linux-kernel - Re: [PATCH 1/4] fs/pipe: Convert to lockdep_cmp

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Message-ID: <CA+icZUXdhRY-wRZCFWJA4ppz98Shjft_W9xDnvAHe0AZKH7zvA@mail.gmail.com>
Date: Mon, 5 Feb 2024 10:59:47 +0100
From: Sedat Dilek <sedat.dilek@...il.com>
To: Jan Kara <jack@...e.cz>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>, linux-kernel@...r.kernel.org, 
	netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org, peterz@...radead.org, 
	boqun.feng@...il.com, Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH 1/4] fs/pipe: Convert to lockdep_cmp_fn

On Mon, Feb 5, 2024 at 10:54 AM Jan Kara <jack@...e.cz> wrote:
>
> On Fri 02-02-24 13:25:20, Sedat Dilek wrote:
> > On Fri, Feb 2, 2024 at 1:12 PM Jan Kara <jack@...e.cz> wrote:
> > >
> > > On Fri 26-01-24 21:08:28, Kent Overstreet wrote:
> > > > *_lock_nested() is fundamentally broken; lockdep needs to check lock
> > > > ordering, but we cannot device a total ordering on an unbounded number
> > > > of elements with only a few subclasses.
> > > >
> > > > the replacement is to define lock ordering with a proper comparison
> > > > function.
> > > >
> > > > fs/pipe.c was already doing everything correctly otherwise, nothing
> > > > much changes here.
> > > >
> > > > Cc: Alexander Viro <viro@...iv.linux.org.uk>
> > > > Cc: Christian Brauner <brauner@...nel.org>
> > > > Cc: Jan Kara <jack@...e.cz>
> > > > Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
> > >
> > > I had to digest for a while what this new lockdep lock ordering feature is
> > > about. I have one pending question - what is the motivation of this
> > > conversion of pipe code? AFAIU we don't have any problems with lockdep
> > > annotations on pipe->mutex because there are always only two subclasses?
> > >
> > >                                                                 Honza
> >
> > Hi,
> >
> > "Numbers talk - Bullshit walks." (Linus Torvalds)
> >
> > In things of pipes - I normally benchmark like this (example):
> >
> > root# cat /dev/sdc | pipebench > /dev/null
> >
> > Do you have numbers for your patch-series?
>
> Sedat AFAIU this patch is not about performance at all but rather about
> lockdep instrumentation... But maybe I'm missing your point?
>

Sorry, I missed the point, Jan.

-Sedat-