Re: [linus:master] [eventfs] 852e46e239: BUG:unable_to_handle_page_fault_for_address

[Linus Torvalds <torvalds@linux-foundation.org>]

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On Mon, 29 Jan 2024 at 14:35, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> So just replace all the d_instantiate() calls there with "d_add()"
> instead. I think that will fix it.

I can confirm that with the mutex deadlock removed and the d_add()
fix, at least things *look* superficially ok.

I didn't actually do anything with it. So it might be leaking dentry
refs like mad or something like that, but at least the obvious cases
look fine.

just for completeness, here's the fixup diff I used.

                  Linus

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 fs/tracefs/event_inode.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index cd6de3244442..5b307bb64f8f 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -230,7 +230,6 @@ static struct eventfs_inode *eventfs_find_events(struct dentry *dentry)
 {
 	struct eventfs_inode *ei;
 
-	mutex_lock(&eventfs_mutex);
 	do {
 		// The parent is stable because we do not do renames
 		dentry = dentry->d_parent;
@@ -247,7 +246,6 @@ static struct eventfs_inode *eventfs_find_events(struct dentry *dentry)
 		}
 		// Walk upwards until you find the events inode
 	} while (!ei->is_events);
-	mutex_unlock(&eventfs_mutex);
 
 	update_top_events_attr(ei, dentry->d_sb);
 
@@ -324,7 +322,7 @@ static struct dentry *lookup_file(struct dentry *dentry,
 	ti->flags = TRACEFS_EVENT_INODE;
 	ti->private = NULL;			// Directories have 'ei', files not
 
-	d_instantiate(dentry, inode);
+	d_add(dentry, inode);
 	fsnotify_create(dentry->d_parent->d_inode, dentry);
 	return eventfs_end_creating(dentry);
 };
@@ -365,7 +363,7 @@ static struct dentry *lookup_dir_entry(struct dentry *dentry,
         ei->dentry = dentry;	// Remove me!
 
 	inc_nlink(inode);
-	d_instantiate(dentry, inode);
+	d_add(dentry, inode);
 	inc_nlink(dentry->d_parent->d_inode);
 	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
 	return eventfs_end_creating(dentry);
@@ -786,7 +784,7 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
 
 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
 	inc_nlink(inode);
-	d_instantiate(dentry, inode);
+	d_add(dentry, inode);
 	inc_nlink(dentry->d_parent->d_inode);
 	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
 	tracefs_end_creating(dentry);