mm: check rb_subtree_gap correctness

When CONFIG_DEBUG_VM_RB is enabled, check that rb_subtree_gap is correctly
set for every vma and that mm->highest_vm_end is also correct.

Also add an explicit 'bug' variable to track if browse_rb() detected any
invalid condition.

[akpm@linux-foundation.org: repair innovative coding-style inventions]
Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 39 insertions, 14 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index bdcea6310fff..ff93f6c8436c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -322,31 +322,45 @@ static long vma_compute_subtree_gap(struct vm_area_struct *vma)
 #ifdef CONFIG_DEBUG_VM_RB
 static int browse_rb(struct rb_root *root)
 {
-        int i = 0, j;
+        int i = 0, j, bug = 0;
         struct rb_node *nd, *pn = NULL;
         unsigned long prev = 0, pend = 0;
 
         for (nd = rb_first(root); nd; nd = rb_next(nd)) {
                 struct vm_area_struct *vma;
                 vma = rb_entry(nd, struct vm_area_struct, vm_rb);
-                if (vma->vm_start < prev)
-                        printk("vm_start %lx prev %lx\n", vma->vm_start, prev), i = -1;
-                if (vma->vm_start < pend)
+                if (vma->vm_start < prev) {
+                        printk("vm_start %lx prev %lx\n", vma->vm_start, prev);
+                        bug = 1;
+                }
+                if (vma->vm_start < pend) {
                         printk("vm_start %lx pend %lx\n", vma->vm_start, pend);
-                if (vma->vm_start > vma->vm_end)
-                        printk("vm_end %lx < vm_start %lx\n", vma->vm_end, vma->vm_start);
+                        bug = 1;
+                }
+                if (vma->vm_start > vma->vm_end) {
+                        printk("vm_end %lx < vm_start %lx\n",
+                                vma->vm_end, vma->vm_start);
+                        bug = 1;
+                }
+                if (vma->rb_subtree_gap != vma_compute_subtree_gap(vma)) {
+                        printk("free gap %lx, correct %lx\n",
+                               vma->rb_subtree_gap,
+                               vma_compute_subtree_gap(vma));
+                        bug = 1;
+                }
                 i++;
                 pn = nd;
                 prev = vma->vm_start;
                 pend = vma->vm_end;
         }
         j = 0;
-        for (nd = pn; nd; nd = rb_prev(nd)) {
+        for (nd = pn; nd; nd = rb_prev(nd))
                 j++;
+        if (i != j) {
+                printk("backwards %d, forwards %d\n", j, i);
+                bug = 1;
         }
-        if (i != j)
-                printk("backwards %d, forwards %d\n", j, i), i = 0;
-        return i;
+        return bug ? -1 : i;
 }
 
 static void validate_mm_rb(struct rb_root *root, struct vm_area_struct *ignore)
@@ -365,6 +379,7 @@ void validate_mm(struct mm_struct *mm)
 {
         int bug = 0;
         int i = 0;
+        unsigned long highest_address = 0;
         struct vm_area_struct *vma = mm->mmap;
         while (vma) {
                 struct anon_vma_chain *avc;
@@ -372,14 +387,24 @@ void validate_mm(struct mm_struct *mm)
                 list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
                         anon_vma_interval_tree_verify(avc);
                 vma_unlock_anon_vma(vma);
+                highest_address = vma->vm_end;
                 vma = vma->vm_next;
                 i++;
         }
-        if (i != mm->map_count)
-                printk("map_count %d vm_next %d\n", mm->map_count, i), bug = 1;
+        if (i != mm->map_count) {
+                printk("map_count %d vm_next %d\n", mm->map_count, i);
+                bug = 1;
+        }
+        if (highest_address != mm->highest_vm_end) {
+                printk("mm->highest_vm_end %lx, found %lx\n",
+                       mm->highest_vm_end, highest_address);
+                bug = 1;
+        }
         i = browse_rb(&mm->mm_rb);
-        if (i != mm->map_count)
-                printk("map_count %d rb %d\n", mm->map_count, i), bug = 1;
+        if (i != mm->map_count) {
+                printk("map_count %d rb %d\n", mm->map_count, i);
+                bug = 1;
+        }
         BUG_ON(bug);
 }
 #else