Subject: Re: ffs_alloccg panic
To: Mike Long <>
From: Michael L. VanLoon -- <>
List: current-users
Date: 07/22/1996 09:07:31
>>But, this raises a question: do panics in the kernel, with DIAGNOSTIC
>>turned on, still signal a potential bug?  I'm thinking kind of
>>anologeous to warnings emitted from a C compiler.  In other words: in
>>a kernel where all known "warnings" were "fixed", should it be
>>expected that this kernel would never panic if DIAGNOSTIC was built

>Mostly; unrecoverable errors would still cause a panic.

Right, but I'm getting panics with DIAGNOSTIC built in that don't
occur with it off.  Either someone is making a wrong assumption in
some diagnostic code, or there is a silent bug eating its way through
my (and maybe all of our) system(s).

>Code wrapped by #ifdef DIAGNOSTIC performs sanity checking of
>assumptions made by kernel code.  In your case, disabling DIAGNOSTIC
>may eliminate panics, but at the cost of possibly introducing silent
>filesystem corruption.  I'd prefer a panic, myself.

Well, I'd prefer to not have my system hang every couple of days.  I'd
prefer a panic iff the bug could be diagnosed and fixed quickly
afterwards.  Unfortunately, my mail went completely unanswered, and I
don't have the expertise to fix it.  Maybe I'll resubmit my mail as a
PR, but I don't know that I have enough info to make it a useful PR.

Anyway, I'd also prefer it not to panic if this is an incorrect
assumption in the diagnostic code.

But the gist of this is you confirming what I thought.  That, with a
system known to be free of all "known" "bugs", enabling DIAGNOSTIC
should not cause any panics.  (This an in theory, not necessarily in
practice, kind of thing.)

  Michael L. VanLoon                       
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