linux-kernel - [RFC 14/19] mm/mlock: add API specification for munlockall

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Message-Id: <20250614134858.790460-15-sashal@kernel.org>
Date: Sat, 14 Jun 2025 09:48:53 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: linux-api@...r.kernel.org,
	workflows@...r.kernel.org,
	tools@...nel.org,
	Sasha Levin <sashal@...nel.org>
Subject: [RFC 14/19] mm/mlock: add API specification for munlockall

Add kernel API specification for the munlockall() system call.

Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 mm/mlock.c | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)

diff --git a/mm/mlock.c b/mm/mlock.c
index ef691adc78ad7..80f51e932aa95 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -1299,6 +1299,126 @@ SYSCALL_DEFINE1(mlockall, int, flags)
 	return ret;
 }
 
+
+DEFINE_KERNEL_API_SPEC(sys_munlockall)
+	KAPI_DESCRIPTION("Unlock all process pages")
+	KAPI_LONG_DESC("Unlocks all pages mapped into the process address space and "
+		       "clears the MCL_FUTURE flag if set.")
+	KAPI_CONTEXT(KAPI_CTX_PROCESS | KAPI_CTX_SLEEPABLE)
+
+	/* No parameters - this is a SYSCALL_DEFINE0 */
+	.param_count = 0,
+
+	/* Return specification */
+	KAPI_RETURN("long", "0 on success, negative error code on failure")
+		.type = KAPI_TYPE_INT,
+		.check_type = KAPI_RETURN_ERROR_CHECK,
+		.success_value = 0,
+	KAPI_RETURN_END
+
+	/* Error codes */
+	KAPI_ERROR(0, -EINTR, "EINTR", "Interrupted by signal", "The operation was interrupted by a signal before completion.")
+	KAPI_ERROR(1, -ENOMEM, "ENOMEM", "Memory operation failed", "Failed to modify memory mappings (should not normally occur).")
+
+	/* Signal specifications */
+	KAPI_SIGNAL(0, 0, "FATAL_SIGNALS", KAPI_SIGNAL_RECEIVE, KAPI_SIGNAL_ACTION_RETURN)
+		KAPI_SIGNAL_CONDITION("Fatal signal pending during mmap_write_lock_killable")
+		KAPI_SIGNAL_DESC("Fatal signals (SIGKILL, SIGTERM, etc.) can interrupt the operation when acquiring mmap_write_lock_killable(), causing -EINTR return")
+		KAPI_SIGNAL_RESTARTABLE
+	KAPI_SIGNAL_END
+
+	/* Side effects */
+	KAPI_SIDE_EFFECT(0, KAPI_EFFECT_MODIFY_STATE,
+			 "all process memory",
+			 "Unlocks all pages, making entire address space swappable")
+		KAPI_EFFECT_REVERSIBLE
+		KAPI_EFFECT_CONDITION("Process had locked pages")
+	KAPI_SIDE_EFFECT_END
+
+	KAPI_SIDE_EFFECT(1, KAPI_EFFECT_MODIFY_STATE,
+			 "mm->def_flags",
+			 "Clears VM_LOCKED from default flags for future mappings")
+		KAPI_EFFECT_REVERSIBLE
+		KAPI_EFFECT_CONDITION("MCL_FUTURE was previously set")
+	KAPI_SIDE_EFFECT_END
+
+	KAPI_SIDE_EFFECT(2, KAPI_EFFECT_MODIFY_STATE,
+			 "mm->locked_vm",
+			 "Resets process locked memory counter to zero")
+		KAPI_EFFECT_REVERSIBLE
+	KAPI_SIDE_EFFECT_END
+
+	KAPI_SIDE_EFFECT(3, KAPI_EFFECT_MODIFY_STATE,
+			 "all VMA flags",
+			 "Clears VM_LOCKED and VM_LOCKONFAULT from all VMAs")
+		KAPI_EFFECT_REVERSIBLE
+	KAPI_SIDE_EFFECT_END
+
+	KAPI_SIDE_EFFECT(4, KAPI_EFFECT_MODIFY_STATE,
+			 "page flags",
+			 "Clears PG_mlocked flag from all locked pages")
+		KAPI_EFFECT_CONDITION("Pages had PG_mlocked set")
+	KAPI_SIDE_EFFECT_END
+
+	KAPI_SIDE_EFFECT(5, KAPI_EFFECT_MODIFY_STATE,
+			 "LRU lists",
+			 "Moves all pages from unevictable to normal LRU lists")
+		KAPI_EFFECT_CONDITION("Pages were on unevictable list")
+	KAPI_SIDE_EFFECT_END
+
+	/* State transitions */
+	KAPI_STATE_TRANS(0, "all memory pages",
+			 "locked in RAM", "swappable",
+			 "All pages in process become eligible for swap out")
+	KAPI_STATE_TRANS_END
+
+	KAPI_STATE_TRANS(1, "future mappings",
+			 "auto-locked", "normal",
+			 "New mappings will no longer be automatically locked")
+		KAPI_STATE_TRANS_COND("MCL_FUTURE was set")
+	KAPI_STATE_TRANS_END
+
+	KAPI_STATE_TRANS(2, "all VMA flags",
+			 "VM_LOCKED set", "VM_LOCKED cleared",
+			 "All virtual memory areas no longer marked as locked")
+	KAPI_STATE_TRANS_END
+
+	KAPI_STATE_TRANS(3, "process statistics",
+			 "all memory locked", "no memory locked",
+			 "Entire locked memory accounting reset to zero")
+	KAPI_STATE_TRANS_END
+
+	KAPI_STATE_TRANS(4, "page LRU status",
+			 "unevictable list", "active/inactive list",
+			 "All pages moved to normal LRU lists for reclaim")
+		KAPI_STATE_TRANS_COND("Pages were mlocked")
+	KAPI_STATE_TRANS_END
+
+	/* Locking information */
+	KAPI_LOCK(0, "mmap_lock", KAPI_LOCK_RWLOCK)
+		KAPI_LOCK_DESC("Process memory map write lock")
+		KAPI_LOCK_ACQUIRED
+		KAPI_LOCK_RELEASED
+		KAPI_LOCK_DESC("Protects VMA modifications during munlockall operation")
+	KAPI_LOCK_END
+
+	KAPI_LOCK(1, "lru_lock", KAPI_LOCK_SPINLOCK)
+		KAPI_LOCK_DESC("Per-memcg LRU list lock")
+		KAPI_LOCK_ACQUIRED
+		KAPI_LOCK_RELEASED
+		KAPI_LOCK_DESC("Taken when moving all pages from unevictable to normal LRU lists")
+	KAPI_LOCK_END
+
+	.error_count = 2,
+	.since_version = "2.0",
+	.signal_count = 1,
+	.side_effect_count = 6,
+	.state_trans_count = 5,
+	.lock_count = 2,
+	.examples = "munlockall();  // Unlock all pages",
+	.notes = "Clears VM_LOCKED and VM_LOCKONFAULT from all VMAs and mm->def_flags",
+KAPI_END_SPEC;
+
 SYSCALL_DEFINE0(munlockall)
 {
 	int ret;
-- 
2.39.5