[PATCH] adapt page_lock_anon_vma() to PREEMPT_RCU

[Oleg Nesterov]

page_lock_anon_vma() uses spin_lock() to block RCU. This doesn't work with
PREEMPT_RCU, we have to do rcu_read_lock() explicitely. Otherwise, it is
theoretically possible that slab returns anon_vma's memory to the system
before we do spin_unlock(&anon_vma->lock).

Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>

--- WQ/mm/rmap.c~       2007-02-18 22:56:49.000000000 +0300
+++ WQ/mm/rmap.c        2007-02-25 22:43:00.000000000 +0300
@@ -183,7 +183,7 @@ void __init anon_vma_init(void)
  */
 static struct anon_vma *page_lock_anon_vma(struct page *page)
 {
-       struct anon_vma *anon_vma = NULL;
+       struct anon_vma *anon_vma;
        unsigned long anon_mapping;
 
        rcu_read_lock();
@@ -195,9 +195,16 @@ static struct anon_vma *page_lock_anon_v
 
        anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
        spin_lock(&anon_vma->lock);
+       return anon_vma;
 out:
        rcu_read_unlock();
-       return anon_vma;
+       return NULL;
+}
+
+static void page_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+       spin_unlock(&anon_vma->lock);
+       rcu_read_unlock();
 }
 
 /*
@@ -333,7 +340,8 @@ static int page_referenced_anon(struct p
                if (!mapcount)
                        break;
        }
-       spin_unlock(&anon_vma->lock);
+
+       page_unlock_anon_vma(anon_vma);
        return referenced;
 }
 
@@ -809,7 +817,8 @@ static int try_to_unmap_anon(struct page
                                !page_mapped(page))
                        break;
        }
-       spin_unlock(&anon_vma->lock);
+
+       page_unlock_anon_vma(anon_vma);
        return ret;
 }
 

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