Re: [PATCH 1/3] kernfs: don't repeat or skip an entry when readdir resumes

[Tejun Heo <tj@kernel.org>]

On Wed, Sep 09, 2026 at 05:36:48PM -0700, Shakeel Butt wrote:
> readdir keeps its place as a name hash in ctx->pos and pins the entry in
> file->private_data.  If that entry is gone when the listing comes back,
> kernfs_dir_pos() searches the rbtree for the hash and keeps whatever
> node the descent stopped on.  That is the entry before or after the
> missing one, depending on the shape of the tree.
> 
> Landing before it repeats an entry the previous getdents(2) call already
> reported.  Landing after it, kernfs_dir_next_pos() calls rb_next() and
> steps over an unreported entry.
> 
> With children A(10), B(20), C(30):
> 
>   report A, ctx->pos = 10
>                                     A removed
>   kernfs_dir_next_pos(10, A)
>     A is gone, the search for 10 stops at B
>     rb_next(B) -> C, so B is never reported
> 
> Only the repeat happens today, between two getdents(2) calls.  The skip
> needs the pinned entry to go away inside one call, which the next patch
> allows when it drops kernfs_rwsem around dir_emit().
> 
> Before the commit 4e4d6d860b93 the descent kept a node only on the way
> left, which is a search for the first entry at or after the hash.  That
> commit moved the assignment to the top of the loop, where it runs on
> right turns too.  Restore that search, and step forward only when the
> pinned entry is still there rather than when the hash matches, since two
> entries in one directory can share a hash.
> 
> While here, kernfs_dir_next_pos() called the hash @ino.  It is never an
> inode number, so name it @hash.
> 
> Fixes: 4e4d6d860b93 ("sysfs: Add s_hash to sysfs_dirent and order directory entries by hash")
> Assisted-by: LLM
> Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun