Re: liburing 500f9fbadef8-test test failure on top-of-tree

[Jens Axboe <axboe@kernel.dk>]

On 5/19/20 3:58 PM, Jeff Moyer wrote:
> Hi,
> 
> This test case is failing for me when run atop a dm device.  The test
> sets up a ring with IO_SETUP_IOPOLL, creates a file and opens it with
> O_DIRECT, and then issues a writev.  The writev operation is returning
> -22 (-EINVAL).  The failure comes from this check inside io_import_iov:
> 
> 	/* buffer index only valid with fixed read/write, or buffer select  */
>         if (req->rw.kiocb.private && !(req->flags & REQ_F_BUFFER_SELECT))
>                 return -EINVAL;
> 
> req->rw.kiocb.private is being used by the iomap code to store a pointer
> to the request queue.  The sequence of events is as follows:
> 
> io_write is called in the context of the system call, it calls
> call_write_iter, which returns -EAGAIN.  The I/O is punted to a
> workqueue.
> 
> The work item then tries to issue the I/O after clearing IOCB_NOWAIT,
> and for some reason fails again with -EAGAIN.
> 
> On the *third* call to io_write, the private pointer has been
> overwitten, and we trigger the above -EINVAL return.
> 
> I have no idea why we're getting EAGAIN on the first call in the
> workqueue context, so I'm not sure if that's the problem, of if we
> simply can't use the kiocb.private pointer for this purpose.  It seems
> clear that once we've called into the iomap code, we can't rely on the
> contents of kiocb.private.
> 
> Jens, what do you think?

See: https://lore.kernel.org/io-uring/1589925170-48687-1-git-send-email-bijan.mottahedeh@oracle.com/T/#m9cec13d26c0b2db03889e1b36c9bcc20f4f8244a

-- 
Jens Axboe