linux-kernel - Re: [PATCH] taging: speakup: remove volatile

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Date:   Fri, 22 May 2020 19:13:12 +0200
From:   Samuel Thibault <samuel.thibault@...-lyon.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Dan Carpenter <dan.carpenter@...cle.com>,
        MugilRaj <dmugil2000@...il.com>, devel@...verdev.osuosl.org,
        Kirk Reiser <kirk@...sers.ca>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        speakup@...ux-speakup.org, linux-kernel@...r.kernel.org,
        Chris Brannon <chris@...-brannons.com>
Subject: Re: [PATCH] taging: speakup: remove volatile

Joe Perches, le ven. 22 mai 2020 09:36:05 -0700, a ecrit:
> On Fri, 2020-05-22 at 13:34 +0300, Dan Carpenter wrote:
> > On Fri, May 22, 2020 at 02:46:28PM +0530, MugilRaj wrote:
> > > fix checkpatch.pl warning, which is Use of volatile is usually wrong: see
> > > Documentation/process/volatile-considered-harmful.rst
> > > Signed-off-by: MugilRaj <dmugil2000@...il.com>
> > 
> > Please put a blank before the Signed-off-by line.
> > 
> > Probably there should be a space between your first and last name.  It's
> > supposed to your legal name like for signing a legal document so use
> > whatever is appropriate legal documents in your country.
> > 
> > Also the Documentation/process/volatile-considered-harmful.rst explains
> > that people often use "volatile" when they should be using locking for
> > synchronization.  That seems to be the case here.  So the correct fix is
> > to add locking.  That's a little bit complicated to do and requires
> > testing.
> > 
> > If we apply this patch, then we have silenced the warning so now someone
> > will have to look for the bug.  But if we leave it as-is, then everyone
> > will know that the code is buggy.  So let's leave it as-is until we are
> > able to fix the bug.
> > 
> > It's always better to have easy to find bugs, than hidden bugs.
> 
> And better still to comment known opportunities to
> improve the code so the next time someone tries to
> remove this volatile, there's a comment right there
> showing what's necessary instead.

Actually I don't think adding the suggestion is a good thing if it's
only a "rule-of-thumb-replace-volatile-with-lock".

Actually possibly volatile might not even be needed because there could
be already a lock protecting this.

Put another way: I don't think putting any hint here would help, on the
contrary, somebody has to really look at what protection is needed,
without getting influenced by rules-of-thumb.

Samuel