linux-kernel - Re: [PATCH] Prevent crash on missing sysfs attribute group

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Date:	Tue, 3 Apr 2012 12:16:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Bruno Prémont <bonbons@...ux-vserver.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Prevent crash on missing sysfs attribute group


* Eric W. Biederman <ebiederm@...ssion.com> wrote:

> Ingo Molnar <mingo@...nel.org> writes:
> 
> > * Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >
> >> > Huh, so put repeated, duplicated, inconsistently applied sanity 
> >> > checks into dozens of sysfs attribute using kernel subsystems?
> >>
> >> [...]
> >>
> >> No.  I was not talking about every usage site.
> >
> > Note, I'm not arguing that this isn't a bug in the P4 PMU driver 
> > - it is clearly a bug and I've applied the fix for it. I'm 
> > arguing about the escallation vector that this bug takes - that 
> > is unnecessarily disruptive:
> >
> > You were talking about:
> >
> >> >> FIX perf to include sanity checks.
> >
> > and what the PMU drivers do here is not uncommon at all, and the 
> > bug (for which I applied the fix and will push to Linus ASAP) is 
> > not uncommon either:
> 
> > Bugs happen and indirections happen too. perf uses a generic 
> > PMU driver layer where the lower level layers register 
> > themselves. There's at least a dozen similar constructs in 
> > the kernel and you suggest that the right solution is to put 
> > checks in every one of them, while the nice patch from Bruno 
> > could catch it too, in one central place?
> 
> What is uncommon is that perf_pmu_register is called from an 
> early initcall, and then later a device_init call is used to 
> register the pmu subsystem with sysfs.

This has no relevance to the bug and crash pattern itself 
whatsoever, so stop blathering about unrelated things.

Not filling out a sysfs object attribute is an *easy* driver 
level mistake, I've seen it happen on numerous occasions. Not 
crashing on it in the sysfs layer is an *obvious* debugging 
helper, and I don't understand why you are even arguing about 
this.

Thanks,

	Ingo
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