Forwarded: [PATCH] namei: add debug printk to trace parent inode lock state

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***

Subject: [PATCH] namei: add debug printk to trace parent inode lock state
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Add debug printk statements to trace the parent directory inode rwsem
state through the symlink creation path. This helps identify which
component is dropping the parent inode's i_rwsem between start_dirop()
and end_dirop(), causing the unbalanced unlock WARNING in
filename_symlinkat().

The printk traces:
- rwsem owner/count after start_dirop() acquires the lock
- rwsem owner/count after vfs_symlink() returns
- rwsem owner/count at end_dirop() just before the unlock
- dentry->d_parent and path->dentry at each point

This is a temporary diagnostic patch and should be reverted once the
root cause is identified.

Reported-by: syzbot+2ed46b6b748df855347f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=2ed46b6b748df855347f
Signed-off-by: Deepanshu Kartikey <Kartikey406@gmail.com>
---
 fs/namei.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 58f715f7657e..9584ff6dff47 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2944,6 +2944,11 @@ struct dentry *start_dirop(struct dentry *parent, struct qstr *name,
 void end_dirop(struct dentry *de)
 {
 	if (!IS_ERR(de)) {
+		struct inode *dir = d_inode(de->d_parent);
+		pr_warn("DEBUG: end_dirop: de=%px parent=%px inode=%px rwsem count=%ld owner=%px current=%px\n",
+			de, de->d_parent, dir,
+			atomic_long_read(&dir->i_rwsem.count),
+			READ_ONCE(dir->i_rwsem.owner), current);
 		inode_unlock(de->d_parent->d_inode);
 		dput(de);
 	}
@@ -4922,7 +4927,9 @@ static struct dentry *filename_create(int dfd, struct filename *name,
 	dentry = start_dirop(path->dentry, &last, reval_flag | create_flags);
 	if (IS_ERR(dentry))
 		goto out_drop_write;
-
+	pr_warn("DEBUG: after start_dirop: dentry=%px parent=%px parent_inode=%px rwsem owner=%px current=%px\n",
+		dentry, dentry->d_parent, d_inode(dentry->d_parent),
+		(void *)atomic_long_read(&d_inode(dentry->d_parent)->i_rwsem.count), current);
 	if (unlikely(error))
 		goto fail;
 
@@ -4959,7 +4966,10 @@ EXPORT_SYMBOL(start_creating_path);
  */
 void end_creating_path(const struct path *path, struct dentry *dentry)
 {
-	end_creating(dentry);
+	if (!IS_ERR(dentry)) {
+		inode_unlock(d_inode(path->dentry));
+		dput(dentry);
+	}
 	mnt_drop_write(path->mnt);
 	path_put(path);
 }
@@ -5639,6 +5649,10 @@ int filename_symlinkat(struct filename *from, int newdfd, struct filename *to)
 	if (!error)
 		error = vfs_symlink(mnt_idmap(path.mnt), path.dentry->d_inode,
 				    dentry, from->name, &delegated_inode);
+	pr_warn("DEBUG: after vfs_symlink: error=%d dentry=%px parent=%px parent_inode=%px rwsem owner=%px path_dentry=%px path_inode=%px\n",
+		error, dentry, dentry->d_parent, d_inode(dentry->d_parent),
+		(void *)atomic_long_read(&d_inode(path.dentry)->i_rwsem.count),
+		path.dentry, d_inode(path.dentry));
 	end_creating_path(&path, dentry);
 	if (is_delegated(&delegated_inode)) {
 		error = break_deleg_wait(&delegated_inode);
-- 
2.43.0