linux-kernel - Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still full

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Message-ID: <20250307112920.GB5963@redhat.com>
Date: Fri, 7 Mar 2025 12:29:21 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Hillf Danton <hdanton@...a.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>,
	Mateusz Guzik <mjguzik@...il.com>,
	"Sapkal, Swapnil" <swapnil.sapkal@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still
 full

On 03/07, Hillf Danton wrote:
>
> On Fri, 7 Mar 2025 11:54:56 +0530 K Prateek Nayak <kprateek.nayak@....com>
> >> step-03
> >> 	task-118766 new reader
> >> 	makes pipe empty
> >
> >Reader seeing a pipe full should wake up a writer allowing 118768 to
> >wakeup again and fill the pipe. Am I missing something?
> >
> Good catch, but that wakeup was cut off [2,3]
>
> [2] https://lore.kernel.org/lkml/20250304123457.GA25281@redhat.com/
> [3] https://lore.kernel.org/all/20250210114039.GA3588@redhat.com/

Why do you think

	[PATCH v2 1/1] pipe: change pipe_write() to never add a zero-sized buffer
	https://lore.kernel.org/all/20250210114039.GA3588@redhat.com/

can make any difference ???

Where do you think a zero-sized buffer with ->len == 0 can come from?

Oleg.