[PATCH] eventfs: Fix events beyond NAME_MAX blocking tasks

[Beau Belgrave <beaub@linux.microsoft.com>]

Eventfs uses simple_lookup(), however, it will fail if the name of the
entry is beyond NAME_MAX length. When this error is encountered, eventfs
still tries to create dentries instead of skipping the dentry creation.
When the dentry is attempted to be created in this state d_wait_lookup()
will loop forever, waiting for the lookup to be removed.

Fix eventfs to return the error in simple_lookup() back to the caller
instead of continuing to try to create the dentry.

Fixes: 63940449555e ("eventfs: Implement eventfs lookup, read, open functions")
Link: https://lore.kernel.org/linux-trace-kernel/20231208183601.GA46-beaub@linux.microsoft.com/
Signed-off-by: Beau Belgrave <beaub@linux.microsoft.com>
---
Please note the fixes tag is the first add of simple_lookup logic, there
have been other changes beyond that may be a better fit to targetting.

 fs/tracefs/event_inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index f8a594a50ae6..d2c06ba26db4 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -561,6 +561,8 @@ static struct dentry *eventfs_root_lookup(struct inode *dir,
 		if (strcmp(ei_child->name, name) != 0)
 			continue;
 		ret = simple_lookup(dir, dentry, flags);
+		if (IS_ERR(ret))
+			goto out;
 		create_dir_dentry(ei, ei_child, ei_dentry, true);
 		created = true;
 		break;
@@ -583,6 +585,8 @@ static struct dentry *eventfs_root_lookup(struct inode *dir,
 			if (r <= 0)
 				continue;
 			ret = simple_lookup(dir, dentry, flags);
+			if (IS_ERR(ret))
+				goto out;
 			create_file_dentry(ei, i, ei_dentry, name, mode, cdata,
 					   fops, true);
 			break;
-- 
2.34.1