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Subject[PATCH 02/11] vfs: More precise tests in d_invalidate

The current comments in d_invalidate about what and why it is doing
what it is doing are wildly off-base. Which is not surprising as
the comments date back to last minute bug fix of the 2.2 kernel.

The big fat lie of a comment said: If it's a directory, we can't drop
it for fear of somebody re-populating it with children (even though
dropping it would make it unreachable from that root, we still might
repopulate it if it was a working directory or similar).

The truth is that for remote filesystems the failure of d_revalidate
and d_weak_revalidate prevents us from populating or otherwise
inappropriately using a directory. For local filesystems and for
local directory removals the setting of S_DEAD prevents us from
populating or otherwise inappropriate using a directory.

The current rules are:
- To prevent mount point leaks dentries that are mount points or that
have childrent that are mount points may not be be unhashed.
- All dentries may be unhashed.
- Directories may be rehashed with d_materialise_unique

check_submounts_and_drop implements this already for well maintained
remote filesystems so implement the current rules in d_invalidate
by just calling check_submounts_and_drop.

The one difference between d_invalidate and check_submounts_and_drop
is that d_invalidate must respect it when a d_revalidate method has
earlier called d_drop so preserve the d_unhashed check in
d_invalidate.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/dcache.c | 38 ++++----------------------------------
1 files changed, 4 insertions(+), 34 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index c71c86f7780e..b0add629f5fe 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -613,9 +613,8 @@ EXPORT_SYMBOL(dput);
* @dentry: dentry to invalidate
*
* Try to invalidate the dentry if it turns out to be
- * possible. If there are other dentries that can be
- * reached through this one we can't delete it and we
- * return -EBUSY. On success we return 0.
+ * possible. If there are reasons not to delete it
+ * return -EBUSY. On success return 0.
*
* no dcache lock.
*/
@@ -630,38 +629,9 @@ int d_invalidate(struct dentry * dentry)
spin_unlock(&dentry->d_lock);
return 0;
}
- /*
- * Check whether to do a partial shrink_dcache
- * to get rid of unused child entries.
- */
- if (!list_empty(&dentry->d_subdirs)) {
- spin_unlock(&dentry->d_lock);
- shrink_dcache_parent(dentry);
- spin_lock(&dentry->d_lock);
- }
-
- /*
- * Somebody else still using it?
- *
- * If it's a directory, we can't drop it
- * for fear of somebody re-populating it
- * with children (even though dropping it
- * would make it unreachable from the root,
- * we might still populate it if it was a
- * working directory or similar).
- * We also need to leave mountpoints alone,
- * directory or not.
- */
- if (dentry->d_lockref.count > 1 && dentry->d_inode) {
- if (S_ISDIR(dentry->d_inode->i_mode) || d_mountpoint(dentry)) {
- spin_unlock(&dentry->d_lock);
- return -EBUSY;
- }
- }
-
- __d_drop(dentry);
spin_unlock(&dentry->d_lock);
- return 0;
+
+ return check_submounts_and_drop(dentry);
}
EXPORT_SYMBOL(d_invalidate);

--
1.7.5.4


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