From 8d183980d962104d078680ed75ee8be299d782dc Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton@redhat.com>
Date: Wed, 11 Jul 2012 09:09:36 -0400
Subject: [PATCH] --- yaml --- r: 312053 b: refs/heads/master c:
 3cf003c08be785af4bee9ac05891a15bcbff856a h: refs/heads/master i:   312051:
 6fe7b67ab99e4b396d4b0797e7cb59ec4daed6de v: v3

---
 [refs]                  |  2 +-
 trunk/fs/cifs/cifssmb.c | 30 +++++++++++++++++++++++++++++-
 2 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/[refs] b/[refs]
index 1a3c0687bcee..e2117bbc8e8a 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 3ae629d98bd5ed77585a878566f04f310adbc591
+refs/heads/master: 3cf003c08be785af4bee9ac05891a15bcbff856a
diff --git a/trunk/fs/cifs/cifssmb.c b/trunk/fs/cifs/cifssmb.c
index 5b400730c213..4ee522b3f66f 100644
--- a/trunk/fs/cifs/cifssmb.c
+++ b/trunk/fs/cifs/cifssmb.c
@@ -86,7 +86,31 @@ static struct {
 #endif /* CONFIG_CIFS_WEAK_PW_HASH */
 #endif /* CIFS_POSIX */
 
-/* Forward declarations */
+#ifdef CONFIG_HIGHMEM
+/*
+ * On arches that have high memory, kmap address space is limited. By
+ * serializing the kmap operations on those arches, we ensure that we don't
+ * end up with a bunch of threads in writeback with partially mapped page
+ * arrays, stuck waiting for kmap to come back. That situation prevents
+ * progress and can deadlock.
+ */
+static DEFINE_MUTEX(cifs_kmap_mutex);
+
+static inline void
+cifs_kmap_lock(void)
+{
+	mutex_lock(&cifs_kmap_mutex);
+}
+
+static inline void
+cifs_kmap_unlock(void)
+{
+	mutex_unlock(&cifs_kmap_mutex);
+}
+#else /* !CONFIG_HIGHMEM */
+#define cifs_kmap_lock() do { ; } while(0)
+#define cifs_kmap_unlock() do { ; } while(0)
+#endif /* CONFIG_HIGHMEM */
 
 /* Mark as invalid, all open files on tree connections since they
    were closed when session to server was lost */
@@ -1503,7 +1527,9 @@ cifs_readv_receive(struct TCP_Server_Info *server, struct mid_q_entry *mid)
 	}
 
 	/* marshal up the page array */
+	cifs_kmap_lock();
 	len = rdata->marshal_iov(rdata, data_len);
+	cifs_kmap_unlock();
 	data_len -= len;
 
 	/* issue the read if we have any iovecs left to fill */
@@ -2069,7 +2095,9 @@ cifs_async_writev(struct cifs_writedata *wdata)
 	 * and set the iov_len properly for each one. It may also set
 	 * wdata->bytes too.
 	 */
+	cifs_kmap_lock();
 	wdata->marshal_iov(iov, wdata);
+	cifs_kmap_unlock();
 
 	cFYI(1, "async write at %llu %u bytes", wdata->offset, wdata->bytes);