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Date: Tue, 14 May 2019 15:35:03 -0400
From: Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing
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To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: David Laight <David.Laight@aculab.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Petr Mladek <pmladek@suse.com>, Andy Shevchenko <andriy.shevchenko@linux.intel.com>, christophe leroy <christophe.leroy@c-s.fr>, Linus Torvalds <torvalds@linux-foundation.org>, Rasmus Villemoes <linux@rasmusvillemoes.dk>, "Tobin C . Harding" <me@tobin.cc>, Michal Hocko <mhocko@suse.cz>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>, Russell Currey <ruscur@russell.cc>, Stephen Rothwell <sfr@ozlabs.org>, Heiko Carstens <heiko.carstens@de.ibm.com>, "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>, "linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>
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On Tue, 14 May 2019 21:13:06 +0200
Geert Uytterhoeven <geert@linux-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