linux-kernel - Re: [PATCH v5 2/2] pipe: use __pipe_{lock,unlock} instead of spinlock

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Date:   Sat, 19 Aug 2023 04:53:03 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Hongchen Zhang <zhanghongchen@...ngson.cn>
Cc:     David Howells <dhowells@...hat.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Steve French <stfrench@...rosoft.com>,
        Jens Axboe <axboe@...nel.dk>, David Disseldorp <ddiss@...e.de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Nick Alcock <nick.alcock@...cle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH v5 2/2] pipe: use __pipe_{lock,unlock} instead of spinlock

On Sat, Aug 19, 2023 at 11:28:58AM +0800, Hongchen Zhang wrote:
> Hi David,
> 
> On 2023/8/14 pm 4:47, David Howells wrote:
> > Hongchen Zhang <zhanghongchen@...ngson.cn> wrote:
> > 
> > > -	spin_lock_irq(&pipe->rd_wait.lock);
> > > +	__pipe_lock(pipe);
> > 
> I changed the code and the post_one_notification is not called inside spin
> lock ,please check this patch again.

In remove_watch_from_object(), you moved post_one_notification() before
lock_queue(), but it's still called inside a RCU read-side critical
section, which cannot sleep.

Please test with CONFIG_DEBUG_ATOMIC_SLEEP before you send a new version.
You should probably turn on DEBUG_SPINLOCK, LOCKDEP, DEBUG_MUTEXES
and a few other debug options.