Re: Clear PG_error before reading a page

[Johann Lombardi <johann@clusterfs.com>]

On Wed, May 16, 2007 at 09:12:17AM -0700, Andrew Morton wrote:
> > Basically, my problem is that afterwards, when the device no longer returns
> > any errors, the PG_error flag is never cleared and, as a result, I keep
> > getting -EIO. That's the problem I'd like to address.
> > 
> 
> hm, OK.  So, where are we up to?

Once the errors reported by the underlying device are corrected, we must
unmount/remount the filesystem if we want to use it.
In fact, since readahead ignores I/O errors, the pagecache is populated
with pages having the PG_error flag set and buffers attached.
Since PG_error is then never cleared, we keep getting EIO despite that
the underlying device works just fine.

> What is the actual real-world operational scenario here?  Would it be a
> hotplugged disk?  A transient network failure in a SAN?  IOW, is it
> something from which the kernel should automatically recover, or it is a
> situation in which manual intervention would be better?

The real-world operational scenario is a storage system reporting medium
errors which can be corrected by a manual intervention.

Johann