Re: [PATCH v3 tip/perf/core 4/4] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution

On Wed, Oct 23, 2024 at 01:02:53PM -0700, Andrii Nakryiko wrote:

quoted

quoted

+      * but can't be freed from under us, so it's safe to read fields from
+      * it, even if the values are some garbage values; ultimately
+      * find_uprobe_rcu() + mmap_lock_speculation_end() check will ensure
+      * that whatever we speculatively found is correct
+      */
+     vm_file = READ_ONCE(vma->vm_file);
+     if (!vm_file)
+             return NULL;
+
+     vm_pgoff = data_race(vma->vm_pgoff);
+     vm_start = data_race(vma->vm_start);
+     vm_inode = data_race(vm_file->f_inode);

So... seqcount has kcsan annotations other than data_race(). I suppose
this works, but it all feels like a bad copy with random changes.

I'm not sure what this means... Do I need to change anything? Drop
data_race()? Use READ_ONCE()? Do nothing?

Keep for now. I've ranted at 1/n a bit, but unless the response is:
yeah, obviously this should be seqcount (unlikely) this is something
that can be fixed later (*sigh* always later... this todo list is a
problem).