Re: bin/27179 (dump(8) goes into loop, never finishing dump)

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

The following reply was made to PR bin/27179; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: bin/27179 (dump(8) goes into loop, never finishing dump)
Date: Mon, 3 May 2010 02:46:31 +0000

 On Mon, May 03, 2010 at 01:26:40AM +0000, dholland%NetBSD.org@localhost wrote:
  > I see nothing in the changelogs for dump that would have been remotely
  > likely to correct this. All the same, it would be extremely useful to
  > know if this problem has been seen recently.
 
 Looking into it some more I have the following observations:
 
 (1) it is probably a race condition somewhere, so there's some more or
 less fixed probability of triggering it at any given moment, which is
 why it manifests mostly on large dumps;
 
 (2) in the case cited, it is making progress, or thinks it is, just at
 about 1/100th the normal rate;
 
 (3) the scheme dump uses to coordinate its subprocesses is fragile and
 could be messed up by all manner of kernel bugs, particularly in
 signals or AF_UNIX sockets; however, I also can't so far rule out a
 corner case in the state transitions;
 
 (4) however, all of the likely issues I can think of (of either kind)
 would lead to it hanging completely, not proceeding at a crawl.
 
 (5) I also have no idea why it would be correlated with using amanda.
 
 
 So I dunno. If anyone manages to reproduce this it would be useful to
 know where the various dump processes are spending their time while
 mostly not making progress...
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost