linux-kernel - [ 102/110] rbd: fix I/O error propagation for reads

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Message-Id: <20130925001334.468551389@linuxfoundation.org>
Date:	Tue, 24 Sep 2013 17:15:40 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Josh Durgin <josh.durgin@...tank.com>,
	Alex Elder <alex.elder@...aro.org>
Subject: [ 102/110] rbd: fix I/O error propagation for reads

3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josh Durgin <josh.durgin@...tank.com>

commit 17c1cc1d9293a568a00545469078e29555cc7f39 upstream.

When a request returns an error, the driver needs to report the entire
extent of the request as completed.  Writes already did this, since
they always set xferred = length, but reads were skipping that step if
an error other than -ENOENT occurred.  Instead, rbd would end up
passing 0 xferred to blk_end_request(), which would always report
needing more data.  This resulted in an assert failing when more data
was required by the block layer, but all the object requests were
done:

[ 1868.719077] rbd: obj_request read result -108 xferred 0
[ 1868.719077]
[ 1868.719518] end_request: I/O error, dev rbd1, sector 0
[ 1868.719739]
[ 1868.719739] Assertion failure in rbd_img_obj_callback() at line 1736:
[ 1868.719739]
[ 1868.719739]   rbd_assert(more ^ (which == img_request->obj_request_count));

Without this assert, reads that hit errors would hang forever, since
the block layer considered them incomplete.

Fixes: http://tracker.ceph.com/issues/5647
Signed-off-by: Josh Durgin <josh.durgin@...tank.com>
Reviewed-by: Alex Elder <alex.elder@...aro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/rbd.c |   14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1565,11 +1565,12 @@ rbd_img_obj_request_read_callback(struct
 		obj_request, obj_request->img_request, obj_request->result,
 		xferred, length);
 	/*
-	 * ENOENT means a hole in the image.  We zero-fill the
-	 * entire length of the request.  A short read also implies
-	 * zero-fill to the end of the request.  Either way we
-	 * update the xferred count to indicate the whole request
-	 * was satisfied.
+	 * ENOENT means a hole in the image.  We zero-fill the entire
+	 * length of the request.  A short read also implies zero-fill
+	 * to the end of the request.  An error requires the whole
+	 * length of the request to be reported finished with an error
+	 * to the block layer.  In each case we update the xferred
+	 * count to indicate the whole request was satisfied.
 	 */
 	rbd_assert(obj_request->type != OBJ_REQUEST_NODATA);
 	if (obj_request->result == -ENOENT) {
@@ -1578,14 +1579,13 @@ rbd_img_obj_request_read_callback(struct
 		else
 			zero_pages(obj_request->pages, 0, length);
 		obj_request->result = 0;
-		obj_request->xferred = length;
 	} else if (xferred < length && !obj_request->result) {
 		if (obj_request->type == OBJ_REQUEST_BIO)
 			zero_bio_chain(obj_request->bio_list, xferred);
 		else
 			zero_pages(obj_request->pages, xferred, length);
-		obj_request->xferred = length;
 	}
+	obj_request->xferred = length;
 	obj_request_done_set(obj_request);
 }
 


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