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bdi: Fix warnings in __mark_inode_dirty for /dev/zero and friends

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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.

Cc: stable@kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Jan Kara 2010-09-21 11:51:01 +02:00 committed by Jens Axboe
parent 371d217ee1
commit 692ebd17c2
1 changed files with 21 additions and 2 deletions
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23
fs/fs-writeback.c
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@ -52,8 +52,6 @@ struct wb_writeback_work {
#define CREATE_TRACE_POINTS
#include <trace/events/writeback.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...
*/
@ -71,6 +69,27 @@ int writeback_in_progress(struct backing_dev_info *bdi)
return test_bit(BDI_writeback_running, &bdi->state);
}
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)
{