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Date:   Wed,  7 Dec 2022 17:43:37 +0100
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Subject: [PATCH 1/2] sched/membarrier: Introduce MEMBARRIER_CMD_GET_REGISTRATIONS
From:   Michal Clapinski <mclapinski@google.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@kernel.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrei Vagin <avagin@gmail.com>, Shuah Khan <shuah@kernel.org>,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        Michal Clapinski <mclapinski@google.com>
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Provide a method to query previously issued registrations.

Signed-off-by: Michal Clapinski <mclapinski@google.com>
---
 include/uapi/linux/membarrier.h |  4 ++++
 kernel/sched/membarrier.c       | 39 ++++++++++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/membarrier.h b/include/uapi/linux/membarrier.h
index 737605897f36..5f3ad6d5be6f 100644
--- 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 0c5be7ebb1dc..2ad881d07752 100644
--- 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;
 	}
-- 
2.39.0.rc0.267.gcb52ba06e7-goog