x86/shstk: don't unlock shadow stack for zombies

Signed-off-by: Mike Rapoport (IBM) <[email protected]>

criu/arch/x86/shstk.c

@@ -78,12 +78,19 @@ int prepare_shstk(struct pstree_item *item, CoreEntry *core,
 
 int unlock_shstk(struct pstree_item *item, CoreEntry *core, pid_t pid)
 {
-	UserX86FpregsEntry *fpregs = core->thread_info->fpregs;
 	unsigned long features;
 	int status;
 	int ret = 0;
 
+	if (!task_alive(item))
+		goto futex_wake;
+
+	if (!compel_cpu_has_feature(X86_FEATURE_FPU))
+		goto futex_wake;
+
 	if (!compel_cpu_has_feature(X86_FEATURE_SHSTK)) {
+		UserX86FpregsEntry *fpregs = core->thread_info->fpregs;
+
 		if (fpregs->xsave && fpregs->xsave->cet)
 			pr_warn("Restoring task with shadow stack on non-CET machine\n");
 		goto futex_wake;