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

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Message-ID: <b8f0fc4c-7b54-4bec-b3cf-9e0b542832f4@amd.com>
Date: Wed, 26 Feb 2025 23:26:35 +0530
From: "Sapkal, Swapnil" <swapnil.sapkal@....com>
To: Oleg Nesterov <oleg@...hat.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>, <mjguzik@...il.com>
Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still
 full

Hi Oleg,

On 2/26/2025 5:08 PM, Oleg Nesterov wrote:
> Thanks Sapkal!
> 
> I'll try to think. Meanwhile,
> 
> On 02/26, Sapkal, Swapnil wrote:
>>
>> Exact command with parameters is
>>
>> 	/usr/bin/hackbench -g 16 -f 20 --threads --pipe -l 100000 -s 100
> 
> Can you reproduce with "--process" rather than "--threads" ?
> 
I was able to reproduce the issue with processes also. Total 33 
processes were sleeping out of which 20 were readers and 13 were writers.

The stack trace for main hackbench process is as follows:

[<0>] do_wait+0xb5/0x110
[<0>] kernel_wait4+0xb2/0x150
[<0>] __do_sys_wait4+0x89/0xa0
[<0>] __x64_sys_wait4+0x20/0x30
[<0>] x64_sys_call+0x1bf7/0x2140
[<0>] do_syscall_64+0x6f/0x110
[<0>] entry_SYSCALL_64_after_hwframe+0x76/0x7e

I am trying to reproduce the issue with suggestions by Mateusz.

> Oleg.
> 
--
Thanks and Regards,
Swapnil