[PATCH 1/2] dcache: don't leave negative dentries in casefolded directories

[Christian Brauner <brauner@kernel.org>]

ext4, f2fs and tmpfs keep negative dentries out of casefolded
directories. A negative dentry remembers one spelling of the name and
the next create() through it would write that spelling to disk.

So their ->lookup() doesn't cache a miss and their ->unlink() and
->rmdir() call d_invalidate() on the dentry so that d_delete() doesn't
turn it into a negative dentry.

But d_invalidate() is the wrong primitive for that. It's for a name that
went stale. It walks the subtree, prunes it and detaches every mount it
finds, under namespace_sem, and here that runs from inside the
filesystem's own directory operation. ext4_rmdir() does it with the
journal handle still open and ext4_unlink() does it even when the
unlink failed. All anyone wanted is the unhash.

So d_delete() now unhashes the dentry when the parent is casefolded,
next to the dentry-negative sysctl that does the same for every
directory. ext4, f2fs and tmpfs drop their d_invalidate() calls.

Nothing changes for a casefolded directory. A miss still isn't cached
and a removed name still doesn't leave a negative dentry behind. The
target of a rename over an existing name, which tmpfs also passes
through shmem_unlink(), doesn't turn negative either. vfs_rename()
detaches its mounts and d_move() unhashes it. A failed unlink or rmdir
now leaves the dentry hashed and its mounts in place, as in any other
directory.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/dcache.c     |  8 +++++++-
 fs/ext4/namei.c | 18 ------------------
 fs/f2fs/namei.c |  9 ---------
 mm/shmem.c      |  7 -------
 4 files changed, 7 insertions(+), 35 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index efd9332c8407..f5cbb2e24e53 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2746,6 +2746,12 @@ struct dentry *d_hash_and_lookup(struct dentry *dir, struct qstr *name)
 	return d_lookup(dir, name);
 }
 
+static __always_inline bool d_delete_drop(struct dentry *dentry)
+{
+	return dentry_negative_policy ||
+	       IS_CASEFOLDED(d_inode(dentry->d_parent));
+}
+
 /*
  * When a file is deleted, we have two options:
  * - turn this dentry into a negative dentry
@@ -2777,7 +2783,7 @@ void d_delete(struct dentry * dentry)
 	 * Are we the only user?
 	 */
 	if (dentry->d_lockref.count == 1) {
-		if (dentry_negative_policy)
+		if (d_delete_drop(dentry))
 			__d_drop(dentry);
 		dentry->d_flags &= ~DCACHE_CANT_MOUNT;
 		dentry_unlink_inode(dentry);
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 6e0630a49e48..c4b1121471e6 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -3209,15 +3209,6 @@ static int ext4_rmdir(struct inode *dir, struct dentry *dentry)
 	ext4_fc_track_unlink(handle, dentry);
 	retval = ext4_mark_inode_dirty(handle, dir);
 
-	/* VFS negative dentries are incompatible with Encoding and
-	 * Case-insensitiveness. Eventually we'll want avoid
-	 * invalidating the dentries here, alongside with returning the
-	 * negative dentries at ext4_lookup(), when it is better
-	 * supported by the VFS for the CI case.
-	 */
-	if (IS_ENABLED(CONFIG_UNICODE) && IS_CASEFOLDED(dir))
-		d_invalidate(dentry);
-
 end_rmdir:
 	brelse(bh);
 	if (handle)
@@ -3320,15 +3311,6 @@ static int ext4_unlink(struct inode *dir, struct dentry *dentry)
 
 	retval = __ext4_unlink(dir, &dentry->d_name, d_inode(dentry), dentry);
 
-	/* VFS negative dentries are incompatible with Encoding and
-	 * Case-insensitiveness. Eventually we'll want avoid
-	 * invalidating the dentries here, alongside with returning the
-	 * negative dentries at ext4_lookup(), when it is  better
-	 * supported by the VFS for the CI case.
-	 */
-	if (IS_ENABLED(CONFIG_UNICODE) && IS_CASEFOLDED(dir))
-		d_invalidate(dentry);
-
 out_trace:
 	trace_ext4_unlink_exit(dentry, retval);
 	return retval;
diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
index 233c07fec171..30f6b8448eee 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -631,15 +631,6 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
 	if (err)
 		goto out;
 
-	/* VFS negative dentries are incompatible with Encoding and
-	 * Case-insensitiveness. Eventually we'll want avoid
-	 * invalidating the dentries here, alongside with returning the
-	 * negative dentries at f2fs_lookup(), when it is better
-	 * supported by the VFS for the CI case.
-	 */
-	if (IS_ENABLED(CONFIG_UNICODE) && IS_CASEFOLDED(dir))
-		d_invalidate(dentry);
-
 	if (IS_DIRSYNC(dir))
 		err = f2fs_sync_fs(F2FS_I_SB(dir)->sb, 1);
 out:
diff --git a/mm/shmem.c b/mm/shmem.c
index 0d891ade18b5..5a353ac32573 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3953,13 +3953,6 @@ static int shmem_unlink(struct inode *dir, struct dentry *dentry)
 	inode_inc_iversion(dir);
 	simple_unlink(dir, dentry);
 
-	/*
-	 * For now, VFS can't deal with case-insensitive negative dentries, so
-	 * we invalidate them
-	 */
-	if (IS_ENABLED(CONFIG_UNICODE) && IS_CASEFOLDED(dir))
-		d_invalidate(dentry);
-
 	return 0;
 }
 

-- 
2.53.0