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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250102164617.GB30778@redhat.com>
Date: Thu, 2 Jan 2025 17:46:18 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: WangYuli <wangyuli@...ontech.com>
Cc: Manfred Spraul <manfred@...orfullife.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christian Brauner <brauner@...nel.org>,
	David Howells <dhowells@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, yushengjin@...ontech.com,
	zhangdandan@...ontech.com, chenyichong@...ontech.com
Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still
 full

On 01/03, WangYuli wrote:
>
> [Adding some of my colleagues who were part of the original submission to
> the CC list for their information.]

OK,

> perhaps we should include a link to the original discussion
>
> Link: https://lore.kernel.org/all/75B06EE0B67747ED+20241225094202.597305-1-wangyuli@uniontech.com/
...
> Reported-by: WangYuli <wangyuli@...ontech.com>

WangYuli, this patch has nothing to do with your original patch and
the discussion above.

> I'm happy to provide more test results for this patch if it's not too late.

Would be great, but I don't think this patch can make any difference
performance-wise in practice. Short reads are not that common, I guess.

> Hmm..
> Initially, the sole purpose of our original patch was to simply check if
> there were any waiting processes in the process wait queue to avoid
> unnecessary wake-ups, for both reads and writes.

Exactly. So once again, this patch is orthogonal to the possible
wq_has_sleeper() optimizations.

> Do you have any suggestions on how we could better
> achieve our original objective?

See
	wakeup_pipe_readers/writers() && pipe_poll()
	https://lore.kernel.org/all/20250102163320.GA17691@redhat.com/

Oleg.