Re: A unresponsive file system can hang all I/O in the system onlinux-2.6.23-rc6 (dirty_thresh problem?)

From: Andrew Morton
Date: Fri Sep 28 2007 - 14:05:13 EST

On Fri, 28 Sep 2007 07:28:52 -0600 corbet@xxxxxxx (Jonathan Corbet) wrote:

> Andrew wrote:
> > It's unrelated to the actual value of dirty_thresh: if the machine fills up
> > with dirty (or unstable) NFS pages then eventually new writers will block
> > until that condition clears.
> >
> > 2.4 doesn't have this problem at low levels of dirty data because 2.4
> > VFS/MM doesn't account for NFS pages at all.
> Is it really NFS-related? I was trying to back up my 2.6.23-rc8 system
> to an external USB drive the other day when something flaked and the
> drive fell off the bus. That, too, was sufficient to wedge the entire
> system, even though the only thing which needed the dead drive was one
> rsync process. It's kind of a bummer to have to hit the reset button
> after the failure of (what should be) a non-critical piece of hardware.
> Not that I have a fix to propose...:)

That's a USB bug, surely. What should happen is that the kernel attempts
writeback, gets an IO error and then your data gets lost.

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