Re: [PATCH v2] eventfs: Test for ei->is_freed when accessing ei->dentry

[Steven Rostedt]

On Mon, 30 Oct 2023 12:37:08 +0530
Naresh Kamboju <naresh.kamb...@linaro.org> wrote:

> 
> I have tested the linux-trace.git trace/core and run selftests ftrace
> the reported kernel panic [1] & [2] has been fixed but found

Good to know. Can I add "Tested-by" from you for that bug fix?

> "general protection fault"  at  kernel/trace/trace_events.c:2439.

Can you test with the below patch?

Also, can I ask what are you testing this on that makes it trigger so
easily? As I'm not able to trigger these in my tests, even though they are
indeed bugs.

-- Steve

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 7ad7496bd597..7a0b54ddda24 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -609,7 +609,13 @@ static struct dentry *eventfs_root_lookup(struct inode 
*dir,
                entry = &ei->entries[i];
                if (strcmp(name, entry->name) == 0) {
                        void *cdata = data;
-                       r = entry->callback(name, &mode, &cdata, &fops);
+                       mutex_lock(&eventfs_mutex);
+                       /* If ei->is_freed, then the event itself may be too */
+                       if (!ei->is_freed)
+                               r = entry->callback(name, &mode, &cdata, &fops);
+                       else
+                               r = -1;
+                       mutex_unlock(&eventfs_mutex);
                        if (r <= 0)
                                continue;
                        ret = simple_lookup(dir, dentry, flags);
@@ -743,7 +749,13 @@ static int dcache_dir_open_wrapper(struct inode *inode, 
struct file *file)
                void *cdata = data;
                entry = &ei->entries[i];
                name = entry->name;
-               r = entry->callback(name, &mode, &cdata, &fops);
+               mutex_lock(&eventfs_mutex);
+               /* If ei->is_freed, then the event itself may be too */
+               if (!ei->is_freed)
+                       r = entry->callback(name, &mode, &cdata, &fops);
+               else
+                       r = -1;
+               mutex_unlock(&eventfs_mutex);
                if (r <= 0)
                        continue;
                d = create_file_dentry(ei, i, parent, name, mode, cdata, fops, 
false);