Re: KCSAN: data-race in __d_drop / retain_dentry

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Mar 11, 2026 at 04:02:41PM +0800, Jianzhou Zhao wrote:

> Execution Flow & Code Context
> When a dentry receives its final decrement during a path operation (e.g., inside `dput`), its lifecycle might traverse `__dentry_kill()` leading to `__d_drop()`. Here, VFS manually eradicates the dentry from the hash list by assigning `NULL` to the internal double-linked list pointer tracker `pprev`:
> ```c
> // fs/dcache.c
> void __d_drop(struct dentry *dentry)
> {
> 	if (!d_unhashed(dentry)) {
> 		___d_drop(dentry);
> 		...
> 		dentry->d_hash.pprev = NULL; // <-- Plain concurrent write
> 		write_seqcount_invalidate(&dentry->d_seq);
> 	}
> }
> ```
> 
> Simultaneously, another thread undergoing an optimistic lockless `dput`

Without having held the reference it's dropping?