[PATCH v7 6/8] ovl: recalc d_ino for dir cache in non-samefs case

[Amir Goldstein <amir73il@gmail.com>]

st_ino returned by stat(2) for dirs on non-samefs is the non persistent
overlay i_ino. Update the dir cache with volatile overlay i_ino values.
Overlay dir cache and inode cache may get out of sync after child inodes
exit and re-enter inode cache. This means that user may see inconsistent
st_ino/d_ino, but user can already see inconsistent st_ino of same object
in different times, so this is better than nothing.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/readdir.c | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 4f2479b6ef91..4ec95806285e 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -120,6 +120,10 @@ static bool ovl_calc_d_ino(struct ovl_readdir_data *rdd,
 	if (!rdd->dentry)
 		return false;
 
+	/* Always recalc d_ino from i_ino for dir on non-samefs */
+	if (p->type == DT_DIR && !ovl_same_sb(rdd->dentry->d_sb))
+		return true;
+
 	/* Always recalc d_ino for parent */
 	if (strcmp(p->name, "..") == 0)
 		return true;
@@ -459,9 +463,6 @@ static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
 	u64 ino = p->real_ino;
 	int err = 0;
 
-	if (!ovl_same_sb(dir->d_sb))
-		goto out;
-
 	if (p->name[0] == '.') {
 		if (p->len == 1) {
 			this = dget(dir);
@@ -484,6 +485,19 @@ static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
 	}
 
 get:
+	/*
+	 * st_ino for dirs on non-samefs is the non persistent overlay i_ino.
+	 * Update the dir cache with volatile overlay i_ino, even though
+	 * dir cache and inode cache may get out of sync after child inodes
+	 * exit and re-enter inode cache. This means that user may see
+	 * inconsistent st_ino/d_ino, but user can already see inconsistent
+	 * st_ino of same object in different times.
+	 */
+	if (p->type == DT_DIR && !ovl_same_sb(dir->d_sb)) {
+		ino = this->d_inode->i_ino;
+		goto out;
+	}
+
 	type = ovl_path_type(this);
 	if (OVL_TYPE_ORIGIN(type)) {
 		struct kstat stat;
@@ -494,7 +508,8 @@ static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
 		if (err)
 			goto fail;
 
-		WARN_ON_ONCE(dir->d_sb->s_dev != stat.dev);
+		if (ovl_same_sb(dir->d_sb))
+			WARN_ON_ONCE(dir->d_sb->s_dev != stat.dev);
 		ino = stat.ino;
 	}
 
-- 
2.7.4