[PATCH AUTOSEL 5.7 206/274] io_uring: allow POLL_ADD with double poll_wait() users

Sasha Levin
2020-06-08T23:12:32Z

From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 18bceab101adde8f38de76016bc77f3f25cf22f4 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 218 +++++++++++++++++++++++++++++++++-----------------
1 file changed, 146 insertions(+), 72 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 03147b6694fd..dd90c3fcd4f5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4096,27 +4096,6 @@ 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)
{
@@ -4170,6 +4149,144 @@ 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);
@@ -4245,18 +4362,13 @@ 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);
@@ -4287,6 +4399,7 @@ 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;
@@ -4301,6 +4414,7 @@ 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;
@@ -4320,7 +4434,9 @@ 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);
@@ -4353,6 +4469,7 @@ 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 {
struct async_poll *apoll = req->apoll;
@@ -4453,49 +4570,6 @@ 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)
{
--
2.25.1