From owner-freebsd-stable  Wed Apr 10 11:54:51 2002
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Date: Wed, 10 Apr 2002 14:54:21 -0400 (EDT)
From: Bruce Campbell <bruce@engmail.uwaterloo.ca>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: Danny Schales <dan@coes.LaTech.edu>,
	Rolandas Naujikas <rolnas@takas.lt>,
	Doug White <dwhite@resnet.uoregon.edu>,
	Wilko Bulte <wkb@freebie.xs4all.nl>,
	Paul Horechuk <phorechuk@docucom.ca>, stable@FreeBSD.ORG,
	jah4007@cs.rit.edu
Subject: Re: nfs_fsync: not dirty  error in 4.5-RELEASE (possible solution)
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After experiencing 9 such panics in a 10 day period, on 3 different
machines, I applied the below possible solution to just one of the 3
systems.  That was 4 days ago.  Since then, none of the 3 systems have
panic'ed ;-(

During the last panics, I was able to determine that the only user
connected was one who was over quota.  He then moved to another of the 3
servers and was the only one connected there, and then that one panic'ed
also.

Despite a number of over quota experiments, I was unable to reproduce
the condition.


On Fri, 29 Mar 2002, Matthew Dillon wrote:
>     Ok, I am putting this back on the main list.
> 
>     After looking at a kernel core that Danny graciously provided, I believe
>     I have located the problem.
> 
>     The core shows NFS panicing on a struct buf showing up on the vnode's 
>     v_dirtyblkhd list that is not marked B_DELWRI.
> 
>     After examining the core I found that the buffer was marked B_INVAL,
>     and I found a case in brelse() where B_DELWRI is cleared on a buffer
>     marked B_DELWRI|B_INVAL without moving it out of the vnode's v_dirtyblkhd
>     list.  Specifically, line 1214 if kern/vfs_bio.c:
> 
>         /*
>          * If B_INVAL, clear B_DELWRI.  We've already placed the buffer
>          * on the correct queue.
>          */
>         if ((bp->b_flags & (B_INVAL|B_DELWRI)) == (B_INVAL|B_DELWRI)) {
>                 bp->b_flags &= ~B_DELWRI;
>                 --numdirtybuffers;
>                 numdirtywakeup(lodirtybuffers);
>         }               
> 
>     I believe that the correct fix is to change this code to:
>     
>         /*
>          * If B_INVAL, clear B_DELWRI.  We've already placed the buffer
>          * on the correct queue.
>          */
>         if ((bp->b_flags & (B_INVAL|B_DELWRI)) == (B_INVAL|B_DELWRI))
> 		bundirty(bp);
> 
>     I would appreciate it if everyone who is able to easily reproduce this
>     panic would test this fix and post your results back to the list.  If
>     this solves the problem I will commit it to -current and -stable.
> 
> 					-Matt
> 					Matthew Dillon 
> 					<dillon@backplane.com>
> 


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