x86/intel_rdt: Provide pseudo-locking hooks within rdt_mount

Stephen Rothwell reported that the Cache Pseudo-Locking enabling and the
kernfs support for mounting with fs_context are conflicting.

In preparation for a conflict-free merge between the two repos some no-op
hooks are created within the RDT mount function being changed by the two
features. The goal is for this commit to be placed on a minimal no-rebase
branch to be consumed by both features.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Suggested-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Cc: David Howells <dhowells@redhat.com>
Link: https://lkml.kernel.org/r/410697ead08978bd12111c0afc4ce9e7bd71a5fe.1529706536.git.reinette.chatre@intel.com

arch/x86/kernel/cpu/intel_rdt.h

@@ -468,4 +468,13 @@ void cqm_handle_limbo(struct work_struct *work);
 bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d);
 void __check_limbo(struct rdt_domain *d, bool force_free);
 
+/*
+ * Define the hooks for Cache Pseudo-Locking to use within rdt_mount().
+ * These are no-ops provided for the new kernfs changes to use as a
+ * baseline in preparation for a conflict-free merge between it
+ * (kernfs changes) and the Cache Pseudo-Locking enabling.
+ */
+static inline int rdt_pseudo_lock_init(void) { return 0; }
+static inline void rdt_pseudo_lock_release(void) { }
+
 #endif /* _ASM_X86_INTEL_RDT_H */

arch/x86/kernel/cpu/intel_rdt_rdtgroup.c

@@ -1289,10 +1289,16 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
 		rdtgroup_default.mon.mon_data_kn = kn_mondata;
 	}
 
+	ret = rdt_pseudo_lock_init();
+	if (ret) {
+		dentry = ERR_PTR(ret);
+		goto out_mondata;
+	}
+
 	dentry = kernfs_mount(fs_type, flags, rdt_root,
 			      RDTGROUP_SUPER_MAGIC, NULL);
 	if (IS_ERR(dentry))
-		goto out_mondata;
+		goto out_psl;
 
 	if (rdt_alloc_capable)
 		static_branch_enable_cpuslocked(&rdt_alloc_enable_key);
@@ -1310,6 +1316,8 @@ static struct dentry *rdt_mount(struct file_system_type *fs_type,
 
 	goto out;
 
+out_psl:
+	rdt_pseudo_lock_release();
 out_mondata:
 	if (rdt_mon_capable)
 		kernfs_remove(kn_mondata);