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Date:   Fri, 05 Aug 2022 15:05:41 +0530
From:   Siddh Raman Pant <code@siddh.me>
To:     "Eric Biggers" <ebiggers@kernel.org>
Cc:     "christophe.jaillet" <christophe.jaillet@wanadoo.fr>,
        "corbet" <corbet@lwn.net>, "dhowells" <dhowells@redhat.com>,
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        "linux-kernel-mentees" 
        <linux-kernel-mentees@lists.linuxfoundation.org>,
        "linux-kernel" <linux-kernel@vger.kernel.org>,
        "mchehab" <mchehab@kernel.org>, "rdunlap" <rdunlap@infradead.org>
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Subject: Re: [PATCH v2 3/3] kernel/watch_queue: Remove wqueue->defunct and
 use pipe for clear check
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On Fri, 05 Aug 2022 12:54:31 +0530  Eric Biggers  wrote:
> Why is the READ_ONCE() needed?  Doesn't wqueue->lock protect wqueue->pipe?

We are changing the pointer while a notification can be potentially waiting to
be posted to the pipe. So a barrier is needed to prevent compiler magic from
reloading the value.

This was remarked by David Howells here:
https://lore.kernel.org/lkml/3558070.1658933200@warthog.procyon.org.uk/

> This isn't the correct block comment format; it should look like:
> 
>      /*
>       * This pipe will get freed by the caller free_pipe_info().
>       * Removing this reference also prevents new notifications.
>       */
> 
> - Eric
> 

Okay, will make the change.

Thanks,
Siddh