Re: Re: [PATCH v4] pipe: use __pipe_{lock,unlock} instead of spinlock

From: Hongchen Zhang <zhanghongchen@loongson.cn>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	"Christian Brauner (Microsoft)" <brauner@kernel.org>,
	Luis Chamberlain <mcgrof@kernel.org>,
	David Howells <dhowells@redhat.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	"Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
	Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	maobibo <maobibo@loongson.cn>,
	Matthew Wilcox <willy@infradead.org>,
	Sedat Dilek <sedat.dilek@gmail.com>
Subject: Re: Re: [PATCH v4] pipe: use __pipe_{lock,unlock} instead of spinlock
Date: Fri, 3 Feb 2023 10:24:58 +0800	[thread overview]
Message-ID: <3abdd2bf-49ba-6c85-3ff6-29915eb40ac4@loongson.cn> (raw)
In-Reply-To: <CAHk-=wjw-rrT59k6VdeLu4qUarQOzicsZPFGAO5J8TKM=oukUw@mail.gmail.com>

Hi Linus,

On 2023/1/29 下午3:33, Linus Torvalds wrote:
> On Sat, Jan 28, 2023 at 10:05 PM Hongchen Zhang
> <zhanghongchen@loongson.cn> wrote:
>>
>> Use spinlock in pipe_{read,write} cost too much time,IMO
>> pipe->{head,tail} can be protected by __pipe_{lock,unlock}.
>> On the other hand, we can use __pipe_{lock,unlock} to protect
>> the pipe->{head,tail} in pipe_resize_ring and
>> post_one_notification.
> 
> No, we really can't.
> 
> post_one_notification() is called under the RCU lock held, *and* with
> a spinlock held.
> 
> It simply cannot do a sleeping lock like __pipe_lock().
> 
> So that patch is simply fundamentally buggy, I'm afraid.
> 
>                  Linus
> 
Thanks for your review,Let me find out if there is any way to solve the
problem you said.

Best Regards
Hongchen Zhang