Re: kern/42455: tstile hang with nfs

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

The following reply was made to PR kern/42455; it has been noted by GNATS.

From: David Holland <dholland-bugs%netbsd.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: kern/42455: tstile hang with nfs
Date: Sun, 2 May 2010 01:44:16 +0000

 On Fri, Apr 30, 2010 at 11:25:02AM +0000, Christoph Egger wrote:
  >  327     2          qemu-dm   netbsd   43 netio        ffffa0000114f3b8
  >  327     1          qemu-dm   netbsd   34 genput       ffffa000005a0840
  >  
  > [...]
  >  This is the hanging 'qemu-dm' process:
  >  
  >  db> tr /a 0xffffa00026628400
  >  trace: pid 327 lid 1 at 0xffffa0002661e880
  >
  > [...]
  >  The question is why does the 'sync' syscall hang in first
  >  place ?
 
 It looks to me as if pid 327 lid 1 is probably waiting for pid 327 lid
 2, which is hanging on the network. It's blocked in genfs_do_putpages
 waiting for the page it's trying to write out to become unbusy, and
 lid 2 there is a clear candidate for holding it.
 
 I don't immediately see how to inspect the uvm structures to find out
 whether this is in fact the case, but maybe someone who knows more
 about uvm can help.
 
 (btw, sorry I never got around to answering your previous mail in this
 PR... it's been marked unread-and-urgent the last three months. sigh)
 
 -- 
 David A. Holland
 dholland%netbsd.org@localhost