[SRU][FOCAL][PATCH 1/2] UBUNTU: SAUCE: Revert "UBUNTU: SAUCE: shiftfs: fix dentry revalidation"

[Christian Brauner]

BugLink: https://bugs.launchpad.net/bugs/1884767

With patch cfaa482afb97 ("UBUNTU: SAUCE: shiftfs: fix dentry revalidation")
we tried to fix
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1872757 but it
introduces a regression for shiftfs on btrfs users. Creating a btrfs
subvolume, deleting it, and then trying to recreate it will cause EEXIST
to be returned or the file be left in a half-created state. Faulty
behavior such as this can be reproduced via:

btrfs subvolume create my-subvol
ls -al my-subvol
btrfs subvolume delete my-subvol

We thus need to revert this change restoring the old behavior.This will
briefly resurface https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1872757
which is fixed in a follow-up patch on top of this revert. We simply
split out the minimal fix into a separate tiny patch.

This reverts commit cfaa482afb97e3c05d020af80b897b061109d51f.

Cc: Seth Forshee <seth.forshee at canonical.com>
Signed-off-by: Christian Brauner <christian.brauner at ubuntu.com>
---
 fs/shiftfs.c | 45 ++++++++++++++++++++++++++++++++-------------
 1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/fs/shiftfs.c b/fs/shiftfs.c
index f5c709805fb8..5d88193b41db 100644
--- a/fs/shiftfs.c
+++ b/fs/shiftfs.c
@@ -240,17 +240,19 @@ static int shiftfs_d_weak_revalidate(struct dentry *dentry, unsigned int flags)
 	int err = 1;
 	struct dentry *lowerd = dentry->d_fsdata;
 
-	if (lowerd->d_flags & DCACHE_OP_WEAK_REVALIDATE) {
+	if (d_is_negative(lowerd) != d_is_negative(dentry))
+		return 0;
+
+	if ((lowerd->d_flags & DCACHE_OP_WEAK_REVALIDATE))
 		err = lowerd->d_op->d_weak_revalidate(lowerd, flags);
-		if (err < 0)
-			return err;
-	}
 
 	if (d_really_is_positive(dentry)) {
 		struct inode *inode = d_inode(dentry);
 		struct inode *loweri = d_inode(lowerd);
 
 		shiftfs_copyattr(loweri, inode);
+		if (!inode->i_nlink)
+			err = 0;
 	}
 
 	return err;
@@ -261,25 +263,23 @@ static int shiftfs_d_revalidate(struct dentry *dentry, unsigned int flags)
 	int err = 1;
 	struct dentry *lowerd = dentry->d_fsdata;
 
+	if (d_unhashed(lowerd) ||
+	    ((d_is_negative(lowerd) != d_is_negative(dentry))))
+		return 0;
+
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
 
-	if (lowerd->d_flags & DCACHE_OP_REVALIDATE) {
+	if ((lowerd->d_flags & DCACHE_OP_REVALIDATE))
 		err = lowerd->d_op->d_revalidate(lowerd, flags);
-		if (err < 0)
-			return err;
-		if (!err) {
-			if (!(flags & LOOKUP_RCU))
-				d_invalidate(lowerd);
-			return -ESTALE;
-		}
-	}
 
 	if (d_really_is_positive(dentry)) {
 		struct inode *inode = d_inode(dentry);
 		struct inode *loweri = d_inode(lowerd);
 
 		shiftfs_copyattr(loweri, inode);
+		if (!inode->i_nlink)
+			err = 0;
 	}
 
 	return err;
@@ -736,6 +736,24 @@ static int shiftfs_fiemap(struct inode *inode,
 	return err;
 }
 
+static int shiftfs_tmpfile(struct inode *dir, struct dentry *dentry,
+			   umode_t mode)
+{
+	int err;
+	const struct cred *oldcred;
+	struct dentry *lowerd = dentry->d_fsdata;
+	struct inode *loweri = dir->i_private;
+
+	if (!loweri->i_op->tmpfile)
+		return -EOPNOTSUPP;
+
+	oldcred = shiftfs_override_creds(dir->i_sb);
+	err = loweri->i_op->tmpfile(loweri, lowerd, mode);
+	revert_creds(oldcred);
+
+	return err;
+}
+
 static int shiftfs_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	struct dentry *lowerd = dentry->d_fsdata;
@@ -1002,6 +1020,7 @@ static const struct inode_operations shiftfs_file_inode_operations = {
 	.listxattr	= shiftfs_listxattr,
 	.permission	= shiftfs_permission,
 	.setattr	= shiftfs_setattr,
+	.tmpfile	= shiftfs_tmpfile,
 };
 
 static const struct inode_operations shiftfs_special_inode_operations = {

base-commit: 51ee04d9d3b464e9aa8509013779491f0b001ebc
-- 
2.27.0