Commit 692ebd17 authored Sep 21, 2010 by Jan Kara Committed by Jens Axboe Sep 22, 2010

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



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>

parent 371d217e

fs/fs-writeback.c

+21 −2

Original line number	Diff line number	Diff line
		@@ -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)
		{