linux-kernel - Re: [PATCH] kernel/watch_queue: Make pipe NULL while clearing watch

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Message-ID: <1822b768504.1d4e377e236061.5518350412857967240@siddh.me>
Date:   Sat, 23 Jul 2022 19:59:23 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     "Greg KH" <gregkh@...uxfoundation.org>
Cc:     "David Howells" <dhowells@...hat.com>,
        "Christophe JAILLET" <christophe.jaillet@...adoo.fr>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        "linux-security-modules" <linux-security-module@...r.kernel.org>,
        "linux-kernel-mentees" 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "syzbot+c70d87ac1d001f29a058" 
        <syzbot+c70d87ac1d001f29a058@...kaller.appspotmail.com>
Subject: Re: [PATCH] kernel/watch_queue: Make pipe NULL while clearing
 watch_queue

On Sat, 23 Jul 2022 19:34:17 +0530  Greg KH <gregkh@...uxfoundation.org> wrote:
> Also you now have a spinlock held when calling rcu_read_unlock(), are
> you sure that's ok?
> 
> 

We logically should not do write operations in a read critical section, so the
nulling of `wqueue->pipe->watch_queue` should happen after rcu_read_unlock().
Also, since we already have a spinlock, we can use it to ensure the nulling.
So I think it is okay.

Though, it is my first time encountering a spinlock and an rcu lock together,
so if I am wrong, please do correct me.

Thanks,
Siddh