1 files changed, 14 insertions, 7 deletions

diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
index cc9b450399df..a178f5ebea78 100644
--- a/fs/btrfs/lzo.c
+++ b/fs/btrfs/lzo.c
@@ -280,6 +280,7 @@ static int lzo_decompress_biovec(struct list_head *ws,
         unsigned long tot_out;
         unsigned long tot_len;
         char *buf;
+        bool may_late_unmap, need_unmap;
 
         data_in = kmap(pages_in[0]);
         tot_len = read_compress_length(data_in);
@@ -300,11 +301,13 @@ static int lzo_decompress_biovec(struct list_head *ws,
 
                 tot_in += in_len;
                 working_bytes = in_len;
+                may_late_unmap = need_unmap = false;
 
                 /* fast path: avoid using the working buffer */
                 if (in_page_bytes_left >= in_len) {
                         buf = data_in + in_offset;
                         bytes = in_len;
+                        may_late_unmap = true;
                         goto cont;
                 }
 
@@ -329,14 +332,17 @@ cont:
                                 if (working_bytes == 0 && tot_in >= tot_len)
                                         break;
 
-                                kunmap(pages_in[page_in_index]);
-                                page_in_index++;
-                                if (page_in_index >= total_pages_in) {
+                                if (page_in_index + 1 >= total_pages_in) {
                                         ret = -1;
-                                        data_in = NULL;
                                         goto done;
                                 }
-                                data_in = kmap(pages_in[page_in_index]);
+
+                                if (may_late_unmap)
+                                        need_unmap = true;
+                                else
+                                        kunmap(pages_in[page_in_index]);
+
+                                data_in = kmap(pages_in[++page_in_index]);
 
                                 in_page_bytes_left = PAGE_CACHE_SIZE;
                                 in_offset = 0;
@@ -346,6 +352,8 @@ cont:
                 out_len = lzo1x_worst_compress(PAGE_CACHE_SIZE);
                 ret = lzo1x_decompress_safe(buf, in_len, workspace->buf,
                                             &out_len);
+                if (need_unmap)
+                        kunmap(pages_in[page_in_index - 1]);
                 if (ret != LZO_E_OK) {
                         printk(KERN_WARNING "btrfs decompress failed\n");
                         ret = -1;
@@ -363,8 +371,7 @@ cont:
                         break;
         }
 done:
-        if (data_in)
-                kunmap(pages_in[page_in_index]);
+        kunmap(pages_in[page_in_index]);
         return ret;
 }