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do d_instantiate/unlock_new_inode combinations safely

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For anything NFS-exported we do _not_ want to unlock new inode
before it has grown an alias; original set of fixes got the
ordering right, but missed the nasty complication in case of
lockdep being enabled - unlock_new_inode() does
	lockdep_annotate_inode_mutex_key(inode)
which can only be done before anyone gets a chance to touch
->i_mutex.  Unfortunately, flipping the order and doing
unlock_new_inode() before d_instantiate() opens a window when
mkdir can race with open-by-fhandle on a guessed fhandle, leading
to multiple aliases for a directory inode and all the breakage
that follows from that.

	Correct solution: a new primitive (d_instantiate_new())
combining these two in the right order - lockdep annotate, then
d_instantiate(), then the rest of unlock_new_inode().  All
combinations of d_instantiate() with unlock_new_inode() should
be converted to that.

Cc: stable@kernel.org	# 2.6.29 and later
Tested-by: Mike Marshall <hubcap@omnibond.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2018-05-04 08:23:01 -04:00
parent d7760d638b
commit 1e2e547a93
14 changed files with 57 additions and 72 deletions
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16
fs/btrfs/inode.c
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@@ -6575,8 +6575,7 @@ static int btrfs_mknod(struct inode *dir, struct dentry *dentry,
goto out_unlock_inode;
} else {
btrfs_update_inode(trans, root, inode);
unlock_new_inode(inode);
d_instantiate(dentry, inode);
d_instantiate_new(dentry, inode);
}
out_unlock:
@@ -6652,8 +6651,7 @@ static int btrfs_create(struct inode *dir, struct dentry *dentry,
goto out_unlock_inode;
BTRFS_I(inode)->io_tree.ops = &btrfs_extent_io_ops;
unlock_new_inode(inode);
d_instantiate(dentry, inode);
d_instantiate_new(dentry, inode);
out_unlock:
btrfs_end_transaction(trans);
@@ -6798,12 +6796,7 @@ static int btrfs_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
if (err)
goto out_fail_inode;
d_instantiate(dentry, inode);
/*
* mkdir is special. We're unlocking after we call d_instantiate
* to avoid a race with nfsd calling d_instantiate.
*/
unlock_new_inode(inode);
d_instantiate_new(dentry, inode);
drop_on_err = 0;
out_fail:
@@ -10246,8 +10239,7 @@ static int btrfs_symlink(struct inode *dir, struct dentry *dentry,
goto out_unlock_inode;
}
unlock_new_inode(inode);
d_instantiate(dentry, inode);
d_instantiate_new(dentry, inode);
out_unlock:
btrfs_end_transaction(trans);