[PATCH 1/3] x86/intel_rdt: Fix kernfs_to_rdtgroup to know about "info/*" directories

[Fenghua Yu]

From: Fenghua Yu <fenghua...@intel.com>

We saw a kernel oops on NULL pointer when we ran "rmdir info". This is
because the "info" directory and per-resource subdirectories of "info"
do not use "kn->priv" to point to a "struct rdtgroup".

Also change error code from -ENOENT to the more appropriate -EPERM
so the user sees "Operation not permitted".

Signed-off-by: Fenghua Yu <fenghua...@intel.com>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c 
b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index 4795880..cff286e 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -644,16 +644,29 @@ static int parse_rdtgroupfs_options(char *data)
  */
 static struct rdtgroup *kernfs_to_rdtgroup(struct kernfs_node *kn)
 {
-       if (kernfs_type(kn) == KERNFS_DIR)
-               return kn->priv;
-       else
+       if (kernfs_type(kn) == KERNFS_DIR) {
+               /*
+                * All the resource directories use "kn->priv"
+                * to point to the "struct rdtgroup" for the
+                * resource. "info" and its subdirectories don't
+                * have rdtgroup structures, so return NULL here.
+                */
+               if (kn == kn_info || kn->parent == kn_info)
+                       return NULL;
+               else
+                       return kn->priv;
+       } else {
                return kn->parent->priv;
+       }
 }
 
 struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn)
 {
        struct rdtgroup *rdtgrp = kernfs_to_rdtgroup(kn);
 
+       if (!rdtgrp)
+               return NULL;
+
        atomic_inc(&rdtgrp->waitcount);
        kernfs_break_active_protection(kn);
 
@@ -670,6 +683,9 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
 {
        struct rdtgroup *rdtgrp = kernfs_to_rdtgroup(kn);
 
+       if (!rdtgrp)
+               return;
+
        mutex_unlock(&rdtgroup_mutex);
 
        if (atomic_dec_and_test(&rdtgrp->waitcount) &&
@@ -918,7 +934,7 @@ static int rdtgroup_rmdir(struct kernfs_node *kn)
        rdtgrp = rdtgroup_kn_lock_live(kn);
        if (!rdtgrp) {
                rdtgroup_kn_unlock(kn);
-               return -ENOENT;
+               return -EPERM;
        }
 
        /* Give any tasks back to the default group */
-- 
2.5.0