---

yaml
---
r: 312053
b: refs/heads/master
c: 3cf003c
h: refs/heads/master
i:
  312051: 6fe7b67
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 3ae629d98bd5ed77585a878566f04f310adbc591
+refs/heads/master: 3cf003c08be785af4bee9ac05891a15bcbff856a

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);