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Re: Ext2 superblock fault

From: Samuel Thibault
Subject: Re: Ext2 superblock fault
Date: Mon, 10 Mar 2008 10:49:21 +0000
User-agent: Mutt/1.5.12-2006-07-14

Thomas Bushnell BSG, le Sun 09 Mar 2008 22:17:05 -0400, a écrit :
> On Mon, 2008-03-10 at 01:19 +0000, Samuel Thibault wrote:
> > This thread is syncing everything, i.e. asking a lot of writes, which
> > triggers the creation of a lot of threads.  Unfortunately the superblock
> > was paged out, so they all block on reading it.  Unfortunately, since in
> > Debian there is a patch which limits the number of created threads,
> > the read of the superblock doesn't actually create a new thread, that is
> > delayed.  But since none of the existing threads can progress (since
> > they are all waiting for the super block), things are just dead
> > locked...
> As a general rule, the Hurd always assumes that an RPC can be handled;
> this is quite emebedded in the way diskfs works.
> A patch which limits the number of threads is inherently buggy in the
> Hurd, and that patch MUST be disabled for anything to work properly.

Well, there is still a limit in the number of threads in the kernel
itself: THREAD_MAX...

Yes, that should too be dynamically expandable...

> > I'm currently using a quite ugly patch (on top of the >2GB patch) to 
> > avoid this by just always keeping a copy of the superblock, attached. 
> > I'll commit it in the Debian package.
> This is not a fix.  This just postpones the problem.

It makes it much less frequent, which is good for the Debian buildd for


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