fs/autofs4/waitq.c |   21 +++++++++++++++++++--
 1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index da8876d38a7b..f6fcca58e0e3 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -15,6 +15,7 @@
 #include <linux/time.h>
 #include <linux/signal.h>
 #include <linux/file.h>
+#include <linux/compat.h>
 #include "autofs_i.h"
 
 /* We make this a static variable rather than a part of the superblock; it
@@ -91,6 +92,23 @@ static int autofs4_write(struct autofs_sb_info *sbi,
 
 	return (bytes > 0);
 }
+
+/*
+ * The autofs_v5 packet was misdesigned.
+ *
+ * The packets are identical on x86-32 and x86-64, but have different
+ * alignment. Which means that 'sizeof()' will give different results.
+ * Fix it up for the case of running 32-bit user mode on a 64-bit kernel.
+ */
+static noinline size_t autofs_v5_packet_size(void)
+{
+	size_t pktsz = sizeof(struct autofs_v5_packet);
+#if defined(CONFIG_X86_64) && defined(CONFIG_COMPAT)
+	if (is_compat_task())
+		pktsz -= 4;
+#endif
+	return pktsz;
+}
 	
 static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
 				 struct autofs_wait_queue *wq,
@@ -155,8 +173,7 @@ static void autofs4_notify_daemon(struct autofs_sb_info *sbi,
 	{
 		struct autofs_v5_packet *packet = &pkt.v5_pkt.v5_packet;
 
-		pktsz = sizeof(*packet);
-
+		pktsz = autofs_v5_packet_size();
 		packet->wait_queue_token = wq->wait_queue_token;
 		packet->len = wq->name.len;
 		memcpy(packet->name, wq->name.name, wq->name.len);