linux-kernel - Re: [PATCH 1/2] pipe: change pipe_write() to never add a zero-sized buffer

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Message-ID: <20250209191510.GB27435@redhat.com>
Date: Sun, 9 Feb 2025 20:15:11 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christian Brauner <brauner@...nel.org>,
	Jeff Layton <jlayton@...nel.org>,
	David Howells <dhowells@...hat.com>,
	"Gautham R. Shenoy" <gautham.shenoy@....com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Mateusz Guzik <mjguzik@...il.com>,
	Neeraj Upadhyay <Neeraj.Upadhyay@....com>,
	Oliver Sang <oliver.sang@...el.com>,
	Swapnil Sapkal <swapnil.sapkal@....com>,
	WangYuli <wangyuli@...ontech.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] pipe: change pipe_write() to never add a zero-sized
 buffer

On 02/09, Linus Torvalds wrote:
>
> On Sun, 9 Feb 2025 at 10:45, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Again, lets look eat_empty_buffer().
> >
> > The comment says "maybe it's empty" but how/why can this happen ?
>
> WHY DO YOU CARE?

Because it looks unclear/confusing, and I think it can confuse other
readers of this code. Especially after 1/2.

> So here's the deal: either you
...
>  (b) you DON'T convince yourself that that is true, and you leave
> eat_empty_buffer() alone.

Yes, I failed to convince myself that fs/splice.c can never add an
empty bufer. Although it seems to me it should not.

> In contrast, the "eat_empty_buffer()" case just saying "if it's an
> empty buffer, it doesn't satisfy my needs, so I'll just release the
> empty buffer and go on".

... without wakeup_pipe_writers().

OK, nevermind, I see your point even if I do not 100% agree.

I'll send v2 without WARN_ON() and without 2/2.

Oleg.