sched/membarrier: Introduce MEMBARRIER_CMD_GET_REGISTRATIONS

Provide a method to query previously issued registrations.

Signed-off-by: Michal Clapinski <mclapinski@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20221207164338.1535591-2-mclapinski@google.com

diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h
index 7376058..5f3ad6d 100644 (file)
--- a/include/uapi/linux/membarrier.h
+++ b/include/uapi/linux/membarrier.h
@@ -137,6 +137,9 @@
  * @MEMBARRIER_CMD_SHARED:
  *                          Alias to MEMBARRIER_CMD_GLOBAL. Provided for
  *                          header backward compatibility.
+ * @MEMBARRIER_CMD_GET_REGISTRATIONS:
+ *                          Returns a bitmask of previously issued
+ *                          registration commands.
  *
  * Command to be passed to the membarrier system call. The commands need to
  * be a single bit each, except for MEMBARRIER_CMD_QUERY which is assigned to
@@ -153,6 +156,7 @@ enum membarrier_cmd {
        MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE     = (1 << 6),
        MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ                   = (1 << 7),
        MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ          = (1 << 8),
+       MEMBARRIER_CMD_GET_REGISTRATIONS                        = (1 << 9),
 
        /* Alias for header backward compatibility. */
        MEMBARRIER_CMD_SHARED                   = MEMBARRIER_CMD_GLOBAL,

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 0c5be7e..2ad881d 100644 (file)
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -159,7 +159,8 @@
        | MEMBARRIER_CMD_PRIVATE_EXPEDITED                              \
        | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED                     \
        | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK                \
-       | MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK)
+       | MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK                     \
+       | MEMBARRIER_CMD_GET_REGISTRATIONS)
 
 static void ipi_mb(void *info)
 {
@@ -540,6 +541,40 @@ static int membarrier_register_private_expedited(int flags)
        return 0;
 }
 
+static int membarrier_get_registrations(void)
+{
+       struct task_struct *p = current;
+       struct mm_struct *mm = p->mm;
+       int registrations_mask = 0, membarrier_state, i;
+       static const int states[] = {
+               MEMBARRIER_STATE_GLOBAL_EXPEDITED |
+                       MEMBARRIER_STATE_GLOBAL_EXPEDITED_READY,
+               MEMBARRIER_STATE_PRIVATE_EXPEDITED |
+                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_READY,
+               MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE |
+                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_SYNC_CORE_READY,
+               MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ |
+                       MEMBARRIER_STATE_PRIVATE_EXPEDITED_RSEQ_READY
+       };
+       static const int registration_cmds[] = {
+               MEMBARRIER_CMD_REGISTER_GLOBAL_EXPEDITED,
+               MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED,
+               MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_SYNC_CORE,
+               MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ
+       };
+       BUILD_BUG_ON(ARRAY_SIZE(states) != ARRAY_SIZE(registration_cmds));
+
+       membarrier_state = atomic_read(&mm->membarrier_state);
+       for (i = 0; i < ARRAY_SIZE(states); ++i) {
+               if (membarrier_state & states[i]) {
+                       registrations_mask |= registration_cmds[i];
+                       membarrier_state &= ~states[i];
+               }
+       }
+       WARN_ON_ONCE(membarrier_state != 0);
+       return registrations_mask;
+}
+
 /**
  * sys_membarrier - issue memory barriers on a set of threads
  * @cmd:    Takes command values defined in enum membarrier_cmd.
@@ -623,6 +658,8 @@ SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id)
                return membarrier_private_expedited(MEMBARRIER_FLAG_RSEQ, cpu_id);
        case MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED_RSEQ:
                return membarrier_register_private_expedited(MEMBARRIER_FLAG_RSEQ);
+       case MEMBARRIER_CMD_GET_REGISTRATIONS:
+               return membarrier_get_registrations();
        default:
                return -EINVAL;
        }