[PATCH] x86/intel_rdt: Put group node in rdtgroup_kn_unlock

[Jiri Olsa]

The rdtgroup_kn_unlock waits for the last user to release
and put its node. But it's calling kernfs_put on the node
which calls the rdtgroup_kn_unlock, which might not be
the group's directory node, but another group's file node.

This race could be easily reproduced by running 2 instances
of following script:

  mount -t resctrl resctrl /sys/fs/resctrl/
  pushd /sys/fs/resctrl/
  mkdir krava
  echo "krava" > krava/schemata
  rmdir krava
  popd
  umount  /sys/fs/resctrl

It triggers the slub debug error message with following command
line config: slub_debug=,kernfs_node_cache.

Calling kernfs_put on the group's node.

Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c 
b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index c05509d38b1f..9ac2a5cdd9c2 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -727,7 +727,7 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
        if (atomic_dec_and_test(&rdtgrp->waitcount) &&
            (rdtgrp->flags & RDT_DELETED)) {
                kernfs_unbreak_active_protection(kn);
-               kernfs_put(kn);
+               kernfs_put(rdtgrp->kn);
                kfree(rdtgrp);
        } else {
                kernfs_unbreak_active_protection(kn);
-- 
2.9.3