[PATCH 5.10 10/54] io_uring: replace inflight_wait with tctx->wait

Greg Kroah-Hartman
2021-02-11T15:31:10Z

From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit c98de08c990e190fc7cc3aaf8079b4a0674c6425 ]

As tasks now cancel only theirs requests, and inflight_wait is awaited
only in io_uring_cancel_files(), which should be called with ->in_idle
set, instead of keeping a separate inflight_wait use tctx->wait.

That will add some spurious wakeups but actually is safer from point of
not hanging the task.

e.g.
task1 | IRQ
| *start* io_complete_rw_common(link)
| link: req1 -> req2 -> req3(with files)
*cancel_files() |
io_wq_cancel(), etc. |
| put_req(link), adds to io-wq req2
schedule() |

So, task1 will never try to cancel req2 or req3. If req2 is
long-standing (e.g. read(empty_pipe)), this may hang.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/io_uring.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -286,7 +286,6 @@ struct io_ring_ctx {
struct list_head timeout_list;
struct list_head cq_overflow_list;

- wait_queue_head_t inflight_wait;
struct io_uring_sqe *sq_sqes;
} ____cacheline_aligned_in_smp;

@@ -1220,7 +1219,6 @@ static struct io_ring_ctx *io_ring_ctx_a
INIT_LIST_HEAD(&ctx->iopoll_list);
INIT_LIST_HEAD(&ctx->defer_list);
INIT_LIST_HEAD(&ctx->timeout_list);
- init_waitqueue_head(&ctx->inflight_wait);
spin_lock_init(&ctx->inflight_lock);
INIT_LIST_HEAD(&ctx->inflight_list);
INIT_DELAYED_WORK(&ctx->file_put_work, io_file_put_work);
@@ -5894,6 +5892,7 @@ static int io_req_defer(struct io_kiocb
static void io_req_drop_files(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
+ struct io_uring_task *tctx = req->task->io_uring;
unsigned long flags;

if (req->work.flags & IO_WQ_WORK_FILES) {
@@ -5905,8 +5904,8 @@ static void io_req_drop_files(struct io_
spin_unlock_irqrestore(&ctx->inflight_lock, flags);
req->flags &= ~REQ_F_INFLIGHT;
req->work.flags &= ~IO_WQ_WORK_FILES;
- if (waitqueue_active(&ctx->inflight_wait))
- wake_up(&ctx->inflight_wait);
+ if (atomic_read(&tctx->in_idle))
+ wake_up(&tctx->wait);
}

static void __io_clean_op(struct io_kiocb *req)
@@ -8605,8 +8604,8 @@ static void io_uring_cancel_files(struct
break;
}
if (found)
- prepare_to_wait(&ctx->inflight_wait, &wait,
- TASK_UNINTERRUPTIBLE);
+ prepare_to_wait(&task->io_uring->wait, &wait,
+ TASK_UNINTERRUPTIBLE);
spin_unlock_irq(&ctx->inflight_lock);

/* We need to keep going until we don't find a matching req */
@@ -8619,7 +8618,7 @@ static void io_uring_cancel_files(struct
/* cancellations _may_ trigger task work */
io_run_task_work();
schedule();
- finish_wait(&ctx->inflight_wait, &wait);
+ finish_wait(&task->io_uring->wait, &wait);
}
}