linux-kernel - Re: [PATCH 2/4] panic: Allow taint flag for warnings to be changed from TAINT

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Date:	Tue, 23 Mar 2010 13:23:00 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	David Woodhouse <dwmw2@...radead.org>,
	linux-pci@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-parisc@...r.kernel.org, linuxppc-dev@...abs.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org
Subject: Re: [PATCH 2/4] panic: Allow taint flag for warnings to be changed
 from TAINT_WARN

On Tue, 2010-03-23 at 16:45 +0900, Paul Mundt wrote:
> On Sat, Mar 20, 2010 at 11:05:40PM +0000, Ben Hutchings wrote:
> > WARN() is used in some places to report firmware or hardware bugs that
> > are then worked-around.  These bugs do not affect the stability of the
> > kernel and should not set the usual TAINT_WARN flag.  To allow for
> > this, add WARN_TAINT() and WARN_TAINT_ONCE() macros that take a taint
> > flag as argument.
> > 
> > Architectures that implement warnings using trap instructions instead
> > of calls to warn_slowpath_*() must now implement __WARN_TAINT(taint)
> > instead of __WARN().
> > 
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> > The architecture-specific changes here are untested and need to be
> > reviewed by architecture maintainers.
> > 
> I'm a bit confused about how this is supposed to work, the TAINT_xxx
> values are bit positions presently from 0 to 10, while BUGFLAG_xxx are
> ranged from 0 up. You've set up BUGFLAG_TAINT() to that the TAINT_xxx
> value is shifted up 8 bits but neglected the fact that the trap type is
> 16-bits on most (all?) of the platforms using trap-based BUG handling.
> 
> If the 'taint' in question is just the TAINT_xxx value by itself and will
> never be a bitmap then that's fine, but there's certainly not enough room
> to pass the bitmap in on top of the bugflag otherwise (I don't know if
> this is your intention or not though).

Yes, the taint value must be a bit number not a flag.  Sloppy wording on
my part.

> Also note that some platforms (like SH) implement additional bugflags, so
> we at least want to keep the lower byte available for architecture
> private use.

I noticed, that's why I started at 8 not 1.

> Having said that, the current patch does work for me, although I'm a bit
> nervous about someone thinking it's ok to pass in a taint bitmap here.

We can maybe use BUILD_BUG_ON() here as the taint bit is already
required to be a compile-time constant.

Ben.

> Tested-by: Paul Mundt <lethal@...ux-sh.org>
> 

-- 
Ben Hutchings
Any smoothly functioning technology is indistinguishable from a rigged demo.

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