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Subject[37/80] bdi: Fix warnings in __mark_inode_dirty for /dev/zero and friends
2.6.35-stable review patch.  If anyone has any objections, please let us know.

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

From: Jan Kara <jack@suse.cz>

commit 692ebd17c2905313fff3c504c249c6a0faad16ec upstream.

Inodes of devices such as /dev/zero can get dirty for example via
utime(2) syscall or due to atime update. Backing device of such inodes
(zero_bdi, etc.) is however unable to handle dirty inodes and thus
__mark_inode_dirty complains. In fact, inode should be rather dirtied
against backing device of the filesystem holding it. This is generally a
good rule except for filesystems such as 'bdev' or 'mtd_inodefs'. Inodes
in these pseudofilesystems are referenced from ordinary filesystem
inodes and carry mapping with real data of the device. Thus for these
inodes we have to use inode->i_mapping->backing_dev_info as we did so
far. We distinguish these filesystems by checking whether sb->s_bdi
points to a non-trivial backing device or not.

Example: Assume we have an ext3 filesystem on /dev/sda1 mounted on /.
There's a device inode A described by a path "/dev/sdb" on this
filesystem. This inode will be dirtied against backing device "8:0"
after this patch. bdev filesystem contains block device inode B coupled
with our inode A. When someone modifies a page of /dev/sdb, it's B that
gets dirtied and the dirtying happens against the backing device "8:16".
Thus both inodes get filed to a correct bdi list.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/fs-writeback.c | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)

--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -28,8 +28,6 @@
#include <linux/buffer_head.h>
#include "internal.h"

-#define inode_to_bdi(inode) ((inode)->i_mapping->backing_dev_info)
-
/*
* We don't actually have pdflush, but this one is exported though /proc...
*/
@@ -62,6 +60,27 @@ int writeback_in_progress(struct backing
return !list_empty(&bdi->work_list);
}

+static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
+{
+ struct super_block *sb = inode->i_sb;
+ struct backing_dev_info *bdi = inode->i_mapping->backing_dev_info;
+
+ /*
+ * For inodes on standard filesystems, we use superblock's bdi. For
+ * inodes on virtual filesystems, we want to use inode mapping's bdi
+ * because they can possibly point to something useful (think about
+ * block_dev filesystem).
+ */
+ if (sb->s_bdi && sb->s_bdi != &noop_backing_dev_info) {
+ /* Some device inodes could play dirty tricks. Catch them... */
+ WARN(bdi != sb->s_bdi && bdi_cap_writeback_dirty(bdi),
+ "Dirtiable inode bdi %s != sb bdi %s\n",
+ bdi->name, sb->s_bdi->name);
+ return sb->s_bdi;
+ }
+ return bdi;
+}
+
static void bdi_queue_work(struct backing_dev_info *bdi,
struct wb_writeback_work *work)
{



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