From 6d0a8a90a5bbfd6befcb512fad6618608e8c0e86 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Fri, 10 Nov 2017 13:18:07 +0200 Subject: ovl: take lower dir inode mutex outside upper sb_writers lock The functions ovl_lower_positive() and ovl_check_empty_dir() both take inode mutex on the real lower dir under ovl_want_write() which takes the upper_mnt sb_writers lock. While this is not a clear locking order or layering violation, it creates an undesired lock dependency between two unrelated layers for no good reason. This lock dependency materializes to a false(?) positive lockdep warning when calling rmdir() on a nested overlayfs, where both nested and underlying overlayfs both use the same fs type as upper layer. rmdir() on the nested overlayfs creates the lock chain: sb_writers of upper_mnt (e.g. tmpfs) in ovl_do_remove() ovl_i_mutex_dir_key[] of lower overlay dir in ovl_lower_positive() rmdir() on the underlying overlayfs creates the lock chain in reverse order: ovl_i_mutex_dir_key[] of lower overlay dir in vfs_rmdir() sb_writers of nested upper_mnt (e.g. tmpfs) in ovl_do_remove() To rid of the unneeded locking dependency, move both ovl_lower_positive() and ovl_check_empty_dir() to before ovl_want_write() in rmdir() and rename() implementation. This change spreads the pieces of ovl_check_empty_and_clear() directly inside the rmdir()/rename() implementations so the helper is no longer needed and removed. Signed-off-by: Amir Goldstein Signed-off-by: Miklos Szeredi --- fs/overlayfs/namei.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'fs/overlayfs/namei.c') diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c index beb945e1963c..926248e1de04 100644 --- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -774,6 +774,7 @@ bool ovl_lower_positive(struct dentry *dentry) struct ovl_entry *oe = dentry->d_fsdata; struct ovl_entry *poe = dentry->d_parent->d_fsdata; const struct qstr *name = &dentry->d_name; + const struct cred *old_cred; unsigned int i; bool positive = false; bool done = false; @@ -789,6 +790,7 @@ bool ovl_lower_positive(struct dentry *dentry) if (!ovl_dentry_upper(dentry)) return true; + old_cred = ovl_override_creds(dentry->d_sb); /* Positive upper -> have to look up lower to see whether it exists */ for (i = 0; !done && !positive && i < poe->numlower; i++) { struct dentry *this; @@ -818,6 +820,7 @@ bool ovl_lower_positive(struct dentry *dentry) dput(this); } } + revert_creds(old_cred); return positive; } -- cgit v1.2.3