Reenabled linux-xen and xen-image build

[people/pmueller/ipfire-2.x.git] / src / patches / suse-2.6.27.25 / patches.fixes / mm-nr_pdflush-race-fix.patch

Subject: mm: fix pdflush thread creation upper bound.
From: Peter W. Morreale <pmorreale@novell.com>
References: bnc#460284
Patch-upstream: not yet
    
    This patch fixes a race on creating pdflush threads.  Without the patch,
    it is possible to create more than MAX_PDFLUSH_THREADS threads, and this
    has been observed in practice.
    
    The fix involves moving the lock around to protect the check against the
    thread count and correctly dealing with thread creation failure.
    
    Signed-Off-By:   Peter W. Morreale <pmorreale@novell.com>
Acked-by: Nick Piggin <npiggin@suse.de>
---
---
 mm/pdflush.c |   27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

--- a/mm/pdflush.c
+++ b/mm/pdflush.c
@@ -98,7 +98,6 @@ static int __pdflush(struct pdflush_work
 	INIT_LIST_HEAD(&my_work->list);
 
 	spin_lock_irq(&pdflush_lock);
-	nr_pdflush_threads++;
 	for ( ; ; ) {
 		struct pdflush_work *pdf;
 
@@ -126,20 +125,23 @@ static int __pdflush(struct pdflush_work
 
 		(*my_work->fn)(my_work->arg0);
 
+		spin_lock_irq(&pdflush_lock);
+
 		/*
 		 * Thread creation: For how long have there been zero
 		 * available threads?
 		 */
 		if (time_after(jiffies, last_empty_jifs + 1 * HZ)) {
-			/* unlocked list_empty() test is OK here */
 			if (list_empty(&pdflush_list)) {
-				/* unlocked test is OK here */
-				if (nr_pdflush_threads < MAX_PDFLUSH_THREADS)
+				if (nr_pdflush_threads < MAX_PDFLUSH_THREADS) {
+					nr_pdflush_threads++;
+					spin_unlock_irq(&pdflush_lock);
 					start_one_pdflush_thread();
+					spin_lock_irq(&pdflush_lock);
+				}
 			}
 		}
 
-		spin_lock_irq(&pdflush_lock);
 		my_work->fn = NULL;
 
 		/*
@@ -226,13 +228,26 @@ int pdflush_operation(void (*fn)(unsigne
 
 static void start_one_pdflush_thread(void)
 {
-	kthread_run(pdflush, NULL, "pdflush");
+	struct task_struct *k;
+
+	k = kthread_run(pdflush, NULL, "pdflush");
+	if (unlikely(IS_ERR(k))) {
+		spin_lock_irq(&pdflush_lock);
+		nr_pdflush_threads--;
+		spin_unlock_irq(&pdflush_lock);
+	}
 }
 
 static int __init pdflush_init(void)
 {
 	int i;
 
+	/*
+	 * Pre-set nr_pdflush_threads...  If we fail to create,
+	 * the count will be decremented.
+	 */
+	nr_pdflush_threads = MIN_PDFLUSH_THREADS;
+
 	for (i = 0; i < MIN_PDFLUSH_THREADS; i++)
 		start_one_pdflush_thread();
 	return 0;