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Subject[PATCH 17.5] blkcg: skip blkg printing if q isn't associated with disk
From 753d7ea85c1d8648a9edb84539849018631335ea Mon Sep 17 00:00:00 2001
From: Vivek Goyal <vgoyal@redhat.com>
Date: Mon, 5 Mar 2012 12:54:07 -0800

blk-cgroup printing code currently assumes that there is a device/disk
associated with every queue in the system, but modules like floppy,
can instantiate request queues without registering disk which can lead
to oops.

Skip the queue/blkg which don't have dev/disk associated with them.

-tj: Factored out backing_dev_info check into blkg_dev_name().

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
This causes series of minor conflicts with following patches. I'll
write about it in a reply to the top post.
Thanks.

block/blk-cgroup.c | 17 ++++++++++++++---
1 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 8742af3..7694236 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -951,13 +951,24 @@ static int blkiocg_file_write(struct cgroup *cgrp, struct cftype *cft,
return ret;
}

+static const char *blkg_dev_name(struct blkio_group *blkg)
+{
+ /* some drivers (floppy) instantiate a queue w/o disk registered */
+ if (blkg->q->backing_dev_info.dev)
+ return dev_name(blkg->q->backing_dev_info.dev);
+ return NULL;
+}
+
static void blkio_print_group_conf(struct cftype *cft, struct blkio_group *blkg,
struct seq_file *m)
{
- const char *dname = dev_name(blkg->q->backing_dev_info.dev);
+ const char *dname = blkg_dev_name(blkg);
int fileid = BLKIOFILE_ATTR(cft->private);
int rw = WRITE;

+ if (!dname)
+ return;
+
switch (blkg->plid) {
case BLKIO_POLICY_PROP:
if (blkg->conf.weight)
@@ -1049,9 +1060,9 @@ static int blkio_read_blkg_stats(struct blkio_cgroup *blkcg,

rcu_read_lock();
hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {
- const char *dname = dev_name(blkg->q->backing_dev_info.dev);
+ const char *dname = blkg_dev_name(blkg);

- if (BLKIOFILE_POLICY(cft->private) != blkg->plid)
+ if (!dname || BLKIOFILE_POLICY(cft->private) != blkg->plid)
continue;
if (pcpu)
cgroup_total += blkio_get_stat_cpu(blkg, cb, dname,
--
1.7.7.3


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