[3.16.y-ckt stable] Patch "xen/blkback: unmap all persistent grants when frontend gets disconnected" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Mon Nov 17 11:16:49 UTC 2014


This is a note to let you know that I have just added a patch titled

    xen/blkback: unmap all persistent grants when frontend gets disconnected

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt2.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 143c1e4b0fefa6dda8e0e4bfa7a6da7d6e86653a Mon Sep 17 00:00:00 2001
From: Vitaly Kuznetsov <vkuznets at redhat.com>
Date: Mon, 8 Sep 2014 15:21:33 +0200
Subject: xen/blkback: unmap all persistent grants when frontend gets
 disconnected

commit 12ea729645ace01e08f9654df155622898d3aae6 upstream.

blkback does not unmap persistent grants when frontend goes to Closed
state (e.g. when blkfront module is being removed). This leads to the
following in guest's dmesg:

[  343.243825] xen:grant_table: WARNING: g.e. 0x445 still in use!
[  343.243825] xen:grant_table: WARNING: g.e. 0x42a still in use!
...

When load module -> use device -> unload module sequence is performed multiple times
it is possible to hit BUG() condition in blkfront module:

[  343.243825] kernel BUG at drivers/block/xen-blkfront.c:954!
[  343.243825] invalid opcode: 0000 [#1] SMP
[  343.243825] Modules linked in: xen_blkfront(-) ata_generic pata_acpi [last unloaded: xen_blkfront]
...
[  343.243825] Call Trace:
[  343.243825]  [<ffffffff814111ef>] ? unregister_xenbus_watch+0x16f/0x1e0
[  343.243825]  [<ffffffffa0016fbf>] blkfront_remove+0x3f/0x140 [xen_blkfront]
...
[  343.243825] RIP  [<ffffffffa0016aae>] blkif_free+0x34e/0x360 [xen_blkfront]
[  343.243825]  RSP <ffff88001eb8fdc0>

We don't need to keep these grants if we're disconnecting as frontend might already
forgot about them. Solve the issue by moving xen_blkbk_free_caches() call from
xen_blkif_free() to xen_blkif_disconnect().

Now we can see the following:
[  928.590893] xen:grant_table: WARNING: g.e. 0x587 still in use!
[  928.591861] xen:grant_table: WARNING: g.e. 0x372 still in use!
...
[  929.592146] xen:grant_table: freeing g.e. 0x587
[  929.597174] xen:grant_table: freeing g.e. 0x372
...

Backend does not keep persistent grants any more, reconnect works fine.

Signed-off-by: Vitaly Kuznetsov <vkuznets at redhat.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/block/xen-blkback/xenbus.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 3a8b810b4980..54f408963201 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -270,6 +270,9 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 		blkif->blk_rings.common.sring = NULL;
 	}

+	/* Remove all persistent grants and the cache of ballooned pages. */
+	xen_blkbk_free_caches(blkif);
+
 	return 0;
 }

@@ -281,9 +284,6 @@ static void xen_blkif_free(struct xen_blkif *blkif)
 	xen_blkif_disconnect(blkif);
 	xen_vbd_free(&blkif->vbd);

-	/* Remove all persistent grants and the cache of ballooned pages. */
-	xen_blkbk_free_caches(blkif);
-
 	/* Make sure everything is drained before shutting down */
 	BUG_ON(blkif->persistent_gnt_c != 0);
 	BUG_ON(atomic_read(&blkif->persistent_gnt_in_use) != 0);
--
2.1.0





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