restore: Bring trivial locker back

Threads are better to be restored in serialized
way otherwise if some error happened an error
message will be screwed.
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

cr-restore.c

@@ -1453,6 +1453,7 @@ static void sigreturn_restore(pid_t pstree_pid, pid_t pid)
 	task_args->pid		= pid;
 	task_args->fd_core	= fd_core;
 	task_args->fd_self_vmas	= fd_self_vmas;
+	task_args->rst_lock	= 0;
 
 	if (pstree_entry.nr_threads) {
 		int i;
@@ -1479,6 +1480,8 @@ static void sigreturn_restore(pid_t pstree_pid, pid_t pid)
 				goto err;
 			}
 
+			thread_args[i].rst_lock = &task_args->rst_lock;
+
 			pr_info("Thread %4d stack %8p heap %8p rt_sigframe %8p\n",
 				i, (long)thread_args[i].mem_zone.stack,
 				thread_args[i].mem_zone.heap,

include/restorer.h

@@ -54,6 +54,7 @@ struct thread_restore_args {
 
 	int				pid;
 	int				fd_core;
+	long				*rst_lock;
 } __aligned(sizeof(long));
 
 struct task_restore_core_args {
@@ -63,6 +64,7 @@ struct task_restore_core_args {
 	int				fd_core;		/* opened core file */
 	int				fd_self_vmas;		/* opened file with running VMAs to unmap */
 	bool				restore_threads;	/* if to restore threads */
+	long				rst_lock;
 
 	/* threads restoration */
 	int				nr_threads;		/* number of threads */
@@ -222,4 +224,29 @@ static void always_inline write_hex_n(unsigned long num)
 	sys_write(1, &c, 1);
 }
 
+static always_inline void rst_lock(long *v)
+{
+	while (*v) {
+		asm volatile("lfence");
+		asm volatile("pause");
+	}
+	(*v)++;
+
+	asm volatile("sfence");
+}
+
+static always_inline void rst_unlock(long *v)
+{
+	(*v)--;
+	asm volatile("sfence");
+}
+
+static always_inline void rst_wait_unlock(long *v)
+{
+	while (*v) {
+		asm volatile("lfence");
+		asm volatile("pause");
+	}
+}
+
 #endif /* CR_RESTORER_H__ */

restorer.c

@@ -86,6 +86,8 @@ long restore_thread(long cmd, struct thread_restore_args *args)
 			goto core_restore_end;
 		}
 
+		rst_unlock(args->rst_lock);
+
 		new_sp = (long)rt_sigframe + 8;
 		asm volatile(
 			"movq %0, %%rax					\n"
@@ -428,6 +430,8 @@ self_len_end:
 				if (thread_args[i].pid == args->pid)
 					continue;
 
+				rst_lock(&args->rst_lock);
+
 				new_sp =
 					RESTORE_ALIGN_STACK((long)thread_args[i].mem_zone.stack,
 							    sizeof(thread_args[i].mem_zone.stack));
@@ -478,7 +482,7 @@ self_len_end:
 						"g"(&thread_args[i])
 					: "rax", "rdi", "rsi", "rdx", "r10", "memory");
 
-				//r_wait_unlock(args->lock);
+				rst_wait_unlock(&args->rst_lock);
 			}
 		}