linux-kernel - Re: [RFC] fsnotify: allow sleepable child dentry flag update

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Message-ID: <Y0ikfeqm0ASZTR0g@ZenIV>
Date:   Fri, 14 Oct 2022 00:51:25 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Stephen Brennan <stephen.s.brennan@...cle.com>
Cc:     Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] fsnotify: allow sleepable child dentry flag update

On Thu, Oct 13, 2022 at 03:27:19PM -0700, Stephen Brennan wrote:

> So I have two more narrowly scoped strategies to improve the situation. Both are
> included in the hacky, awful patch below.
> 
> First, is to let __fsnotify_update_child_dentry_flags() sleep. This means nobody
> is holding the spinlock for several seconds at a time. We can actually achieve
> this via a cursor, the same way that simple_readdir() is implemented. I think
> this might require moving the declaration of d_alloc_cursor() and maybe
> exporting it. I had to #include fs/internal.h which is not ok.

Er...  Won't that expose every filesystem to having to deal with cursors?
Currently it's entirely up to the filesystem in question and I wouldn't
be a dime on everyone being ready to cope with such surprises...