x86/intel_rdt: Put group node in rdtgroup_kn_unlock

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.

Call kernfs_put on the group's node to fix it.

Fixes: 60cf5e101fd4 ("x86/intel_rdt: Add mkdir to resctrl file system")
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Shaohua Li <shli@fb.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1489501253-20248-1-git-send-email-jolsa@kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index c05509d38b1f1e5ed0f63940dc2c8496b360b032..9ac2a5cdd9c206e83f171847ac04d5bf4f2a3152 100644 (file)
--- 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);