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io_uring: allow POLL_ADD with double poll_wait() users 

Some file descriptors use separate waitqueues for their f_ops->poll()
handler, most commonly one for read and one for write. The io_uring
poll implementation doesn't work with that, as the 2nd poll_wait()
call will cause the io_uring poll request to -EINVAL.

This affects (at least) tty devices and /dev/random as well. This is a
big problem for event loops where some file descriptors work, and others
don't.

With this fix, io_uring handles multiple waitqueues.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-05-15 11:56:54 -06:00
parent 4a38aed2a0
commit 18bceab101
1 changed files with 146 additions and 72 deletions
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218
fs/io_uring.c
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@ -4099,27 +4099,6 @@ struct io_poll_table {
int error;
};
static void __io_queue_proc(struct io_poll_iocb *poll, struct io_poll_table *pt,
struct wait_queue_head *head)
{
if (unlikely(poll->head)) {
pt->error = -EINVAL;
return;
}
pt->error = 0;
poll->head = head;
add_wait_queue(head, &poll->wait);
}
static void io_async_queue_proc(struct file *file, struct wait_queue_head *head,
struct poll_table_struct *p)
{
struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
__io_queue_proc(&pt->req->apoll->poll, pt, head);
}
static int __io_async_wake(struct io_kiocb *req, struct io_poll_iocb *poll,
__poll_t mask, task_work_func_t func)
{
@ -4171,6 +4150,144 @@ static bool io_poll_rewait(struct io_kiocb *req, struct io_poll_iocb *poll)
return false;
}
static void io_poll_remove_double(struct io_kiocb *req)
{
struct io_poll_iocb *poll = (struct io_poll_iocb *) req->io;
lockdep_assert_held(&req->ctx->completion_lock);
if (poll && poll->head) {
struct wait_queue_head *head = poll->head;
spin_lock(&head->lock);
list_del_init(&poll->wait.entry);
if (poll->wait.private)
refcount_dec(&req->refs);
poll->head = NULL;
spin_unlock(&head->lock);
}
}
static void io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
{
struct io_ring_ctx *ctx = req->ctx;
io_poll_remove_double(req);
req->poll.done = true;
io_cqring_fill_event(req, error ? error : mangle_poll(mask));
io_commit_cqring(ctx);
}
static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt)
{
struct io_ring_ctx *ctx = req->ctx;
if (io_poll_rewait(req, &req->poll)) {
spin_unlock_irq(&ctx->completion_lock);
return;
}
hash_del(&req->hash_node);
io_poll_complete(req, req->result, 0);
req->flags |= REQ_F_COMP_LOCKED;
io_put_req_find_next(req, nxt);
spin_unlock_irq(&ctx->completion_lock);
io_cqring_ev_posted(ctx);
}
static void io_poll_task_func(struct callback_head *cb)
{
struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
struct io_kiocb *nxt = NULL;
io_poll_task_handler(req, &nxt);
if (nxt) {
struct io_ring_ctx *ctx = nxt->ctx;
mutex_lock(&ctx->uring_lock);
__io_queue_sqe(nxt, NULL);
mutex_unlock(&ctx->uring_lock);
}
}
static int io_poll_double_wake(struct wait_queue_entry *wait, unsigned mode,
int sync, void *key)
{
struct io_kiocb *req = wait->private;
struct io_poll_iocb *poll = (struct io_poll_iocb *) req->io;
__poll_t mask = key_to_poll(key);
/* for instances that support it check for an event match first: */
if (mask && !(mask & poll->events))
return 0;
if (req->poll.head) {
bool done;
spin_lock(&req->poll.head->lock);
done = list_empty(&req->poll.wait.entry);
if (!done)
list_del_init(&req->poll.wait.entry);
spin_unlock(&req->poll.head->lock);
if (!done)
__io_async_wake(req, poll, mask, io_poll_task_func);
}
refcount_dec(&req->refs);
return 1;
}
static void io_init_poll_iocb(struct io_poll_iocb *poll, __poll_t events,
wait_queue_func_t wake_func)
{
poll->head = NULL;
poll->done = false;
poll->canceled = false;
poll->events = events;
INIT_LIST_HEAD(&poll->wait.entry);
init_waitqueue_func_entry(&poll->wait, wake_func);
}
static void __io_queue_proc(struct io_poll_iocb *poll, struct io_poll_table *pt,
struct wait_queue_head *head)
{
struct io_kiocb *req = pt->req;
/*
* If poll->head is already set, it's because the file being polled
* uses multiple waitqueues for poll handling (eg one for read, one
* for write). Setup a separate io_poll_iocb if this happens.
*/
if (unlikely(poll->head)) {
/* already have a 2nd entry, fail a third attempt */
if (req->io) {
pt->error = -EINVAL;
return;
}
poll = kmalloc(sizeof(*poll), GFP_ATOMIC);
if (!poll) {
pt->error = -ENOMEM;
return;
}
io_init_poll_iocb(poll, req->poll.events, io_poll_double_wake);
refcount_inc(&req->refs);
poll->wait.private = req;
req->io = (void *) poll;
}
pt->error = 0;
poll->head = head;
add_wait_queue(head, &poll->wait);
}
static void io_async_queue_proc(struct file *file, struct wait_queue_head *head,
struct poll_table_struct *p)
{
struct io_poll_table *pt = container_of(p, struct io_poll_table, pt);
__io_queue_proc(&pt->req->apoll->poll, pt, head);
}
static void io_async_task_func(struct callback_head *cb)
{
struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
@ -4246,18 +4363,13 @@ static __poll_t __io_arm_poll_handler(struct io_kiocb *req,
bool cancel = false;
poll->file = req->file;
poll->head = NULL;
poll->done = poll->canceled = false;
poll->events = mask;
io_init_poll_iocb(poll, mask, wake_func);
poll->wait.private = req;
ipt->pt._key = mask;
ipt->req = req;
ipt->error = -EINVAL;
INIT_LIST_HEAD(&poll->wait.entry);
init_waitqueue_func_entry(&poll->wait, wake_func);
poll->wait.private = req;
mask = vfs_poll(req->file, &ipt->pt) & poll->events;
spin_lock_irq(&ctx->completion_lock);
@ -4288,6 +4400,7 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
struct async_poll *apoll;
struct io_poll_table ipt;
__poll_t mask, ret;
bool had_io;
if (!req->file || !file_can_poll(req->file))
return false;
@ -4302,6 +4415,7 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
req->flags |= REQ_F_POLLED;
memcpy(&apoll->work, &req->work, sizeof(req->work));
had_io = req->io != NULL;
get_task_struct(current);
req->task = current;
@ -4321,7 +4435,9 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
io_async_wake);
if (ret) {
ipt.error = 0;
apoll->poll.done = true;
/* only remove double add if we did it here */
if (!had_io)
io_poll_remove_double(req);
spin_unlock_irq(&ctx->completion_lock);
memcpy(&req->work, &apoll->work, sizeof(req->work));
kfree(apoll);
@ -4354,6 +4470,7 @@ static bool io_poll_remove_one(struct io_kiocb *req)
bool do_complete;
if (req->opcode == IORING_OP_POLL_ADD) {
io_poll_remove_double(req);
do_complete = __io_poll_remove_one(req, &req->poll);
} else {
apoll = req->apoll;
@ -4455,49 +4572,6 @@ static int io_poll_remove(struct io_kiocb *req)
return 0;
}
static void io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
{
struct io_ring_ctx *ctx = req->ctx;
req->poll.done = true;
io_cqring_fill_event(req, error ? error : mangle_poll(mask));
io_commit_cqring(ctx);
}
static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt)
{
struct io_ring_ctx *ctx = req->ctx;
struct io_poll_iocb *poll = &req->poll;
if (io_poll_rewait(req, poll)) {
spin_unlock_irq(&ctx->completion_lock);
return;
}
hash_del(&req->hash_node);
io_poll_complete(req, req->result, 0);
req->flags |= REQ_F_COMP_LOCKED;
io_put_req_find_next(req, nxt);
spin_unlock_irq(&ctx->completion_lock);
io_cqring_ev_posted(ctx);
}
static void io_poll_task_func(struct callback_head *cb)
{
struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
struct io_kiocb *nxt = NULL;
io_poll_task_handler(req, &nxt);
if (nxt) {
struct io_ring_ctx *ctx = nxt->ctx;
mutex_lock(&ctx->uring_lock);
__io_queue_sqe(nxt, NULL);
mutex_unlock(&ctx->uring_lock);
}
}
static int io_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync,
void *key)
{