linux-kernel - Re: [PATCH 1/3] dcache: add a new enum type for 'dentry_d_lock

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Message-ID: <20191115085805.008870cb@gandalf.local.home>
Date:   Fri, 15 Nov 2019 08:58:05 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Greg KH <gregkh@...uxfoundation.org>, yu kuai <yukuai3@...wei.com>,
        rafael@...nel.org, oleg@...hat.com, mchehab+samsung@...nel.org,
        corbet@....net, tytso@....edu, jmorris@...ei.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        zhengbin13@...wei.com, yi.zhang@...wei.com,
        chenxiang66@...ilicon.com, xiexiuqi@...wei.com
Subject: Re: [PATCH 1/3] dcache: add a new enum type for
 'dentry_d_lock_class'

On Fri, 15 Nov 2019 13:48:23 +0000
Al Viro <viro@...iv.linux.org.uk> wrote:

> > BTW, what do you mean by "can debugfs_remove_recursive() rely upon the
> > lack of attempts to create new entries inside the subtree it's trying
> > to kill?"  
> 
> Is it possible for something to call e.g. debugfs_create_dir() (or any
> similar primitive) with parent inside the subtree that has been
> passed to debugfs_remove_recursive() call that is still in progress?
> 
> If debugfs needs to cope with that, debugfs_remove_recursive() needs
> considerably heavier locking, to start with.

I don't know about debugfs, but at least tracefs (which cut and pasted
from debugfs) does not allow that. At least in theory it doesn't allow
that (and if it does, it's a bug in the locking at the higher levels).

And perhaps debugfs shouldn't allow that either. As it is only suppose
to be a light weight way to interact with the kernel, hence the name
"debugfs".

Yu, do you have a test case for the "infinite loop" case?

-- Steve