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

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Message-ID: <20250225115736.GA18523@redhat.com>
Date: Tue, 25 Feb 2025 12:57:37 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: "Sapkal, Swapnil" <swapnil.sapkal@....com>
Cc: Manfred Spraul <manfred@...orfullife.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Christian Brauner <brauner@...nel.org>,
	David Howells <dhowells@...hat.com>,
	WangYuli <wangyuli@...ontech.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	K Prateek Nayak <kprateek.nayak@....com>,
	"Shenoy, Gautham Ranjal" <gautham.shenoy@....com>,
	Neeraj.Upadhyay@....com
Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still
 full

On 02/24, Oleg Nesterov wrote:
>
> Just in case, did you use
>
> 	https://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git/tree/src/hackbench/hackbench.c
>
> ?

Or did you use another version?

Exactly what parameters did you use?

If possible, please reproduce the hang again. How many threads/processes
sleeping in pipe_read() or pipe_write() do you see? (you can look at
/proc/$pid/stack).

Please pick one sleeping writer, and do

	$ strace -p pidof_that_write

this should wake this writer up. If a missed wakeup is the only problem,
hackbench should continue.

The more info you can provide the better ;)

Oleg.