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

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Message-ID: <x49o9lrt5d3.fsf@segfault.boston.devel.redhat.com>
Date:   Thu, 18 Jan 2018 12:59:52 -0500
From:   Jeff Moyer <jmoyer@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     viro@...iv.linux.org.uk, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        netdev@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: aio poll, io_pgetevents and a new in-kernel poll API V3

Christoph Hellwig <hch@....de> writes:

> On Thu, Jan 18, 2018 at 11:44:03AM -0500, Jeff Moyer wrote:
>> Jeff Moyer <jmoyer@...hat.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?

No, that fixes it for me.

-Jeff

> 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);
>  	}