linux-kernel - Re: [PATCH 00/16 v3] tracing: Add new file system tracefs

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Message-ID: <20150127101953.3245aaed@gandalf.local.home>
Date:	Tue, 27 Jan 2015 10:19:53 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 00/16 v3] tracing: Add new file system tracefs

On Tue, 27 Jan 2015 04:38:39 +0000
Al Viro <viro@...IV.linux.org.uk> wrote:

> On Mon, Jan 26, 2015 at 08:03:50PM -0500, Steven Rostedt wrote:
> > On Mon, 26 Jan 2015 20:02:18 -0500
> > Steven Rostedt <rostedt@...dmis.org> wrote:
> > 
> > 
> > > Now you see why I found just dropping the parent mutex easier.
> > 
> > And this is probably why kernfs does things the way it does. I can
> > imagine it having the same locking issues.
> 
> The least said about kernfs locking, the better...
> 
> As for the use of trace_types_lock to serialize rmdir vs. event
> addition/removal, I wonder what's wrong with actually using the
> ->i_mutex of /instances - you have a reference to its dentry,
> after all...

You mean, instead of grabbing trace_types_lock for modifying of events
and trace arrays, we should grab the dentry->d_inode->i_mutex?

BTW, what exactly can go wrong with the current method I have that
releases the i_mutex, calls the mkdir() method, and then regrabs the
i_mutex?

-- Steve
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