Re: [PATCH 0/4] kernfs: remove kernfs_rwsem from dentry revalidation

[Ian Kent]

On 25/8/26 22:58, Christian Brauner wrote:
> On Thu, 20 Aug 2026 22:05:03 -0700, Shakeel Butt wrote:
> > kernfs: remove kernfs_rwsem from dentry revalidation
> >
> > At Meta, we are seeing important system daemons that poll cgroupfs and
> > sysfs geth stuck in kernfs_dop_revalidate() for minutes. The two that
> > hurt most are the ones we can least afford to lose: oomd, which decides
> > what to kill when a machine runs out of memory, and below[1], which
> > records the telemetry used to understand what happened afterwards.
> >
> > [...]
> Applied to the vfs-7.4.kernfs branch of the vfs/vfs.git tree.
> Patches in the vfs-7.4.kernfs branch should appear in linux-next soon.
>
> Please report any outstanding bugs that were missed during review in a
> new review to the original patch series allowing us to drop it.
>
> It's encouraged to provide Acked-bys and Reviewed-bys even though the
> patch has now been applied. If possible patch trailers will be updated.


I have a report against kernfs where I cannot find a reason for significant

contention, primarily on ->revaliate(), in either of two vmcores, exactly

the case described in this series.


I reviewed the series and it looks good to me.

The descriptions justifying the changes also look sound.


While I think renames and removals should be ok based on the descriptions

justifying the change (my biggest concern with removing the rwsem) I'll

continue to ponder its implications for a while.


Reviewed-by: Ian Kent <raven@xxxxxxxxxx>


> Note that commit hashes shown below are subject to change due to rebase,
> trailer updates or similar. If in doubt, please check the listed branch.
>
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> branch: vfs-7.4.kernfs
>
> [1/4] kernfs: Use VFS lookup context in d_revalidate()
>        https://git.kernel.org/vfs/vfs/c/b3c97f5cb084
> [2/4] kernfs: Prepare directory revisions for lockless reads
>        https://git.kernel.org/vfs/vfs/c/272e0997df44
> [3/4] kernfs: Avoid namespace dereference in d_revalidate()
>        https://git.kernel.org/vfs/vfs/c/e1c629a8dbc7
> [4/4] kernfs: Remove kernfs_rwsem from dentry revalidation
>        https://git.kernel.org/vfs/vfs/c/8c6ad578e2f0