From 6d0a8a90a5bbfd6befcb512fad6618608e8c0e86 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Fri, 10 Nov 2017 13:18:07 +0200 Subject: [PATCH] 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/dir.c | 117 ++++++++++++++++++----------------------- fs/overlayfs/namei.c | 3 ++ fs/overlayfs/readdir.c | 3 ++ 3 files changed, 58 insertions(+), 65 deletions(-) diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index f9788bc116a8..a1a7606d4891 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -181,11 +181,6 @@ static bool ovl_type_origin(struct dentry *dentry) return OVL_TYPE_ORIGIN(ovl_path_type(dentry)); } -static bool ovl_may_have_whiteouts(struct dentry *dentry) -{ - return ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry)); -} - static int ovl_create_upper(struct dentry *dentry, struct inode *inode, struct cattr *attr, struct dentry *hardlink) { @@ -301,37 +296,6 @@ static struct dentry *ovl_clear_empty(struct dentry *dentry, return ERR_PTR(err); } -static struct dentry *ovl_check_empty_and_clear(struct dentry *dentry) -{ - int err; - struct dentry *ret = NULL; - LIST_HEAD(list); - - err = ovl_check_empty_dir(dentry, &list); - if (err) { - ret = ERR_PTR(err); - goto out_free; - } - - /* - * When removing an empty opaque directory, then it makes no sense to - * replace it with an exact replica of itself. - * - * If upperdentry has whiteouts, clear them. - * - * Can race with copy-up, since we don't hold the upperdir mutex. - * Doesn't matter, since copy-up can't create a non-empty directory - * from an empty one. - */ - if (!list_empty(&list)) - ret = ovl_clear_empty(dentry, &list); - -out_free: - ovl_cache_free(&list); - - return ret; -} - static int ovl_set_upper_acl(struct dentry *upperdentry, const char *name, const struct posix_acl *acl) { @@ -623,7 +587,8 @@ static bool ovl_matches_upper(struct dentry *dentry, struct dentry *upper) return d_inode(ovl_dentry_upper(dentry)) == d_inode(upper); } -static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir) +static int ovl_remove_and_whiteout(struct dentry *dentry, + struct list_head *list) { struct dentry *workdir = ovl_workdir(dentry); struct inode *wdir = workdir->d_inode; @@ -638,8 +603,8 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir) if (WARN_ON(!workdir)) return -EROFS; - if (is_dir) { - opaquedir = ovl_check_empty_and_clear(dentry); + if (!list_empty(list)) { + opaquedir = ovl_clear_empty(dentry, list); err = PTR_ERR(opaquedir); if (IS_ERR(opaquedir)) goto out; @@ -694,7 +659,8 @@ static int ovl_remove_and_whiteout(struct dentry *dentry, bool is_dir) goto out_d_drop; } -static int ovl_remove_upper(struct dentry *dentry, bool is_dir) +static int ovl_remove_upper(struct dentry *dentry, bool is_dir, + struct list_head *list) { struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent); struct inode *dir = upperdir->d_inode; @@ -702,10 +668,8 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir) struct dentry *opaquedir = NULL; int err; - /* Redirect/origin dir can be !ovl_lower_positive && not clean */ - if (is_dir && (ovl_dentry_get_redirect(dentry) || - ovl_may_have_whiteouts(dentry))) { - opaquedir = ovl_check_empty_and_clear(dentry); + if (!list_empty(list)) { + opaquedir = ovl_clear_empty(dentry, list); err = PTR_ERR(opaquedir); if (IS_ERR(opaquedir)) goto out; @@ -746,11 +710,26 @@ static int ovl_remove_upper(struct dentry *dentry, bool is_dir) return err; } +static bool ovl_pure_upper(struct dentry *dentry) +{ + return !ovl_dentry_lower(dentry) && + !ovl_test_flag(OVL_WHITEOUTS, d_inode(dentry)); +} + static int ovl_do_remove(struct dentry *dentry, bool is_dir) { int err; bool locked = false; const struct cred *old_cred; + bool lower_positive = ovl_lower_positive(dentry); + LIST_HEAD(list); + + /* No need to clean pure upper removed by vfs_rmdir() */ + if (is_dir && (lower_positive || !ovl_pure_upper(dentry))) { + err = ovl_check_empty_dir(dentry, &list); + if (err) + goto out; + } err = ovl_want_write(dentry); if (err) @@ -765,10 +744,10 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir) goto out_drop_write; old_cred = ovl_override_creds(dentry->d_sb); - if (!ovl_lower_positive(dentry)) - err = ovl_remove_upper(dentry, is_dir); + if (!lower_positive) + err = ovl_remove_upper(dentry, is_dir, &list); else - err = ovl_remove_and_whiteout(dentry, is_dir); + err = ovl_remove_and_whiteout(dentry, &list); revert_creds(old_cred); if (!err) { if (is_dir) @@ -780,6 +759,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir) out_drop_write: ovl_drop_write(dentry); out: + ovl_cache_free(&list); return err; } @@ -915,6 +895,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, bool samedir = olddir == newdir; struct dentry *opaquedir = NULL; const struct cred *old_cred = NULL; + LIST_HEAD(list); err = -EINVAL; if (flags & ~(RENAME_EXCHANGE | RENAME_NOREPLACE)) @@ -929,6 +910,27 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, if (!overwrite && !ovl_can_move(new)) goto out; + if (overwrite && new_is_dir && !ovl_pure_upper(new)) { + err = ovl_check_empty_dir(new, &list); + if (err) + goto out; + } + + if (overwrite) { + if (ovl_lower_positive(old)) { + if (!ovl_dentry_is_whiteout(new)) { + /* Whiteout source */ + flags |= RENAME_WHITEOUT; + } else { + /* Switch whiteouts */ + flags |= RENAME_EXCHANGE; + } + } else if (is_dir && ovl_dentry_is_whiteout(new)) { + flags |= RENAME_EXCHANGE; + cleanup_whiteout = true; + } + } + err = ovl_want_write(old); if (err) goto out; @@ -952,9 +954,8 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, old_cred = ovl_override_creds(old->d_sb); - if (overwrite && new_is_dir && (ovl_type_merge_or_lower(new) || - ovl_may_have_whiteouts(new))) { - opaquedir = ovl_check_empty_and_clear(new); + if (!list_empty(&list)) { + opaquedir = ovl_clear_empty(new, &list); err = PTR_ERR(opaquedir); if (IS_ERR(opaquedir)) { opaquedir = NULL; @@ -962,21 +963,6 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, } } - if (overwrite) { - if (ovl_lower_positive(old)) { - if (!ovl_dentry_is_whiteout(new)) { - /* Whiteout source */ - flags |= RENAME_WHITEOUT; - } else { - /* Switch whiteouts */ - flags |= RENAME_EXCHANGE; - } - } else if (is_dir && ovl_dentry_is_whiteout(new)) { - flags |= RENAME_EXCHANGE; - cleanup_whiteout = true; - } - } - old_upperdir = ovl_dentry_upper(old->d_parent); new_upperdir = ovl_dentry_upper(new->d_parent); @@ -1094,6 +1080,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, ovl_drop_write(old); out: dput(opaquedir); + ovl_cache_free(&list); return err; } 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; } diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index a7e45e6cd732..7dfe381c2cd8 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -862,8 +862,11 @@ int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list) int err; struct ovl_cache_entry *p, *n; struct rb_root root = RB_ROOT; + const struct cred *old_cred; + old_cred = ovl_override_creds(dentry->d_sb); err = ovl_dir_read_merged(dentry, list, &root); + revert_creds(old_cred); if (err) return err; -- 2.45.2