x86/intel_rdt/cqm: Prevent use after free

intel_rdt_iffline_cpu() -> domain_remove_cpu() frees memory first and then
proceeds accessing it.

 BUG: KASAN: use-after-free in find_first_bit+0x1f/0x80
 Read of size 8 at addr ffff883ff7c1e780 by task cpuhp/31/195
 find_first_bit+0x1f/0x80
 has_busy_rmid+0x47/0x70
 intel_rdt_offline_cpu+0x4b4/0x510

 Freed by task 195:
 kfree+0x94/0x1a0
 intel_rdt_offline_cpu+0x17d/0x510

Do the teardown first and then free memory.

Fixes: 24247aee ("x86/intel_rdt/cqm: Improve limbo list processing")
Reported-by: NJoseph Salisbury <joseph.salisbury@canonical.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Ravi Shankar <ravi.v.shankar@intel.com>
Cc: Peter Zilstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "Roderick W. Smith" <rod.smith@canonical.com>
Cc: 1733662@bugs.launchpad.net
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801161957510.2366@nanos

arch/x86/kernel/cpu/intel_rdt.c

@@ -525,10 +525,6 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 		 */
 		if (static_branch_unlikely(&rdt_mon_enable_key))
 			rmdir_mondata_subdir_allrdtgrp(r, d->id);
-		kfree(d->ctrl_val);
-		kfree(d->rmid_busy_llc);
-		kfree(d->mbm_total);
-		kfree(d->mbm_local);
 		list_del(&d->list);
 		if (is_mbm_enabled())
 			cancel_delayed_work(&d->mbm_over);
@@ -545,6 +541,10 @@ static void domain_remove_cpu(int cpu, struct rdt_resource *r)
 			cancel_delayed_work(&d->cqm_limbo);
 		}
 
+		kfree(d->ctrl_val);
+		kfree(d->rmid_busy_llc);
+		kfree(d->mbm_total);
+		kfree(d->mbm_local);
 		kfree(d);
 		return;
 	}