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Date: Tue, 7 Nov 2017 17:44:13 -0500
From: Steven Rostedt <>
To: Linus Torvalds <>
Cc: Kees Cook <>, "Tobin C. Harding" <>,
 "Paul E. McKenney" <>, Andy Lutomirski
 <>, Joe Perches <>, Network Development
 <>, David Miller <>,
 <>, "Jason A. Donenfeld"
 <>, "Theodore Ts'o" <>, Paolo Bonzini
 <>, Tycho Andersen <>, "Roberts, William
 C" <>, Tejun Heo <>, Jordan Glover
 <>, Greg KH <>, Petr
 Mladek <>, Ian Campbell <>, Sergey
 Senozhatsky <>, Catalin Marinas
 <>, Will Deacon <>, Chris Fries
 <>, Dave Weinstein <>, Daniel Micay
 <>, Djalal Harouni <>, Linux Kernel
 Mailing List <>, Peter Zijlstra
Subject: Re: [PATCH v3] scripts: add

On Tue, 7 Nov 2017 13:44:01 -0800
Linus Torvalds <> wrote:

> > Looking other places that stand out, it seems like
> > /proc/lockdep_chains and /proc/lockdep (CONFIG_LOCKDEP=y) has a ton of
> > %p usage. It's unclear to me if a hash is sufficient for meaningful
> > debugging there?  
> Maybe not, but that is also _so_ esoteric that I suspect the right fix
> is to just make it root-only readable.

Also note, I don't believe anyone should be running a LOCKDEP
configured kernel in a production (secured) environment. As it adds
quite a bit of overhead. It's something you run on test environments to
make sure it doesn't detect any possible deadlocks.

> I've never used it, we should check with people who have. I get the
> feeling that this is purely for PeterZ debugging.

I've used it. But then again, I also debug lockdep ;-)

> The very first commit that introduced that code actually has a
>     (FIXME: should go into debugfs)
> so I suspect it never should have been user-readable to begin with. I
> guess it makes some things easier, but it really is *very* different
> from things like profiling.

Want me to whip up a patch to move the file?

-- Steve

> Profiling you often *cannot* do as root - some things you profile
> really shouldn't be run as root, and might even refuse to do so. So
> requiring you to be root just to get a kernel profile is very bad.
> But looking at lockdep stats? Yeah, 'sudo' isn't so big of a deal.

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