Re: lockdep: inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R}usage.

From: Christoph Hellwig
Date: Tue Jan 19 2010 - 13:46:41 EST

On Fri, Jan 15, 2010 at 01:53:15PM +0100, Peter Zijlstra wrote:
> Well, I don't know enough about xfs (of filesystems in generic) to say
> that with any certainty, but I can imagine inode writeback from the sync
> that goes with umount to cause issues.
> If this inode reclaim is past all that and the filesystem is basically
> RO, then I don't think so and this could be considered a false positive,
> in which case we need an annotation for this.

The issue is a bit more complicated. In the unmount case
invalidate_inodes() is indeed called after the filesystem is effectively
read-only for user origination operations. But there's a miriad of
other invalidate_inodes() calls:

- fs/block_dev.c:__invalidate_device()

This gets called from block device codes for various kinds of
invalidations. Doesn't make any sense at all to me, but hey..

- fs/ext2/super.c:ext2_remount()

Appears like it's used to check for activate inodes during
remount. Very fishy usage, and could just be replaced with
a list walk without any I/O

- fs/gfs2/glock.c:gfs2_gl_hash_clear()

No idea.

- fs/gfs2/ops_fstype.c:fill_super()

Tries to kill all inodes in the fill_super error path, looks
very fishy.

- fs/ntfs/super.c:ntfs_fill_super()

Failure case of fill_super again, does not look very useful.A

- fs/smbfs/inode.c:smb_invalidate_inodes()

Used when a connection goes bad.

In short we can't generally rely on this only happening on a dead fs.

But in the end we abuse iprune_sem to work around a ref counting
problem. As long as we keep a reference to the superblock for each
inode on the dispose list the superblock can't go away and there's
no need for the lock at all.
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