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io_uring: replace inflight_wait with tctx->wait 

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>
This commit is contained in:
Pavel Begunkov 2020-11-15 12:56:32 +00:00 committed by Jens Axboe
parent 10cad2c40d
commit c98de08c99
1 changed files with 6 additions and 7 deletions
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13
fs/io_uring.c
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@ -287,7 +287,6 @@ 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;
@ -1291,7 +1290,6 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
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);
@ -6046,12 +6044,13 @@ static int io_req_defer(struct io_kiocb *req, const struct io_uring_sqe *sqe)
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;
spin_lock_irqsave(&ctx->inflight_lock, flags);
list_del(&req->inflight_entry);
if (waitqueue_active(&ctx->inflight_wait))
wake_up(&ctx->inflight_wait);
if (atomic_read(&tctx->in_idle))
wake_up(&tctx->wait);
spin_unlock_irqrestore(&ctx->inflight_lock, flags);
req->flags &= ~REQ_F_INFLIGHT;
put_files_struct(req->work.identity->files);
@ -8693,8 +8692,8 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
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 */
@ -8707,7 +8706,7 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
/* cancellations _may_ trigger task work */
io_run_task_work();
schedule();
finish_wait(&ctx->inflight_wait, &wait);
finish_wait(&task->io_uring->wait, &wait);
}
}