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dcache: close d_move race in d_splice_alias

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d_splice_alias will d_move an IS_ROOT() directory dentry into place if
one exists.  This should be safe as long as the dentry remains IS_ROOT,
but I can't see what guarantees that: once we drop the i_lock all we
hold here is the i_mutex on an unrelated parent directory.

Instead copy the logic of d_materialise_unique.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
J. Bruce Fields 2014-02-17 17:45:56 -05:00 committed by Al Viro
parent 3f70bd51cb
commit 75a2352d01
1 changed files with 6 additions and 1 deletions
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7
fs/dcache.c
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@ -2676,9 +2676,14 @@ struct dentry *d_splice_alias(struct inode *inode, struct dentry *dentry)
new = __d_find_alias(inode, 1);
if (new) {
BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
write_seqlock(&rename_lock);
__d_materialise_dentry(dentry, new);
write_sequnlock(&rename_lock);
__d_drop(new);
_d_rehash(new);
spin_unlock(&new->d_lock);
spin_unlock(&inode->i_lock);
security_d_instantiate(new, inode);
d_move(new, dentry);
iput(inode);
} else {
/* already taking inode->i_lock, so d_add() by hand */