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    SubjectRe: Clear PG_error before reading a page
    On Wed, 16 May 2007 17:39:19 +0200 Johann Lombardi <> 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?
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