[patch] mempool-2.5.1-D1

[Ingo Molnar <mingo@elte.hu>]

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there is another thinko in the mempool code, reported by Suparna
Bhattacharya. If mempool_alloc() is called from an IRQ context then we
return too early. The correct behavior is to allocate GFP_ATOMIC, if that
fails then we look at the pool and return an element, or return NULL.

	Ingo

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--- linux/mm/mempool.c.orig	Fri Dec 14 16:55:12 2001
+++ linux/mm/mempool.c	Fri Dec 14 17:03:52 2001
@@ -176,7 +176,8 @@
  *
  * this function only sleeps if the alloc_fn function sleeps or
  * returns NULL. Note that due to preallocation, this function
- * *never* fails.
+ * *never* fails when called from process contexts. (it might
+ * fail if called from an IRQ context.)
  */
 void * mempool_alloc(mempool_t *pool, int gfp_mask)
 {
@@ -185,7 +186,7 @@
 	struct list_head *tmp;
 	int curr_nr;
 	DECLARE_WAITQUEUE(wait, current);
-	int gfp_nowait = gfp_mask & ~__GFP_WAIT;
+	int gfp_nowait = gfp_mask & ~(__GFP_WAIT | __GFP_IO);
 
 repeat_alloc:
 	element = pool->alloc(gfp_nowait, pool->pool_data);
@@ -196,15 +197,11 @@
 	 * If the pool is less than 50% full then try harder
 	 * to allocate an element:
 	 */
-	if (gfp_mask != gfp_nowait) {
-		if (pool->curr_nr <= pool->min_nr/2) {
-			element = pool->alloc(gfp_mask, pool->pool_data);
-			if (likely(element != NULL))
-				return element;
-		}
-	} else
-		/* we must not sleep */
-		return NULL;
+	if ((gfp_mask != gfp_nowait) && (pool->curr_nr <= pool->min_nr/2)) {
+		element = pool->alloc(gfp_mask, pool->pool_data);
+		if (likely(element != NULL))
+			return element;
+	}
 
 	/*
 	 * Kick the VM at this point.
@@ -217,10 +214,12 @@
 		list_del(tmp);
 		element = tmp;
 		pool->curr_nr--;
-		spin_unlock_irqrestore(&pool->lock, flags);
-
-		return element;
+		goto out_unlock;
 	}
+	/* We must not sleep in the GFP_ATOMIC case */
+	if (gfp_mask == gfp_nowait)
+		goto out_unlock;
+
 	add_wait_queue_exclusive(&pool->wait, &wait);
 	set_task_state(current, TASK_UNINTERRUPTIBLE);
 
@@ -236,6 +235,9 @@
 	remove_wait_queue(&pool->wait, &wait);
 
 	goto repeat_alloc;
+out_unlock:
+	spin_unlock_irqrestore(&pool->lock, flags);
+	return element;
 }
 
 /**