lkml.org 
[lkml]   [2007]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Clear PG_error before reading a page
On Wed, 16 May 2007 17:39:19 +0200 Johann Lombardi <johann@clusterfs.com> wrote:

> On Tue, May 15, 2007 at 02:23:39PM -0700, Andrew Morton wrote:
> > > Yes, indeed. However, as soon as a call to get_block() fails,
> > > do_mpage_readpage() will call block_read_full_page() which will attach
> > > buffers to this page.
> > > Consequently, all subsequent reads will go through block_read_full_page().
> >
> > hm, confused. Why is get_block() failing? That has to go and read
> > metadata.
>
> In fact, I am referring to the first part of my test case (i.e. mount the ext3
> fs, enable medium errors in scsi_debug and try to read a file from the fs).
>
> So, when I try to read a file, ext3_get_block() needs to read metadata from the
> disk. However, given that the SCSI disk simulated by scsi_debug reports medium
> errors, ext3_get_block() returns EIO to the caller (i.e. do_mpage_readpage()).
> That's why get_block() is failing.
>
> Then, do_mpage_readpage() calls block_read_full_page() (via "goto confused").
> block_read_full_page() attaches buffers to this page and calls ext3_get_block()
> which fails for the same reason as before. Consequently, block_read_full_page()
> sets the PG_error flag.
> Moreover, all subsequent readpage calls will go through block_read_full_page()
> because the page has now buffers attached.
>
> 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?

I still worry about the fact that changes in this area could cause the
kernel to do a *lot* more IO attempts against failed devices, or failed
sectors. We already have a few problems in that area.

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?
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-05-16 18:17    [W:0.046 / U:0.408 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site