On Fri, Jan 31, 2025 at 04:03:27PM +0000, Jean-SébastienPédron wrote:
> The branch main has been updated by dumbbell:
>
> URL:
> https://cgit.FreeBSD.org/src/commit/?id=e5764cf0758855e2d5a9ebab6d6addc6eaccd56e
>
> commit e5764cf0758855e2d5a9ebab6d6addc6eaccd56e
> Author: Jean-Sébastien Pédron <dumbb...@freebsd.org>
> AuthorDate: 2025-01-21 22:54:51 +0000
> Commit: Jean-Sébastien Pédron <dumbb...@freebsd.org>
> CommitDate: 2025-01-31 16:00:50 +0000
>
> linuxkpi: Don't destroy the mutex in `xa_destroy()`
>
> [Why]
> The mutex initialized in `xa_init_flags()` is not destroyed here on
> purpose. The reason is that on Linux, the xarray remains usable after a
> call to `xa_destroy()`. For instance the i915 DRM driver relies on that
> during the initialixation of its GuC. Basically, `xa_destroy()` "resets"
> the structure to zero but doesn't really destroy it.
>
> Reviewed by: manu
> Sponsored by: The FreeBSD Foundation
> Differential Revision: https://reviews.freebsd.org/D48762
> ---
> sys/compat/linuxkpi/common/src/linux_xarray.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/sys/compat/linuxkpi/common/src/linux_xarray.c
> b/sys/compat/linuxkpi/common/src/linux_xarray.c
> index 54c536042392..3f07f6d7c59f 100644
> --- a/sys/compat/linuxkpi/common/src/linux_xarray.c
> +++ b/sys/compat/linuxkpi/common/src/linux_xarray.c
> @@ -362,9 +362,19 @@ xa_destroy(struct xarray *xa)
> struct radix_tree_iter iter;
> void **ppslot;
>
> + xa_lock(xa);
> radix_tree_for_each_slot(ppslot, &xa->xa_head, &iter, 0)
> radix_tree_iter_delete(&xa->xa_head, &iter, ppslot);
> - mtx_destroy(&xa->xa_lock);
> + xa_unlock(xa);
> +
> + /*
> + * The mutex initialized in `xa_init_flags()` is not destroyed here on
> + * purpose. The reason is that on Linux, the xarray remains usable
> + * after a call to `xa_destroy()`. For instance the i915 DRM driver
> + * relies on that during the initialixation of its GuC. Basically,
> + * `xa_destroy()` "resets" the structure to zero but doesn't really
> + * destroy it.
> + */
> }
>
> /*
Was this tested with WITNESS and unloading a module that created xarray?
I suspect this situation should result in panic/page fault.
