linux-kernel - Re: Pending splice(file -> FIFO) excludes all other FIFO operations forever (was: ... always blocks read(FIFO), regardless of O

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Date:   Sat, 8 Jul 2023 01:00:29 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Ahelenia Ziemiańska 
        <nabijaczleweli@...ijaczleweli.xyz>,
        Christian Brauner <brauner@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        David Howells <dhowells@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Pending splice(file -> FIFO) excludes all other FIFO operations
 forever (was: ... always blocks read(FIFO), regardless of O_NONBLOCK on read
 side?)

On Thu, Jul 06, 2023 at 02:56:45PM -0700, Linus Torvalds wrote:
> +static int busy_pipe_buf_confirm(struct pipe_inode_info *pipe,
> +				 struct pipe_buffer *buf)
> +{
> +	struct page *page = buf->page;
> +
> +	if (folio_wait_bit_interruptible(page_folio(page), PG_locked))
> +		return -EINTR;

Do we really want interruptible here rather than killable?  That is,
do we want SIGWINCH or SIGALRM to result in a short read?  I assume
it's OK to return a short read because userspace has explicitly asked
for O_NONBLOCK and can therefore be expected to actually check the
return value from read().