Re: kern/47815: Reader / writer lock error: rw_vector_enter: locking against myself

[David Holland <dholland-bugs%netbsd.org@localhost>]

The following reply was made to PR kern/47815; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/47815: Reader / writer lock error: rw_vector_enter: locking
 against myself
Date: Mon, 7 Oct 2013 02:26:32 +0000

 On Sat, May 18, 2013 at 11:30:08PM +0000, Emil ?berg wrote:
  > Care to explain how a dirty '/' can cause kernel panic like that?
  > Just out of curiosity.
 
 There are a lot of ways. For example, the kernel is dependent on the
 filesystem being a tree in order to maintain a fixed locking order.
 (Usually top-down, but there have been implementations that work
 bottom-up.)
 
 Then if you have a corrupted filesystem with a crosslinked directory,
 and the references to it aren't at the same depth, to avoid deadlock
 you have to lock it both before and after anything of a depth in
 between, and that's obviously impossible.
 
 In this case it looks less exotic than that -- given the panic and the
 context probably there was a directory with an entry (other than .)
 that pointed to itself.
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost