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Date:      Mon, 9 Mar 1998 23:38:34 +0100
From:      Ollivier Robert <roberto@keltia.freenix.fr>
To:        current@FreeBSD.ORG
Subject:   Re: page fault while in kernel mode (-current from this morning && softupdates)
Message-ID:  <19980309233834.A297@keltia.freenix.fr>
In-Reply-To: <13409.889399148@critter.freebsd.dk>; from Poul-Henning Kamp on Mon, Mar 09, 1998 at 12:19:08AM %2B0100
References:  <19980308230222.A9458@keltia.freenix.fr> <13409.889399148@critter.freebsd.dk>

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According to Poul-Henning Kamp:
> Considering that it mentions "allocindir" it would be obvious that it
> involves files bigger than what we have in our source-tree.  That
> should also be the avenue to reproduction I think...

Reproducting it is very easy :-)

Finding the cause is not. One of the problem I have is that I can work only 
a kernel core dump, being unable to do remote debugging. The trace I get
shows it stopped in _softdep_setup_allocindir_page when the real point of
failure is the bcopy at the end of setup_allocindir_phase2.

I don't have access to the latter's variables since it is a private
function (I guess). I'll make it a public one and see if I can dig
something out of this.

Either one of the two pointers (newindirdep->ir_saveddata,
newindirdep->ir_savebp->b_data) is bad or bp->b_bcount is too big (8192
which seems right for an indirect block on a 8k/1k FS).

Just extending an existing file doen't seem to trigger it (just tried it).
Using DDB and putting a break point in setup_allocindir_phrase2 shows that
the function is called many times but I can't get the bug to manifest
inside DDB <sigh>.

I'd appreciate if someone with more internal knowledge than I have could
help :-)

> >It happens for me in two cases:
> >- rnews batch processing,
> >- procmail delivering mail into mailboxes.

I can see why for the latter case (procmail tries to append a message in
one mailbox). The former could be .overview or history append...
-- 
Ollivier ROBERT -=- FreeBSD: The Power to Serve! -=- roberto@keltia.freenix.fr
FreeBSD keltia.freenix.fr 3.0-CURRENT #0: Sun Mar  1 18:50:39 CET 1998

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