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io_uring: fix mis-refcounting linked timeouts 

io_prep_linked_timeout() sets REQ_F_LINK_TIMEOUT altering refcounting of
the following linked request. After that someone should call
io_queue_linked_timeout(), otherwise a submission reference of the linked
timeout won't be ever dropped.

That's what happens in io_steal_work() if io-wq decides to postpone linked
request with io_wqe_enqueue(). io_queue_linked_timeout() can also be
potentially called twice without synchronisation during re-submission,
e.g. io_rw_resubmit().

There are the rules, whoever did io_prep_linked_timeout() must also call
io_queue_linked_timeout(). To not do it twice, io_prep_linked_timeout()
will return non NULL only for the first call. That's controlled by
REQ_F_LINK_TIMEOUT flag.

Also kill REQ_F_QUEUE_TIMEOUT.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2020-07-03 22:15:06 +03:00 committed by Jens Axboe
parent c2c4c83c58
commit 6df1db6b54
1 changed files with 7 additions and 26 deletions
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33
fs/io_uring.c
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@ -538,7 +538,6 @@ enum {
REQ_F_POLLED_BIT,
REQ_F_BUFFER_SELECTED_BIT,
REQ_F_NO_FILE_TABLE_BIT,
REQ_F_QUEUE_TIMEOUT_BIT,
REQ_F_WORK_INITIALIZED_BIT,
REQ_F_TASK_PINNED_BIT,
@ -586,8 +585,6 @@ enum {
REQ_F_BUFFER_SELECTED = BIT(REQ_F_BUFFER_SELECTED_BIT),
/* doesn't need file table for this request */
REQ_F_NO_FILE_TABLE = BIT(REQ_F_NO_FILE_TABLE_BIT),
/* needs to queue linked timeout */
REQ_F_QUEUE_TIMEOUT = BIT(REQ_F_QUEUE_TIMEOUT_BIT),
/* io_wq_work is initialized */
REQ_F_WORK_INITIALIZED = BIT(REQ_F_WORK_INITIALIZED_BIT),
/* req->task is refcounted */
@ -1842,7 +1839,7 @@ static void io_put_req(struct io_kiocb *req)
static struct io_wq_work *io_steal_work(struct io_kiocb *req)
{
struct io_kiocb *timeout, *nxt = NULL;
struct io_kiocb *nxt;
/*
* A ref is owned by io-wq in which context we're. So, if that's the
@ -1853,13 +1850,7 @@ static struct io_wq_work *io_steal_work(struct io_kiocb *req)
return NULL;
nxt = io_req_find_next(req);
if (!nxt)
return NULL;
timeout = io_prep_linked_timeout(nxt);
if (timeout)
nxt->flags |= REQ_F_QUEUE_TIMEOUT;
return &nxt->work;
return nxt ? &nxt->work : NULL;
}
/*
@ -5702,24 +5693,15 @@ static int io_issue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe,
return 0;
}
static void io_arm_async_linked_timeout(struct io_kiocb *req)
{
struct io_kiocb *link;
/* link head's timeout is queued in io_queue_async_work() */
if (!(req->flags & REQ_F_QUEUE_TIMEOUT))
return;
link = list_first_entry(&req->link_list, struct io_kiocb, link_list);
io_queue_linked_timeout(link);
}
static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
{
struct io_kiocb *req = container_of(work, struct io_kiocb, work);
struct io_kiocb *timeout;
int ret = 0;
io_arm_async_linked_timeout(req);
timeout = io_prep_linked_timeout(req);
if (timeout)
io_queue_linked_timeout(timeout);
/* if NO_CANCEL is set, we must still run the work */
if ((work->flags & (IO_WQ_WORK_CANCEL|IO_WQ_WORK_NO_CANCEL)) ==
@ -5893,8 +5875,7 @@ static struct io_kiocb *io_prep_linked_timeout(struct io_kiocb *req)
if (!(req->flags & REQ_F_LINK_HEAD))
return NULL;
/* for polled retry, if flag is set, we already went through here */
if (req->flags & REQ_F_POLLED)
if (req->flags & REQ_F_LINK_TIMEOUT)
return NULL;
nxt = list_first_entry_or_null(&req->link_list, struct io_kiocb,