mm: add account_locked_vm utility function

locked_vm accounting is done roughly the same way in five places, so
unify them in a helper.

Include the helper's caller in the debug print to distinguish between
callsites.

Error codes stay the same, so user-visible behavior does too.  The one
exception is that the -EPERM case in tce_account_locked_vm is removed
because Alexey has never seen it triggered.

[[email protected]: v3]
  Link: http://lkml.kernel.org/r/[email protected]
[[email protected]: fix mm/util.c]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Daniel Jordan <[email protected]>
Signed-off-by: Stephen Rothwell <[email protected]>
Tested-by: Alexey Kardashevskiy <[email protected]>
Acked-by: Alex Williamson <[email protected]>
Cc: Alan Tull <[email protected]>
Cc: Alex Williamson <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Moritz Fischer <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Steve Sistare <[email protected]>
Cc: Wu Hao <[email protected]>
Cc: Ira Weiny <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/util.c

@@ -7,6 +7,7 @@
 #include <linux/err.h>
 #include <linux/sched.h>
 #include <linux/sched/mm.h>
+#include <linux/sched/signal.h>
 #include <linux/sched/task_stack.h>
 #include <linux/security.h>
 #include <linux/swap.h>
@@ -300,6 +301,80 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 }
 #endif
 
+/**
+ * __account_locked_vm - account locked pages to an mm's locked_vm
+ * @mm:          mm to account against
+ * @pages:       number of pages to account
+ * @inc:         %true if @pages should be considered positive, %false if not
+ * @task:        task used to check RLIMIT_MEMLOCK
+ * @bypass_rlim: %true if checking RLIMIT_MEMLOCK should be skipped
+ *
+ * Assumes @task and @mm are valid (i.e. at least one reference on each), and
+ * that mmap_sem is held as writer.
+ *
+ * Return:
+ * * 0       on success
+ * * -ENOMEM if RLIMIT_MEMLOCK would be exceeded.
+ */
+int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
+			struct task_struct *task, bool bypass_rlim)
+{
+	unsigned long locked_vm, limit;
+	int ret = 0;
+
+	lockdep_assert_held_write(&mm->mmap_sem);
+
+	locked_vm = mm->locked_vm;
+	if (inc) {
+		if (!bypass_rlim) {
+			limit = task_rlimit(task, RLIMIT_MEMLOCK) >> PAGE_SHIFT;
+			if (locked_vm + pages > limit)
+				ret = -ENOMEM;
+		}
+		if (!ret)
+			mm->locked_vm = locked_vm + pages;
+	} else {
+		WARN_ON_ONCE(pages > locked_vm);
+		mm->locked_vm = locked_vm - pages;
+	}
+
+	pr_debug("%s: [%d] caller %ps %c%lu %lu/%lu%s\n", __func__, task->pid,
+		 (void *)_RET_IP_, (inc) ? '+' : '-', pages << PAGE_SHIFT,
+		 locked_vm << PAGE_SHIFT, task_rlimit(task, RLIMIT_MEMLOCK),
+		 ret ? " - exceeded" : "");
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(__account_locked_vm);
+
+/**
+ * account_locked_vm - account locked pages to an mm's locked_vm
+ * @mm:          mm to account against, may be NULL
+ * @pages:       number of pages to account
+ * @inc:         %true if @pages should be considered positive, %false if not
+ *
+ * Assumes a non-NULL @mm is valid (i.e. at least one reference on it).
+ *
+ * Return:
+ * * 0       on success, or if mm is NULL
+ * * -ENOMEM if RLIMIT_MEMLOCK would be exceeded.
+ */
+int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc)
+{
+	int ret;
+
+	if (pages == 0 || !mm)
+		return 0;
+
+	down_write(&mm->mmap_sem);
+	ret = __account_locked_vm(mm, pages, inc, current,
+				  capable(CAP_IPC_LOCK));
+	up_write(&mm->mmap_sem);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(account_locked_vm);
+
 unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
 	unsigned long len, unsigned long prot,
 	unsigned long flag, unsigned long pgoff)