From: Robin Holt <holt@sgi.com>
Date: Wed, 16 Dec 2009 00:47:57 +0000 (-0800)
Subject: x86: uv: xpc NULL deref when mesq becomes empty
X-Git-Tag: v2.6.33-rc1~71^2~44
X-Git-Url: http://ftp.safe.ca/?p=safe%2Fjmp%2Flinux-2.6;a=commitdiff_plain;h=15b87d67ff3dc042bee42f991858d6b121b3b3ca

x86: uv: xpc NULL deref when mesq becomes empty

Under heavy load conditions, our set of xpc messages may become exhausted.
 The code handles this correctly with the exception of the management code
which hits a NULL pointer dereference.

Signed-off-by: Robin Holt <holt@sgi.com>
Cc: Jack Steiner <steiner@sgi.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

diff --git a/drivers/misc/sgi-xp/xpc_uv.c b/drivers/misc/sgi-xp/xpc_uv.c
index bbf0e2e..19bd7b0 100644
--- a/drivers/misc/sgi-xp/xpc_uv.c
+++ b/drivers/misc/sgi-xp/xpc_uv.c
@@ -949,11 +949,13 @@ xpc_get_fifo_entry_uv(struct xpc_fifo_head_uv *head)
 		head->first = first->next;
 		if (head->first == NULL)
 			head->last = NULL;
+
+		head->n_entries--;
+		BUG_ON(head->n_entries < 0);
+
+		first->next = NULL;
 	}
-	head->n_entries--;
-	BUG_ON(head->n_entries < 0);
 	spin_unlock_irqrestore(&head->lock, irq_flags);
-	first->next = NULL;
 	return first;
 }