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

Steven Rostedt
2024-01-31T15:58:34Z

On Tue, 30 Jan 2024 11:54:56 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> If you do run the full tracefs tests on the whole series, and there
> are no other major problems, I'll happily take it all for 6.8. And
> yes, even mark it for stable. I think the other bugs are much harder
> to hit, but I do think they exist. And code deletion is always good.
>
> So give it the full test attention, and *if* it all still looks good
> and there are no new subtle issues that crop up, let's just put this
> saga behind us asap.

BTW, I ran my full test suite on your patches with the below updates and it
all passed. Note, I did not run the "bisectable" portion of my test. That
is, the part that runs tests on each patch in the series. Because I know
that fails. I just ran the tests on the last applied patch.

I can break up and clean up the patches so that they are bisectable, and if
that passes the bisectable portion of my tests, I can still send them to
you for 6.8. I think this does fix a lot of hidden bugs, and would like all
this to go back to 6.6 when the eventfs was first introduced.

-- Steve

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index acdc797bd9c0..31cbe38739fa 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -74,7 +74,8 @@ static void release_ei(struct kref *ref)
{
struct eventfs_inode *ei = container_of(ref, struct eventfs_inode, kref);
kfree(ei->entry_attrs);
- kfree(ei);
+ kfree_const(ei->name);
+ kfree_rcu(ei, rcu);
}

static inline void put_ei(struct eventfs_inode *ei)
@@ -348,8 +349,7 @@ static struct dentry *lookup_file(struct eventfs_inode *parent_ei,
inode->i_ino = EVENTFS_FILE_INODE_INO;

ti = get_tracefs(inode);
- ti->flags = TRACEFS_EVENT_INODE;
- ti->private = NULL; // Directories have 'ei', files not
+ ti->flags |= TRACEFS_EVENT_INODE;

// Files have their parent's ei as their fsdata
dentry->d_fsdata = get_ei(parent_ei);
@@ -388,7 +388,8 @@ static struct dentry *lookup_dir_entry(struct dentry *dentry,
inode->i_ino = eventfs_dir_ino(ei);

ti = get_tracefs(inode);
- ti->flags = TRACEFS_EVENT_INODE;
+ ti->flags |= TRACEFS_EVENT_INODE;
+ /* Only directories have ti->private set to an ei, not files */
ti->private = ei;

dentry->d_fsdata = get_ei(ei);
@@ -402,17 +403,20 @@ static struct dentry *lookup_dir_entry(struct dentry *dentry,

static inline struct eventfs_inode *alloc_ei(const char *name)
{
- int namesize = strlen(name) + 1;
- struct eventfs_inode *ei = kzalloc(sizeof(*ei) + namesize, GFP_KERNEL);
+ struct eventfs_inode *ei = kzalloc(sizeof(*ei), GFP_KERNEL);

- if (ei) {
- memcpy((char *)ei->name, name, namesize);
- kref_init(&ei->kref);
+ if (!ei)
+ return NULL;
+
+ ei->name = kstrdup_const(name, GFP_KERNEL);
+ if (!ei->name) {
+ kfree(ei);
+ return NULL;
}
+ kref_init(&ei->kref);
return ei;
}

-
/**
* eventfs_d_release - dentry is going away
* @dentry: dentry which has the reference to remove.
@@ -750,7 +754,7 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
INIT_LIST_HEAD(&ei->list);

ti = get_tracefs(inode);
- ti->flags = TRACEFS_EVENT_INODE | TRACEFS_EVENT_TOP_INODE;
+ ti->flags |= TRACEFS_EVENT_INODE | TRACEFS_EVENT_TOP_INODE;
ti->private = ei;

inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
@@ -847,5 +851,6 @@ void eventfs_remove_events_dir(struct eventfs_inode *ei)
* sticks around while the other ei->dentry are created
* and destroyed dynamically.
*/
+ d_invalidate(dentry);
dput(dentry);
}
diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 64122787e5d0..cf90ea86baf8 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -38,8 +38,6 @@ static struct inode *tracefs_alloc_inode(struct super_block *sb)
if (!ti)
return NULL;

- ti->flags = 0;
-
return &ti->vfs_inode;
}

@@ -506,75 +504,6 @@ struct dentry *tracefs_end_creating(struct dentry *dentry)
return dentry;
}

-/**
- * eventfs_start_creating - start the process of creating a dentry
- * @name: Name of the file created for the dentry
- * @parent: The parent dentry where this dentry will be created
- *
- * This is a simple helper function for the dynamically created eventfs
- * files. When the directory of the eventfs files are accessed, their
- * dentries are created on the fly. This function is used to start that
- * process.
- */
-struct dentry *eventfs_start_creating(const char *name, struct dentry *parent)
-{
- struct dentry *dentry;
- int error;
-
- /* Must always have a parent. */
- if (WARN_ON_ONCE(!parent))
- return ERR_PTR(-EINVAL);
-
- error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
- &tracefs_mount_count);
- if (error)
- return ERR_PTR(error);
-
- if (unlikely(IS_DEADDIR(parent->d_inode)))
- dentry = ERR_PTR(-ENOENT);
- else
- dentry = lookup_one_len(name, parent, strlen(name));
-
- if (!IS_ERR(dentry) && dentry->d_inode) {
- dput(dentry);
- dentry = ERR_PTR(-EEXIST);
- }
-
- if (IS_ERR(dentry))
- simple_release_fs(&tracefs_mount, &tracefs_mount_count);
-
- return dentry;
-}
-
-/**
- * eventfs_failed_creating - clean up a failed eventfs dentry creation
- * @dentry: The dentry to clean up
- *
- * If after calling eventfs_start_creating(), a failure is detected, the
- * resources created by eventfs_start_creating() needs to be cleaned up. In
- * that case, this function should be called to perform that clean up.
- */
-struct dentry *eventfs_failed_creating(struct dentry *dentry)
-{
- dput(dentry);
- simple_release_fs(&tracefs_mount, &tracefs_mount_count);
- return NULL;
-}
-
-/**
- * eventfs_end_creating - Finish the process of creating a eventfs dentry
- * @dentry: The dentry that has successfully been created.
- *
- * This function is currently just a place holder to match
- * eventfs_start_creating(). In case any synchronization needs to be added,
- * this function will be used to implement that without having to modify
- * the callers of eventfs_start_creating().
- */
-struct dentry *eventfs_end_creating(struct dentry *dentry)
-{
- return dentry;
-}
-
/* Find the inode that this will use for default */
static struct inode *instance_inode(struct dentry *parent, struct inode *inode)
{
@@ -788,6 +717,7 @@ static void init_once(void *foo)
{
struct tracefs_inode *ti = (struct tracefs_inode *) foo;

+ memset(ti, 0, sizeof(*ti));
inode_init_once(&ti->vfs_inode);
}

diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index d4194466b643..ca1ccc86986f 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -46,6 +46,7 @@ struct eventfs_inode {
struct kref kref;
struct list_head list;
const struct eventfs_entry *entries;
+ const char *name;
struct list_head children;
struct dentry *events_dir;
struct eventfs_attr *entry_attrs;
@@ -64,7 +65,6 @@ struct eventfs_inode {
struct llist_node llist;
struct rcu_head rcu;
};
- const char name[];
};

static inline struct tracefs_inode *get_tracefs(const struct inode *inode)
@@ -76,9 +76,6 @@ struct dentry *tracefs_start_creating(const char *name, struct dentry *parent);
struct dentry *tracefs_end_creating(struct dentry *dentry);
struct dentry *tracefs_failed_creating(struct dentry *dentry);
struct inode *tracefs_get_inode(struct super_block *sb);
-struct dentry *eventfs_start_creating(const char *name, struct dentry *parent);
-struct dentry *eventfs_failed_creating(struct dentry *dentry);
-struct dentry *eventfs_end_creating(struct dentry *dentry);

void eventfs_d_release(struct dentry *dentry);