Subject: Re: Re: [PATCH v4] pipe: use __pipe_{lock,unlock} instead of spinlock
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>
References: <20230129060452.7380-1-zhanghongchen@loongson.cn>
 <CAHk-=wjw-rrT59k6VdeLu4qUarQOzicsZPFGAO5J8TKM=oukUw@mail.gmail.com>
From:   Hongchen Zhang <zhanghongchen@loongson.cn>
Message-ID: <3abdd2bf-49ba-6c85-3ff6-29915eb40ac4@loongson.cn>
Date:   Fri, 3 Feb 2023 10:24:58 +0800
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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