Regression on linux-next (next-20250120)

[Al Viro]

On Wed, Jan 29, 2025 at 08:13:02AM +0100, Greg Kroah-Hartman wrote:

> > Both are needed, actually.  Slightly longer term I would rather
> > split full_proxy_{read,write,lseek}() into short and full variant,
> > getting rid of the "check which pointer is non-NULL" and killed
> > the two remaining users of debugfs_real_fops() outside of
> > fs/debugfs/file.c; then we could union these ->..._fops pointers,
> > but until then they need to be initialized.
> > 
> > And yes, ->methods obviously needs to be initialized.
> > 
> > Al, bloody embarrassed ;-/
> 
> No worries, want to send a patch to fix both of these up so we can fix
> up Linus's tree now?

[PATCH] Fix the missing initializations in __debugfs_file_get()
    
both method table pointers in debugfs_fsdata need to be initialized,
obviously, and calculating the bitmap of present methods would also
go better if we start with initialized state.
    
Fixes: 41a0ecc0997c "debugfs: get rid of dynamically allocation proxy_ops"
Fucked-up-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
---
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index e33cc77699cd..69e9ddcb113d 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -94,6 +94,7 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
 		fsd = d_fsd;
 	} else {
 		struct inode *inode = dentry->d_inode;
+		unsigned int methods = 0;
 
 		if (WARN_ON(mode == DBGFS_GET_ALREADY))
 			return -EINVAL;
@@ -106,25 +107,28 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
 			const struct debugfs_short_fops *ops;
 			ops = fsd->short_fops = DEBUGFS_I(inode)->short_fops;
 			if (ops->llseek)
-				fsd->methods |= HAS_LSEEK;
+				methods |= HAS_LSEEK;
 			if (ops->read)
-				fsd->methods |= HAS_READ;
+				methods |= HAS_READ;
 			if (ops->write)
-				fsd->methods |= HAS_WRITE;
+				methods |= HAS_WRITE;
+			fsd->real_fops = NULL;
 		} else {
 			const struct file_operations *ops;
 			ops = fsd->real_fops = DEBUGFS_I(inode)->real_fops;
 			if (ops->llseek)
-				fsd->methods |= HAS_LSEEK;
+				methods |= HAS_LSEEK;
 			if (ops->read)
-				fsd->methods |= HAS_READ;
+				methods |= HAS_READ;
 			if (ops->write)
-				fsd->methods |= HAS_WRITE;
+				methods |= HAS_WRITE;
 			if (ops->unlocked_ioctl)
-				fsd->methods |= HAS_IOCTL;
+				methods |= HAS_IOCTL;
 			if (ops->poll)
-				fsd->methods |= HAS_POLL;
+				methods |= HAS_POLL;
+			fsd->short_fops = NULL;
 		}
+		fsd->methods = methods;
 		refcount_set(&fsd->active_users, 1);
 		init_completion(&fsd->active_users_drained);
 		INIT_LIST_HEAD(&fsd->cancellations);