Re: [PATCH v3 4/9] fs/resctrl: Fix deadlock for errors during mount

[Ben Horgan <ben.horgan@arm.com>]

Hi Reinette,

On 5/22/26 20:15, Reinette Chatre wrote:
> rdt_get_tree() acquires rdtgroup_mutex before calling kernfs_get_tree(). If
> superblock setup fails inside kernfs_get_tree(), the VFS calls kill_sb on
> the same thread before the call returns.  rdt_kill_sb() unconditionally
> attempts to acquire rdtgroup_mutex and deadlock occurs.
> 
> Move the call to kernfs_get_tree() outside of locks. If kernfs_get_tree()
> fails and ctx->kfc.new_sb_created is set, then rdt_kill_sb() has already
> been called and no further cleanup is needed.
> 
> Add an extra hold in this error path on rdtgroup_default.kn to defend against
> other races destroying the root which is then dereferenced in kernfs_kill_sb()
> 
> Add resctrl_unmount() helper to keep code consistent between the
> rdt_get_tree() failure path and a normal unmount.
> 
> Fixes: 5ff193fbde20 ("x86/intel_rdt: Add basic resctrl filesystem support")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://sashiko.dev/#/patchset/20260429184858.36423-1-tony.luck%40intel.com [1]
> Co-developed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>

Looks good to me.

Reviewed-by: Ben Horgan <ben.horgan@arm.com>

Thanks,

Ben