() {
13) kworker-54154        wake_up_state() {
13) kworker-54154          try_to_wake_up() {
13) kworker-54154            _raw_spin_lock_irqsave();
13) kworker-54154            _raw_spin_unlock_irqrestore();
13) kworker-54154          } /* try_to_wake_up */
13) kworker-54154        } /* wake_up_state */
13) kworker-54154        kick_process();
13) kworker-54154      } /* task_work_add */
13) kworker-54154    } /* io_queue_worker_create */
13) kworker-54154  } /* io_workqueue_create */

And then we immediately switch back to the original task to try creating
a worker again. This fails, because the original task still hasn't
handled its signal.

-----------------------------------------
 13) kworker-54154  => task_th-92942
------------------------------------------
13) task_th-92942  create_worker_cont() {
13) task_th-92942    kprobe_ftrace_handler() {
13) task_th-92942      get_kprobe();
13) task_th-92942      aggr_pre_handler() {
13) task_th-92942        pre_handler_kretprobe();
13) task_th-92942        /* create_enter: (create_io_thread+0x0/0x50) fn=0xffffffff8172c0e0 arg=0xffff888996bb69c0 node=-1 */
13) task_th-92942      } /* aggr_pre_handler */
13) task_th-92942    } /* kprobe_ftrace_handler */
13) task_th-92942    create_io_thread() {
13) task_th-92942      copy_process() {
13) task_th-92942        task_active_pid_ns();
13) task_th-92942        _raw_spin_lock_irq();
13) task_th-92942        recalc_sigpending();
13) task_th-92942        _raw_spin_lock_irq();
13) task_th-92942      } /* copy_process */
13) task_th-92942    } /* create_io_thread */
13) task_th-92942    kretprobe_rethook_handler() {
13) task_th-92942      /* create_exit: (create_worker_cont+0x35/0x1b0 <- create_io_thread) arg1=0xfffffffffffffdff */
13) task_th-92942    } /* kretprobe_rethook_handler */
13) task_th-92942    io_worker_release();
13) task_th-92942    queue_work_on() {
13) task_th-92942      clear_pending_if_disabled();
13) task_th-92942      __queue_work() {
13) task_th-92942      } /* __queue_work */
13) task_th-92942    } /* queue_work_on */
13) task_th-92942  } /* create_worker_cont */

The pattern repeats another couple times until we blow through the retry
counter, at which point we give up. All outstanding work is canceled,
and the io_uring command which triggered all this is failed with
ECANCELED:

13) task_th-92942  io_acct_cancel_pending_work() {
...
13) task_th-92942  /* io_uring_complete: ring 000000007325c9ae, req 0000000080c96d8e, user_data 0x0, result -125, cflags 0x0 extra1 0 extra2 0  */

Finally, the task gets around to processing its outstanding signal 26,
but it's too late.

13) task_th-92942  /* signal_deliver: sig=26 errno=0 code=-2 sa_handler=59566a0 sa_flags=14000000 */

Try to address this issue by adding a small scaling delay when retrying
worker creation. This should give the forking thread time to handle its
signal in the above case. This isn't a particularly satisfying solution,
as sufficiently paradoxical scheduling would still have us hitting the
same issue, and I'm open to suggestions for something better. But this
is likely to prevent this (already rare) issue from hitting in practice.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Link: https://lore.kernel.org/r/20250208-wq_retry-v2-1-4f6f5041d303@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2025-02-14 15:34:28 -07:00

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// SPDX-License-Identifier: GPL-2.0
/*
* Basic worker thread pool for io_uring
*
* Copyright (C) 2019 Jens Axboe
*
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/sched/signal.h>
#include <linux/percpu.h>
#include <linux/slab.h>
#include <linux/rculist_nulls.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/task_work.h>
#include <linux/audit.h>
#include <linux/mmu_context.h>
#include <uapi/linux/io_uring.h>
#include "io-wq.h"
#include "slist.h"
#include "io_uring.h"
#define WORKER_IDLE_TIMEOUT (5 * HZ)
#define WORKER_INIT_LIMIT 3
enum {
IO_WORKER_F_UP = 0, /* up and active */
IO_WORKER_F_RUNNING = 1, /* account as running */
IO_WORKER_F_FREE = 2, /* worker on free list */
IO_WORKER_F_BOUND = 3, /* is doing bounded work */
};
enum {
IO_WQ_BIT_EXIT = 0, /* wq exiting */
};
enum {
IO_ACCT_STALLED_BIT = 0, /* stalled on hash */
};
/*
* One for each thread in a wq pool
*/
struct io_worker {
refcount_t ref;
int create_index;
unsigned long flags;
struct hlist_nulls_node nulls_node;
struct list_head all_list;
struct task_struct *task;
struct io_wq *wq;
struct io_wq_work *cur_work;
raw_spinlock_t lock;
struct completion ref_done;
unsigned long create_state;
struct callback_head create_work;
int init_retries;
union {
struct rcu_head rcu;
struct delayed_work work;
};
};
#if BITS_PER_LONG == 64
#define IO_WQ_HASH_ORDER 6
#else
#define IO_WQ_HASH_ORDER 5
#endif
#define IO_WQ_NR_HASH_BUCKETS (1u << IO_WQ_HASH_ORDER)
struct io_wq_acct {
unsigned nr_workers;
unsigned max_workers;
int index;
atomic_t nr_running;
raw_spinlock_t lock;
struct io_wq_work_list work_list;
unsigned long flags;
};
enum {
IO_WQ_ACCT_BOUND,
IO_WQ_ACCT_UNBOUND,
IO_WQ_ACCT_NR,
};
/*
* Per io_wq state
*/
struct io_wq {
unsigned long state;
free_work_fn *free_work;
io_wq_work_fn *do_work;
struct io_wq_hash *hash;
atomic_t worker_refs;
struct completion worker_done;
struct hlist_node cpuhp_node;
struct task_struct *task;
struct io_wq_acct acct[IO_WQ_ACCT_NR];
/* lock protects access to elements below */
raw_spinlock_t lock;
struct hlist_nulls_head free_list;
struct list_head all_list;
struct wait_queue_entry wait;
struct io_wq_work *hash_tail[IO_WQ_NR_HASH_BUCKETS];
cpumask_var_t cpu_mask;
};
static enum cpuhp_state io_wq_online;
struct io_cb_cancel_data {
work_cancel_fn *fn;
void *data;
int nr_running;
int nr_pending;
bool cancel_all;
};
static bool create_io_worker(struct io_wq *wq, int index);
static void io_wq_dec_running(struct io_worker *worker);
static bool io_acct_cancel_pending_work(struct io_wq *wq,
struct io_wq_acct *acct,
struct io_cb_cancel_data *match);
static void create_worker_cb(struct callback_head *cb);
static void io_wq_cancel_tw_create(struct io_wq *wq);
static bool io_worker_get(struct io_worker *worker)
{
return refcount_inc_not_zero(&worker->ref);
}
static void io_worker_release(struct io_worker *worker)
{
if (refcount_dec_and_test(&worker->ref))
complete(&worker->ref_done);
}
static inline struct io_wq_acct *io_get_acct(struct io_wq *wq, bool bound)
{
return &wq->acct[bound ? IO_WQ_ACCT_BOUND : IO_WQ_ACCT_UNBOUND];
}
static inline struct io_wq_acct *io_work_get_acct(struct io_wq *wq,
struct io_wq_work *work)
{
return io_get_acct(wq, !(atomic_read(&work->flags) & IO_WQ_WORK_UNBOUND));
}
static inline struct io_wq_acct *io_wq_get_acct(struct io_worker *worker)
{
return io_get_acct(worker->wq, test_bit(IO_WORKER_F_BOUND, &worker->flags));
}
static void io_worker_ref_put(struct io_wq *wq)
{
if (atomic_dec_and_test(&wq->worker_refs))
complete(&wq->worker_done);
}
bool io_wq_worker_stopped(void)
{
struct io_worker *worker = current->worker_private;
if (WARN_ON_ONCE(!io_wq_current_is_worker()))
return true;
return test_bit(IO_WQ_BIT_EXIT, &worker->wq->state);
}
static void io_worker_cancel_cb(struct io_worker *worker)
{
struct io_wq_acct *acct = io_wq_get_acct(worker);
struct io_wq *wq = worker->wq;
atomic_dec(&acct->nr_running);
raw_spin_lock(&wq->lock);
acct->nr_workers--;
raw_spin_unlock(&wq->lock);
io_worker_ref_put(wq);
clear_bit_unlock(0, &worker->create_state);
io_worker_release(worker);
}
static bool io_task_worker_match(struct callback_head *cb, void *data)
{
struct io_worker *worker;
if (cb->func != create_worker_cb)
return false;
worker = container_of(cb, struct io_worker, create_work);
return worker == data;
}
static void io_worker_exit(struct io_worker *worker)
{
struct io_wq *wq = worker->wq;
while (1) {
struct callback_head *cb = task_work_cancel_match(wq->task,
io_task_worker_match, worker);
if (!cb)
break;
io_worker_cancel_cb(worker);
}
io_worker_release(worker);
wait_for_completion(&worker->ref_done);
raw_spin_lock(&wq->lock);
if (test_bit(IO_WORKER_F_FREE, &worker->flags))
hlist_nulls_del_rcu(&worker->nulls_node);
list_del_rcu(&worker->all_list);
raw_spin_unlock(&wq->lock);
io_wq_dec_running(worker);
/*
* this worker is a goner, clear ->worker_private to avoid any
* inc/dec running calls that could happen as part of exit from
* touching 'worker'.
*/
current->worker_private = NULL;
kfree_rcu(worker, rcu);
io_worker_ref_put(wq);
do_exit(0);
}
static inline bool __io_acct_run_queue(struct io_wq_acct *acct)
{
return !test_bit(IO_ACCT_STALLED_BIT, &acct->flags) &&
!wq_list_empty(&acct->work_list);
}
/*
* If there's work to do, returns true with acct->lock acquired. If not,
* returns false with no lock held.
*/
static inline bool io_acct_run_queue(struct io_wq_acct *acct)
__acquires(&acct->lock)
{
raw_spin_lock(&acct->lock);
if (__io_acct_run_queue(acct))
return true;
raw_spin_unlock(&acct->lock);
return false;
}
/*
* Check head of free list for an available worker. If one isn't available,
* caller must create one.
*/
static bool io_wq_activate_free_worker(struct io_wq *wq,
struct io_wq_acct *acct)
__must_hold(RCU)
{
struct hlist_nulls_node *n;
struct io_worker *worker;
/*
* Iterate free_list and see if we can find an idle worker to
* activate. If a given worker is on the free_list but in the process
* of exiting, keep trying.
*/
hlist_nulls_for_each_entry_rcu(worker, n, &wq->free_list, nulls_node) {
if (!io_worker_get(worker))
continue;
if (io_wq_get_acct(worker) != acct) {
io_worker_release(worker);
continue;
}
/*
* If the worker is already running, it's either already
* starting work or finishing work. In either case, if it does
* to go sleep, we'll kick off a new task for this work anyway.
*/
wake_up_process(worker->task);
io_worker_release(worker);
return true;
}
return false;
}
/*
* We need a worker. If we find a free one, we're good. If not, and we're
* below the max number of workers, create one.
*/
static bool io_wq_create_worker(struct io_wq *wq, struct io_wq_acct *acct)
{
/*
* Most likely an attempt to queue unbounded work on an io_wq that
* wasn't setup with any unbounded workers.
*/
if (unlikely(!acct->max_workers))
pr_warn_once("io-wq is not configured for unbound workers");
raw_spin_lock(&wq->lock);
if (acct->nr_workers >= acct->max_workers) {
raw_spin_unlock(&wq->lock);
return true;
}
acct->nr_workers++;
raw_spin_unlock(&wq->lock);
atomic_inc(&acct->nr_running);
atomic_inc(&wq->worker_refs);
return create_io_worker(wq, acct->index);
}
static void io_wq_inc_running(struct io_worker *worker)
{
struct io_wq_acct *acct = io_wq_get_acct(worker);
atomic_inc(&acct->nr_running);
}
static void create_worker_cb(struct callback_head *cb)
{
struct io_worker *worker;
struct io_wq *wq;
struct io_wq_acct *acct;
bool do_create = false;
worker = container_of(cb, struct io_worker, create_work);
wq = worker->wq;
acct = &wq->acct[worker->create_index];
raw_spin_lock(&wq->lock);
if (acct->nr_workers < acct->max_workers) {
acct->nr_workers++;
do_create = true;
}
raw_spin_unlock(&wq->lock);
if (do_create) {
create_io_worker(wq, worker->create_index);
} else {
atomic_dec(&acct->nr_running);
io_worker_ref_put(wq);
}
clear_bit_unlock(0, &worker->create_state);
io_worker_release(worker);
}
static bool io_queue_worker_create(struct io_worker *worker,
struct io_wq_acct *acct,
task_work_func_t func)
{
struct io_wq *wq = worker->wq;
/* raced with exit, just ignore create call */
if (test_bit(IO_WQ_BIT_EXIT, &wq->state))
goto fail;
if (!io_worker_get(worker))
goto fail;
/*
* create_state manages ownership of create_work/index. We should
* only need one entry per worker, as the worker going to sleep
* will trigger the condition, and waking will clear it once it
* runs the task_work.
*/
if (test_bit(0, &worker->create_state) ||
test_and_set_bit_lock(0, &worker->create_state))
goto fail_release;
atomic_inc(&wq->worker_refs);
init_task_work(&worker->create_work, func);
worker->create_index = acct->index;
if (!task_work_add(wq->task, &worker->create_work, TWA_SIGNAL)) {
/*
* EXIT may have been set after checking it above, check after
* adding the task_work and remove any creation item if it is
* now set. wq exit does that too, but we can have added this
* work item after we canceled in io_wq_exit_workers().
*/
if (test_bit(IO_WQ_BIT_EXIT, &wq->state))
io_wq_cancel_tw_create(wq);
io_worker_ref_put(wq);
return true;
}
io_worker_ref_put(wq);
clear_bit_unlock(0, &worker->create_state);
fail_release:
io_worker_release(worker);
fail:
atomic_dec(&acct->nr_running);
io_worker_ref_put(wq);
return false;
}
static void io_wq_dec_running(struct io_worker *worker)
{
struct io_wq_acct *acct = io_wq_get_acct(worker);
struct io_wq *wq = worker->wq;
if (!test_bit(IO_WORKER_F_UP, &worker->flags))
return;
if (!atomic_dec_and_test(&acct->nr_running))
return;
if (!io_acct_run_queue(acct))
return;
raw_spin_unlock(&acct->lock);
atomic_inc(&acct->nr_running);
atomic_inc(&wq->worker_refs);
io_queue_worker_create(worker, acct, create_worker_cb);
}
/*
* Worker will start processing some work. Move it to the busy list, if
* it's currently on the freelist
*/
static void __io_worker_busy(struct io_wq *wq, struct io_worker *worker)
{
if (test_bit(IO_WORKER_F_FREE, &worker->flags)) {
clear_bit(IO_WORKER_F_FREE, &worker->flags);
raw_spin_lock(&wq->lock);
hlist_nulls_del_init_rcu(&worker->nulls_node);
raw_spin_unlock(&wq->lock);
}
}
/*
* No work, worker going to sleep. Move to freelist.
*/
static void __io_worker_idle(struct io_wq *wq, struct io_worker *worker)
__must_hold(wq->lock)
{
if (!test_bit(IO_WORKER_F_FREE, &worker->flags)) {
set_bit(IO_WORKER_F_FREE, &worker->flags);
hlist_nulls_add_head_rcu(&worker->nulls_node, &wq->free_list);
}
}
static inline unsigned int io_get_work_hash(struct io_wq_work *work)
{
return atomic_read(&work->flags) >> IO_WQ_HASH_SHIFT;
}
static bool io_wait_on_hash(struct io_wq *wq, unsigned int hash)
{
bool ret = false;
spin_lock_irq(&wq->hash->wait.lock);
if (list_empty(&wq->wait.entry)) {
__add_wait_queue(&wq->hash->wait, &wq->wait);
if (!test_bit(hash, &wq->hash->map)) {
__set_current_state(TASK_RUNNING);
list_del_init(&wq->wait.entry);
ret = true;
}
}
spin_unlock_irq(&wq->hash->wait.lock);
return ret;
}
static struct io_wq_work *io_get_next_work(struct io_wq_acct *acct,
struct io_worker *worker)
__must_hold(acct->lock)
{
struct io_wq_work_node *node, *prev;
struct io_wq_work *work, *tail;
unsigned int stall_hash = -1U;
struct io_wq *wq = worker->wq;
wq_list_for_each(node, prev, &acct->work_list) {
unsigned int hash;
work = container_of(node, struct io_wq_work, list);
/* not hashed, can run anytime */
if (!io_wq_is_hashed(work)) {
wq_list_del(&acct->work_list, node, prev);
return work;
}
hash = io_get_work_hash(work);
/* all items with this hash lie in [work, tail] */
tail = wq->hash_tail[hash];
/* hashed, can run if not already running */
if (!test_and_set_bit(hash, &wq->hash->map)) {
wq->hash_tail[hash] = NULL;
wq_list_cut(&acct->work_list, &tail->list, prev);
return work;
}
if (stall_hash == -1U)
stall_hash = hash;
/* fast forward to a next hash, for-each will fix up @prev */
node = &tail->list;
}
if (stall_hash != -1U) {
bool unstalled;
/*
* Set this before dropping the lock to avoid racing with new
* work being added and clearing the stalled bit.
*/
set_bit(IO_ACCT_STALLED_BIT, &acct->flags);
raw_spin_unlock(&acct->lock);
unstalled = io_wait_on_hash(wq, stall_hash);
raw_spin_lock(&acct->lock);
if (unstalled) {
clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
if (wq_has_sleeper(&wq->hash->wait))
wake_up(&wq->hash->wait);
}
}
return NULL;
}
static void io_assign_current_work(struct io_worker *worker,
struct io_wq_work *work)
{
if (work) {
io_run_task_work();
cond_resched();
}
raw_spin_lock(&worker->lock);
worker->cur_work = work;
raw_spin_unlock(&worker->lock);
}
/*
* Called with acct->lock held, drops it before returning
*/
static void io_worker_handle_work(struct io_wq_acct *acct,
struct io_worker *worker)
__releases(&acct->lock)
{
struct io_wq *wq = worker->wq;
bool do_kill = test_bit(IO_WQ_BIT_EXIT, &wq->state);
do {
struct io_wq_work *work;
/*
* If we got some work, mark us as busy. If we didn't, but
* the list isn't empty, it means we stalled on hashed work.
* Mark us stalled so we don't keep looking for work when we
* can't make progress, any work completion or insertion will
* clear the stalled flag.
*/
work = io_get_next_work(acct, worker);
if (work) {
/*
* Make sure cancelation can find this, even before
* it becomes the active work. That avoids a window
* where the work has been removed from our general
* work list, but isn't yet discoverable as the
* current work item for this worker.
*/
raw_spin_lock(&worker->lock);
worker->cur_work = work;
raw_spin_unlock(&worker->lock);
}
raw_spin_unlock(&acct->lock);
if (!work)
break;
__io_worker_busy(wq, worker);
io_assign_current_work(worker, work);
__set_current_state(TASK_RUNNING);
/* handle a whole dependent link */
do {
struct io_wq_work *next_hashed, *linked;
unsigned int hash = io_get_work_hash(work);
next_hashed = wq_next_work(work);
if (do_kill &&
(atomic_read(&work->flags) & IO_WQ_WORK_UNBOUND))
atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
wq->do_work(work);
io_assign_current_work(worker, NULL);
linked = wq->free_work(work);
work = next_hashed;
if (!work && linked && !io_wq_is_hashed(linked)) {
work = linked;
linked = NULL;
}
io_assign_current_work(worker, work);
if (linked)
io_wq_enqueue(wq, linked);
if (hash != -1U && !next_hashed) {
/* serialize hash clear with wake_up() */
spin_lock_irq(&wq->hash->wait.lock);
clear_bit(hash, &wq->hash->map);
clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
spin_unlock_irq(&wq->hash->wait.lock);
if (wq_has_sleeper(&wq->hash->wait))
wake_up(&wq->hash->wait);
}
} while (work);
if (!__io_acct_run_queue(acct))
break;
raw_spin_lock(&acct->lock);
} while (1);
}
static int io_wq_worker(void *data)
{
struct io_worker *worker = data;
struct io_wq_acct *acct = io_wq_get_acct(worker);
struct io_wq *wq = worker->wq;
bool exit_mask = false, last_timeout = false;
char buf[TASK_COMM_LEN] = {};
set_mask_bits(&worker->flags, 0,
BIT(IO_WORKER_F_UP) | BIT(IO_WORKER_F_RUNNING));
snprintf(buf, sizeof(buf), "iou-wrk-%d", wq->task->pid);
set_task_comm(current, buf);
while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
long ret;
set_current_state(TASK_INTERRUPTIBLE);
/*
* If we have work to do, io_acct_run_queue() returns with
* the acct->lock held. If not, it will drop it.
*/
while (io_acct_run_queue(acct))
io_worker_handle_work(acct, worker);
raw_spin_lock(&wq->lock);
/*
* Last sleep timed out. Exit if we're not the last worker,
* or if someone modified our affinity.
*/
if (last_timeout && (exit_mask || acct->nr_workers > 1)) {
acct->nr_workers--;
raw_spin_unlock(&wq->lock);
__set_current_state(TASK_RUNNING);
break;
}
last_timeout = false;
__io_worker_idle(wq, worker);
raw_spin_unlock(&wq->lock);
if (io_run_task_work())
continue;
ret = schedule_timeout(WORKER_IDLE_TIMEOUT);
if (signal_pending(current)) {
struct ksignal ksig;
if (!get_signal(&ksig))
continue;
break;
}
if (!ret) {
last_timeout = true;
exit_mask = !cpumask_test_cpu(raw_smp_processor_id(),
wq->cpu_mask);
}
}
if (test_bit(IO_WQ_BIT_EXIT, &wq->state) && io_acct_run_queue(acct))
io_worker_handle_work(acct, worker);
io_worker_exit(worker);
return 0;
}
/*
* Called when a worker is scheduled in. Mark us as currently running.
*/
void io_wq_worker_running(struct task_struct *tsk)
{
struct io_worker *worker = tsk->worker_private;
if (!worker)
return;
if (!test_bit(IO_WORKER_F_UP, &worker->flags))
return;
if (test_bit(IO_WORKER_F_RUNNING, &worker->flags))
return;
set_bit(IO_WORKER_F_RUNNING, &worker->flags);
io_wq_inc_running(worker);
}
/*
* Called when worker is going to sleep. If there are no workers currently
* running and we have work pending, wake up a free one or create a new one.
*/
void io_wq_worker_sleeping(struct task_struct *tsk)
{
struct io_worker *worker = tsk->worker_private;
if (!worker)
return;
if (!test_bit(IO_WORKER_F_UP, &worker->flags))
return;
if (!test_bit(IO_WORKER_F_RUNNING, &worker->flags))
return;
clear_bit(IO_WORKER_F_RUNNING, &worker->flags);
io_wq_dec_running(worker);
}
static void io_init_new_worker(struct io_wq *wq, struct io_worker *worker,
struct task_struct *tsk)
{
tsk->worker_private = worker;
worker->task = tsk;
set_cpus_allowed_ptr(tsk, wq->cpu_mask);
raw_spin_lock(&wq->lock);
hlist_nulls_add_head_rcu(&worker->nulls_node, &wq->free_list);
list_add_tail_rcu(&worker->all_list, &wq->all_list);
set_bit(IO_WORKER_F_FREE, &worker->flags);
raw_spin_unlock(&wq->lock);
wake_up_new_task(tsk);
}
static bool io_wq_work_match_all(struct io_wq_work *work, void *data)
{
return true;
}
static inline bool io_should_retry_thread(struct io_worker *worker, long err)
{
/*
* Prevent perpetual task_work retry, if the task (or its group) is
* exiting.
*/
if (fatal_signal_pending(current))
return false;
if (worker->init_retries++ >= WORKER_INIT_LIMIT)
return false;
switch (err) {
case -EAGAIN:
case -ERESTARTSYS:
case -ERESTARTNOINTR:
case -ERESTARTNOHAND:
return true;
default:
return false;
}
}
static void queue_create_worker_retry(struct io_worker *worker)
{
/*
* We only bother retrying because there's a chance that the
* failure to create a worker is due to some temporary condition
* in the forking task (e.g. outstanding signal); give the task
* some time to clear that condition.
*/
schedule_delayed_work(&worker->work,
msecs_to_jiffies(worker->init_retries * 5));
}
static void create_worker_cont(struct callback_head *cb)
{
struct io_worker *worker;
struct task_struct *tsk;
struct io_wq *wq;
worker = container_of(cb, struct io_worker, create_work);
clear_bit_unlock(0, &worker->create_state);
wq = worker->wq;
tsk = create_io_thread(io_wq_worker, worker, NUMA_NO_NODE);
if (!IS_ERR(tsk)) {
io_init_new_worker(wq, worker, tsk);
io_worker_release(worker);
return;
} else if (!io_should_retry_thread(worker, PTR_ERR(tsk))) {
struct io_wq_acct *acct = io_wq_get_acct(worker);
atomic_dec(&acct->nr_running);
raw_spin_lock(&wq->lock);
acct->nr_workers--;
if (!acct->nr_workers) {
struct io_cb_cancel_data match = {
.fn = io_wq_work_match_all,
.cancel_all = true,
};
raw_spin_unlock(&wq->lock);
while (io_acct_cancel_pending_work(wq, acct, &match))
;
} else {
raw_spin_unlock(&wq->lock);
}
io_worker_ref_put(wq);
kfree(worker);
return;
}
/* re-create attempts grab a new worker ref, drop the existing one */
io_worker_release(worker);
queue_create_worker_retry(worker);
}
static void io_workqueue_create(struct work_struct *work)
{
struct io_worker *worker = container_of(work, struct io_worker,
work.work);
struct io_wq_acct *acct = io_wq_get_acct(worker);
if (!io_queue_worker_create(worker, acct, create_worker_cont))
kfree(worker);
}
static bool create_io_worker(struct io_wq *wq, int index)
{
struct io_wq_acct *acct = &wq->acct[index];
struct io_worker *worker;
struct task_struct *tsk;
__set_current_state(TASK_RUNNING);
worker = kzalloc(sizeof(*worker), GFP_KERNEL);
if (!worker) {
fail:
atomic_dec(&acct->nr_running);
raw_spin_lock(&wq->lock);
acct->nr_workers--;
raw_spin_unlock(&wq->lock);
io_worker_ref_put(wq);
return false;
}
refcount_set(&worker->ref, 1);
worker->wq = wq;
raw_spin_lock_init(&worker->lock);
init_completion(&worker->ref_done);
if (index == IO_WQ_ACCT_BOUND)
set_bit(IO_WORKER_F_BOUND, &worker->flags);
tsk = create_io_thread(io_wq_worker, worker, NUMA_NO_NODE);
if (!IS_ERR(tsk)) {
io_init_new_worker(wq, worker, tsk);
} else if (!io_should_retry_thread(worker, PTR_ERR(tsk))) {
kfree(worker);
goto fail;
} else {
INIT_DELAYED_WORK(&worker->work, io_workqueue_create);
queue_create_worker_retry(worker);
}
return true;
}
/*
* Iterate the passed in list and call the specific function for each
* worker that isn't exiting
*/
static bool io_wq_for_each_worker(struct io_wq *wq,
bool (*func)(struct io_worker *, void *),
void *data)
{
struct io_worker *worker;
bool ret = false;
list_for_each_entry_rcu(worker, &wq->all_list, all_list) {
if (io_worker_get(worker)) {
/* no task if node is/was offline */
if (worker->task)
ret = func(worker, data);
io_worker_release(worker);
if (ret)
break;
}
}
return ret;
}
static bool io_wq_worker_wake(struct io_worker *worker, void *data)
{
__set_notify_signal(worker->task);
wake_up_process(worker->task);
return false;
}
static void io_run_cancel(struct io_wq_work *work, struct io_wq *wq)
{
do {
atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
wq->do_work(work);
work = wq->free_work(work);
} while (work);
}
static void io_wq_insert_work(struct io_wq *wq, struct io_wq_work *work)
{
struct io_wq_acct *acct = io_work_get_acct(wq, work);
unsigned int hash;
struct io_wq_work *tail;
if (!io_wq_is_hashed(work)) {
append:
wq_list_add_tail(&work->list, &acct->work_list);
return;
}
hash = io_get_work_hash(work);
tail = wq->hash_tail[hash];
wq->hash_tail[hash] = work;
if (!tail)
goto append;
wq_list_add_after(&work->list, &tail->list, &acct->work_list);
}
static bool io_wq_work_match_item(struct io_wq_work *work, void *data)
{
return work == data;
}
void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work)
{
struct io_wq_acct *acct = io_work_get_acct(wq, work);
unsigned int work_flags = atomic_read(&work->flags);
struct io_cb_cancel_data match = {
.fn = io_wq_work_match_item,
.data = work,
.cancel_all = false,
};
bool do_create;
/*
* If io-wq is exiting for this task, or if the request has explicitly
* been marked as one that should not get executed, cancel it here.
*/
if (test_bit(IO_WQ_BIT_EXIT, &wq->state) ||
(work_flags & IO_WQ_WORK_CANCEL)) {
io_run_cancel(work, wq);
return;
}
raw_spin_lock(&acct->lock);
io_wq_insert_work(wq, work);
clear_bit(IO_ACCT_STALLED_BIT, &acct->flags);
raw_spin_unlock(&acct->lock);
rcu_read_lock();
do_create = !io_wq_activate_free_worker(wq, acct);
rcu_read_unlock();
if (do_create && ((work_flags & IO_WQ_WORK_CONCURRENT) ||
!atomic_read(&acct->nr_running))) {
bool did_create;
did_create = io_wq_create_worker(wq, acct);
if (likely(did_create))
return;
raw_spin_lock(&wq->lock);
if (acct->nr_workers) {
raw_spin_unlock(&wq->lock);
return;
}
raw_spin_unlock(&wq->lock);
/* fatal condition, failed to create the first worker */
io_acct_cancel_pending_work(wq, acct, &match);
}
}
/*
* Work items that hash to the same value will not be done in parallel.
* Used to limit concurrent writes, generally hashed by inode.
*/
void io_wq_hash_work(struct io_wq_work *work, void *val)
{
unsigned int bit;
bit = hash_ptr(val, IO_WQ_HASH_ORDER);
atomic_or(IO_WQ_WORK_HASHED | (bit << IO_WQ_HASH_SHIFT), &work->flags);
}
static bool __io_wq_worker_cancel(struct io_worker *worker,
struct io_cb_cancel_data *match,
struct io_wq_work *work)
{
if (work && match->fn(work, match->data)) {
atomic_or(IO_WQ_WORK_CANCEL, &work->flags);
__set_notify_signal(worker->task);
return true;
}
return false;
}
static bool io_wq_worker_cancel(struct io_worker *worker, void *data)
{
struct io_cb_cancel_data *match = data;
/*
* Hold the lock to avoid ->cur_work going out of scope, caller
* may dereference the passed in work.
*/
raw_spin_lock(&worker->lock);
if (__io_wq_worker_cancel(worker, match, worker->cur_work))
match->nr_running++;
raw_spin_unlock(&worker->lock);
return match->nr_running && !match->cancel_all;
}
static inline void io_wq_remove_pending(struct io_wq *wq,
struct io_wq_work *work,
struct io_wq_work_node *prev)
{
struct io_wq_acct *acct = io_work_get_acct(wq, work);
unsigned int hash = io_get_work_hash(work);
struct io_wq_work *prev_work = NULL;
if (io_wq_is_hashed(work) && work == wq->hash_tail[hash]) {
if (prev)
prev_work = container_of(prev, struct io_wq_work, list);
if (prev_work && io_get_work_hash(prev_work) == hash)
wq->hash_tail[hash] = prev_work;
else
wq->hash_tail[hash] = NULL;
}
wq_list_del(&acct->work_list, &work->list, prev);
}
static bool io_acct_cancel_pending_work(struct io_wq *wq,
struct io_wq_acct *acct,
struct io_cb_cancel_data *match)
{
struct io_wq_work_node *node, *prev;
struct io_wq_work *work;
raw_spin_lock(&acct->lock);
wq_list_for_each(node, prev, &acct->work_list) {
work = container_of(node, struct io_wq_work, list);
if (!match->fn(work, match->data))
continue;
io_wq_remove_pending(wq, work, prev);
raw_spin_unlock(&acct->lock);
io_run_cancel(work, wq);
match->nr_pending++;
/* not safe to continue after unlock */
return true;
}
raw_spin_unlock(&acct->lock);
return false;
}
static void io_wq_cancel_pending_work(struct io_wq *wq,
struct io_cb_cancel_data *match)
{
int i;
retry:
for (i = 0; i < IO_WQ_ACCT_NR; i++) {
struct io_wq_acct *acct = io_get_acct(wq, i == 0);
if (io_acct_cancel_pending_work(wq, acct, match)) {
if (match->cancel_all)
goto retry;
break;
}
}
}
static void io_wq_cancel_running_work(struct io_wq *wq,
struct io_cb_cancel_data *match)
{
rcu_read_lock();
io_wq_for_each_worker(wq, io_wq_worker_cancel, match);
rcu_read_unlock();
}
enum io_wq_cancel io_wq_cancel_cb(struct io_wq *wq, work_cancel_fn *cancel,
void *data, bool cancel_all)
{
struct io_cb_cancel_data match = {
.fn = cancel,
.data = data,
.cancel_all = cancel_all,
};
/*
* First check pending list, if we're lucky we can just remove it
* from there. CANCEL_OK means that the work is returned as-new,
* no completion will be posted for it.
*
* Then check if a free (going busy) or busy worker has the work
* currently running. If we find it there, we'll return CANCEL_RUNNING
* as an indication that we attempt to signal cancellation. The
* completion will run normally in this case.
*
* Do both of these while holding the wq->lock, to ensure that
* we'll find a work item regardless of state.
*/
io_wq_cancel_pending_work(wq, &match);
if (match.nr_pending && !match.cancel_all)
return IO_WQ_CANCEL_OK;
raw_spin_lock(&wq->lock);
io_wq_cancel_running_work(wq, &match);
raw_spin_unlock(&wq->lock);
if (match.nr_running && !match.cancel_all)
return IO_WQ_CANCEL_RUNNING;
if (match.nr_running)
return IO_WQ_CANCEL_RUNNING;
if (match.nr_pending)
return IO_WQ_CANCEL_OK;
return IO_WQ_CANCEL_NOTFOUND;
}
static int io_wq_hash_wake(struct wait_queue_entry *wait, unsigned mode,
int sync, void *key)
{
struct io_wq *wq = container_of(wait, struct io_wq, wait);
int i;
list_del_init(&wait->entry);
rcu_read_lock();
for (i = 0; i < IO_WQ_ACCT_NR; i++) {
struct io_wq_acct *acct = &wq->acct[i];
if (test_and_clear_bit(IO_ACCT_STALLED_BIT, &acct->flags))
io_wq_activate_free_worker(wq, acct);
}
rcu_read_unlock();
return 1;
}
struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data)
{
int ret, i;
struct io_wq *wq;
if (WARN_ON_ONCE(!data->free_work || !data->do_work))
return ERR_PTR(-EINVAL);
if (WARN_ON_ONCE(!bounded))
return ERR_PTR(-EINVAL);
wq = kzalloc(sizeof(struct io_wq), GFP_KERNEL);
if (!wq)
return ERR_PTR(-ENOMEM);
refcount_inc(&data->hash->refs);
wq->hash = data->hash;
wq->free_work = data->free_work;
wq->do_work = data->do_work;
ret = -ENOMEM;
if (!alloc_cpumask_var(&wq->cpu_mask, GFP_KERNEL))
goto err;
cpuset_cpus_allowed(data->task, wq->cpu_mask);
wq->acct[IO_WQ_ACCT_BOUND].max_workers = bounded;
wq->acct[IO_WQ_ACCT_UNBOUND].max_workers =
task_rlimit(current, RLIMIT_NPROC);
INIT_LIST_HEAD(&wq->wait.entry);
wq->wait.func = io_wq_hash_wake;
for (i = 0; i < IO_WQ_ACCT_NR; i++) {
struct io_wq_acct *acct = &wq->acct[i];
acct->index = i;
atomic_set(&acct->nr_running, 0);
INIT_WQ_LIST(&acct->work_list);
raw_spin_lock_init(&acct->lock);
}
raw_spin_lock_init(&wq->lock);
INIT_HLIST_NULLS_HEAD(&wq->free_list, 0);
INIT_LIST_HEAD(&wq->all_list);
wq->task = get_task_struct(data->task);
atomic_set(&wq->worker_refs, 1);
init_completion(&wq->worker_done);
ret = cpuhp_state_add_instance_nocalls(io_wq_online, &wq->cpuhp_node);
if (ret)
goto err;
return wq;
err:
io_wq_put_hash(data->hash);
free_cpumask_var(wq->cpu_mask);
kfree(wq);
return ERR_PTR(ret);
}
static bool io_task_work_match(struct callback_head *cb, void *data)
{
struct io_worker *worker;
if (cb->func != create_worker_cb && cb->func != create_worker_cont)
return false;
worker = container_of(cb, struct io_worker, create_work);
return worker->wq == data;
}
void io_wq_exit_start(struct io_wq *wq)
{
set_bit(IO_WQ_BIT_EXIT, &wq->state);
}
static void io_wq_cancel_tw_create(struct io_wq *wq)
{
struct callback_head *cb;
while ((cb = task_work_cancel_match(wq->task, io_task_work_match, wq)) != NULL) {
struct io_worker *worker;
worker = container_of(cb, struct io_worker, create_work);
io_worker_cancel_cb(worker);
/*
* Only the worker continuation helper has worker allocated and
* hence needs freeing.
*/
if (cb->func == create_worker_cont)
kfree(worker);
}
}
static void io_wq_exit_workers(struct io_wq *wq)
{
if (!wq->task)
return;
io_wq_cancel_tw_create(wq);
rcu_read_lock();
io_wq_for_each_worker(wq, io_wq_worker_wake, NULL);
rcu_read_unlock();
io_worker_ref_put(wq);
wait_for_completion(&wq->worker_done);
spin_lock_irq(&wq->hash->wait.lock);
list_del_init(&wq->wait.entry);
spin_unlock_irq(&wq->hash->wait.lock);
put_task_struct(wq->task);
wq->task = NULL;
}
static void io_wq_destroy(struct io_wq *wq)
{
struct io_cb_cancel_data match = {
.fn = io_wq_work_match_all,
.cancel_all = true,
};
cpuhp_state_remove_instance_nocalls(io_wq_online, &wq->cpuhp_node);
io_wq_cancel_pending_work(wq, &match);
free_cpumask_var(wq->cpu_mask);
io_wq_put_hash(wq->hash);
kfree(wq);
}
void io_wq_put_and_exit(struct io_wq *wq)
{
WARN_ON_ONCE(!test_bit(IO_WQ_BIT_EXIT, &wq->state));
io_wq_exit_workers(wq);
io_wq_destroy(wq);
}
struct online_data {
unsigned int cpu;
bool online;
};
static bool io_wq_worker_affinity(struct io_worker *worker, void *data)
{
struct online_data *od = data;
if (od->online)
cpumask_set_cpu(od->cpu, worker->wq->cpu_mask);
else
cpumask_clear_cpu(od->cpu, worker->wq->cpu_mask);
return false;
}
static int __io_wq_cpu_online(struct io_wq *wq, unsigned int cpu, bool online)
{
struct online_data od = {
.cpu = cpu,
.online = online
};
rcu_read_lock();
io_wq_for_each_worker(wq, io_wq_worker_affinity, &od);
rcu_read_unlock();
return 0;
}
static int io_wq_cpu_online(unsigned int cpu, struct hlist_node *node)
{
struct io_wq *wq = hlist_entry_safe(node, struct io_wq, cpuhp_node);
return __io_wq_cpu_online(wq, cpu, true);
}
static int io_wq_cpu_offline(unsigned int cpu, struct hlist_node *node)
{
struct io_wq *wq = hlist_entry_safe(node, struct io_wq, cpuhp_node);
return __io_wq_cpu_online(wq, cpu, false);
}
int io_wq_cpu_affinity(struct io_uring_task *tctx, cpumask_var_t mask)
{
cpumask_var_t allowed_mask;
int ret = 0;
if (!tctx || !tctx->io_wq)
return -EINVAL;
if (!alloc_cpumask_var(&allowed_mask, GFP_KERNEL))
return -ENOMEM;
rcu_read_lock();
cpuset_cpus_allowed(tctx->io_wq->task, allowed_mask);
if (mask) {
if (cpumask_subset(mask, allowed_mask))
cpumask_copy(tctx->io_wq->cpu_mask, mask);
else
ret = -EINVAL;
} else {
cpumask_copy(tctx->io_wq->cpu_mask, allowed_mask);
}
rcu_read_unlock();
free_cpumask_var(allowed_mask);
return ret;
}
/*
* Set max number of unbounded workers, returns old value. If new_count is 0,
* then just return the old value.
*/
int io_wq_max_workers(struct io_wq *wq, int *new_count)
{
struct io_wq_acct *acct;
int prev[IO_WQ_ACCT_NR];
int i;
BUILD_BUG_ON((int) IO_WQ_ACCT_BOUND != (int) IO_WQ_BOUND);
BUILD_BUG_ON((int) IO_WQ_ACCT_UNBOUND != (int) IO_WQ_UNBOUND);
BUILD_BUG_ON((int) IO_WQ_ACCT_NR != 2);
for (i = 0; i < IO_WQ_ACCT_NR; i++) {
if (new_count[i] > task_rlimit(current, RLIMIT_NPROC))
new_count[i] = task_rlimit(current, RLIMIT_NPROC);
}
for (i = 0; i < IO_WQ_ACCT_NR; i++)
prev[i] = 0;
rcu_read_lock();
raw_spin_lock(&wq->lock);
for (i = 0; i < IO_WQ_ACCT_NR; i++) {
acct = &wq->acct[i];
prev[i] = max_t(int, acct->max_workers, prev[i]);
if (new_count[i])
acct->max_workers = new_count[i];
}
raw_spin_unlock(&wq->lock);
rcu_read_unlock();
for (i = 0; i < IO_WQ_ACCT_NR; i++)
new_count[i] = prev[i];
return 0;
}
static __init int io_wq_init(void)
{
int ret;
ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "io-wq/online",
io_wq_cpu_online, io_wq_cpu_offline);
if (ret < 0)
return ret;
io_wq_online = ret;
return 0;
}
subsys_initcall(io_wq_init);
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