Re: [PATCH 1/2] aio: keep poll requests on waitqueue until completed

On Fri, Dec 03, 2021 at 04:23:00PM -0800, Eric Biggers wrote:

@@ -1680,20 +1690,24 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync, if (mask && !(mask & req->events)) return 0;

• list_del_init(&req->wait.entry);

• /*

• * Complete the iocb inline if possible.  This requires that two
  

• * conditions be met:
  

• *   1. The event mask must have been passed.  If a regular wakeup was
  

• *	done instead, then mask == 0 and we have to call vfs_poll() to
  

• *	get the events, so inline completion isn't possible.
  

• *   2. ctx_lock must not be busy.  We have to use trylock because we
  

• *      already hold the waitqueue lock, so this inverts the normal
  

• *      locking order.  Use irqsave/irqrestore because not all
  

• *      filesystems (e.g. fuse) call this function with IRQs disabled,
  

• *      yet IRQs have to be disabled before ctx_lock is obtained.
  

• */
  

  if (mask && spin_trylock_irqsave(&iocb->ki_ctx->ctx_lock, flags)) { struct kioctx *ctx = iocb->ki_ctx;

• /*
  

•  * Try to complete the iocb inline if we can. Use
  

•  * irqsave/irqrestore because not all filesystems (e.g. fuse)
  

•  * call this function with IRQs disabled and because IRQs
  

•  * have to be disabled before ctx_lock is obtained.
  

•  */
  

• list_del_init(&req->wait.entry);
  

  list_del(&iocb->ki_list); iocb->ki_res.res = mangle_poll(mask);

• req->done = true;
  

  if (iocb->ki_eventfd && eventfd_signal_allowed()) { iocb = NULL; INIT_WORK(&req->work, aio_poll_put_work);

@@ -1703,7 +1717,16 @@ static int aio_poll_wake(struct wait_queue_entry *wait, unsigned mode, int sync, if (iocb) iocb_put(iocb); } else {

I think I missed something here. Now that the request is left on the waitqueue, there needs to be a third condition for completing the iocb inline: the completion work must not have already been scheduled.

- Eric