GIT: unionfs2-2.6.27.y: do_generic_file_read: clear page errors when issuing a fresh read of the page

[Erez Zadok]

commit 9b698b5535523995150a8bebad483d541c5ab9cf
Author: Jeff Moyer <jmoyer at redhat.com>
Date:   Wed May 26 11:49:40 2010 -0400

    do_generic_file_read: clear page errors when issuing a fresh read of the page
    
    commit 91803b499cca2fe558abad709ce83dc896b80950 upstream.
    
    I/O errors can happen due to temporary failures, like multipath
    errors or losing network contact with the iSCSI server. Because
    of that, the VM will retry readpage on the page.
    
    However, do_generic_file_read does not clear PG_error.  This
    causes the system to be unable to actually use the data in the
    page cache page, even if the subsequent readpage completes
    successfully!
    
    The function filemap_fault has had a ClearPageError before
    readpage forever.  This patch simply adds the same to
    do_generic_file_read.
    
    Signed-off-by: Jeff Moyer <jmoyer at redhat.com>
    Signed-off-by: Rik van Riel <riel at redhat.com>
    Acked-by: Larry Woodman <lwoodman at redhat.com>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

diff --git a/mm/filemap.c b/mm/filemap.c
index bff0b00..a4800c5 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1118,6 +1118,12 @@ page_not_up_to_date_locked:
 		}
 
 readpage:
+		/*
+		 * A previous I/O error may have been due to temporary
+		 * failures, eg. multipath errors.
+		 * PG_error will be set again if readpage fails.
+		 */
+		ClearPageError(page);
 		/* Start the actual read. The read will unlock the page. */
 		error = mapping->a_ops->readpage(filp, page);