mm/vmap: add DEBUG_AUGMENT_LOWEST_MATCH_CHECK macro

This macro adds some debug code to check that vmap allocations are
happened in ascending order.

By default this option is set to 0 and not active.  It requires
recompilation of the kernel to activate it.  Set to 1, compile the
kernel.

[urezki@gmail.com: v4]
  Link: http://lkml.kernel.org/r/20190406183508.25273-4-urezki@gmail.com
Link: http://lkml.kernel.org/r/20190402162531.10888-4-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -326,6 +326,7 @@ EXPORT_SYMBOL(vmalloc_to_pfn);
 /*** Global kva allocator ***/
 
 #define DEBUG_AUGMENT_PROPAGATE_CHECK 0
+#define DEBUG_AUGMENT_LOWEST_MATCH_CHECK 0
 
 #define VM_LAZY_FREE	0x02
 #define VM_VM_AREA	0x04
@@ -834,6 +835,44 @@ find_vmap_lowest_match(unsigned long size,
 	return NULL;
 }
 
+#if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
+#include <linux/random.h>
+
+static struct vmap_area *
+find_vmap_lowest_linear_match(unsigned long size,
+	unsigned long align, unsigned long vstart)
+{
+	struct vmap_area *va;
+
+	list_for_each_entry(va, &free_vmap_area_list, list) {
+		if (!is_within_this_va(va, size, align, vstart))
+			continue;
+
+		return va;
+	}
+
+	return NULL;
+}
+
+static void
+find_vmap_lowest_match_check(unsigned long size)
+{
+	struct vmap_area *va_1, *va_2;
+	unsigned long vstart;
+	unsigned int rnd;
+
+	get_random_bytes(&rnd, sizeof(rnd));
+	vstart = VMALLOC_START + rnd;
+
+	va_1 = find_vmap_lowest_match(size, 1, vstart);
+	va_2 = find_vmap_lowest_linear_match(size, 1, vstart);
+
+	if (va_1 != va_2)
+		pr_emerg("not lowest: t: 0x%p, l: 0x%p, v: 0x%lx\n",
+			va_1, va_2, vstart);
+}
+#endif
+
 enum fit_type {
 	NOTHING_FIT = 0,
 	FL_FIT_TYPE = 1,	/* full fit */
@@ -976,6 +1015,10 @@ __alloc_vmap_area(unsigned long size, unsigned long align,
 	if (ret)
 		return vend;
 
+#if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
+	find_vmap_lowest_match_check(size);
+#endif
+
 	return nva_start_addr;
 }