Re: aio poll, io_pgetevents and a new in-kernel poll API V3

Christoph Hellwig
2018-01-18T17:42:31Z

On Thu, Jan 18, 2018 at 11:44:03AM -0500, Jeff Moyer wrote:
> Jeff Moyer <jmoyer@redhat.com> writes:
>
> > FYI, this kernel has issues. It will boot up, but I don't have
> > networking, and even rebooting doesn't succeed. I'm looking into it.
>
> A bisect lands on: eventfd: switch to ->poll_mask. That's not super
> helpful, though. I did run the ltp eventfd2 tests, and they all pass.
>
> The actual issue I get on boot is that several services don't start:
>
> [...]
>
> Christoph, are you able to reproduce this?

No, I can't reproduce any of that. But I don't have a Fedora system
either, so this might be a new systemd version doing funky things.

The major change in this version was to call ->poll_mask before setting up
the wait queue as well. This does the right thing for poll and aio poll,
but the more I dig into the epoll code the less sure I am it does the right
thing for it, or in fact that epoll does the right thing in general..

Do you still see it with the patch below applied?

diff --git a/fs/select.c b/fs/select.c
index 707abe79536b..1784c1a29253 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -53,9 +53,9 @@ __poll_t vfs_poll(struct file *file, struct poll_table_struct *pt)
head = vfs_get_poll_head(file, events);
if (!head)
return DEFAULT_POLLMASK;
- mask = file->f_op->poll_mask(file, events);
- if (mask)
- return mask;
+// mask = file->f_op->poll_mask(file, events);
+// if (mask)
+// return mask;

pt->_qproc(file, head, pt);
}