linux-kernel - Re: [PATCH] vsprintf: Do not break early boot with probing addresses

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Date:   Tue, 14 May 2019 15:35:03 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     David Laight <David.Laight@...lab.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        christophe leroy <christophe.leroy@....fr>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        "Tobin C . Harding" <me@...in.cc>, Michal Hocko <mhocko@...e.cz>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Russell Currey <ruscur@...sell.cc>,
        Stephen Rothwell <sfr@...abs.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing
 addresses

On Tue, 14 May 2019 21:13:06 +0200
Geert Uytterhoeven <geert@...ux-m68k.org> wrote:

> > > Do we care about the value? "(-E%u)"?  
> >
> > That too could be confusing. What would (-E22) be considered by a user
> > doing an sprintf() on some string. I know that would confuse me, or I
> > would think that it was what the %pX displayed, and wonder why it
> > displayed it that way. Whereas "(fault)" is quite obvious for any %p
> > use case.  
> 
> I would immediately understand there's a missing IS_ERR() check in a
> function that can return  -EINVAL, without having to add a new printk()
> to find out what kind of bogus value has been received, and without
> having to reboot, and trying to reproduce...

Hi Geert,

I have to ask. Has there actually been a case that you used a %pX and
it faulted, and you had to go back to find what the value of the
failure was?

IMO, sprintf() should not be a tool to do this, because then people
will not add their IS_ERR() and just let sprintf() do the job for them.
I don't think that would be wise to allow.

-- Steve