From: Omar Sandoval <osan...@fb.com>

In convert_free_space_to_{bitmaps,extents}(), we buffer the free space
bitmaps in memory and copy them directly to/from the extent buffers with
{read,write}_extent_buffer(). The extent buffer bitmap helpers use byte
granularity, which is equivalent to a little-endian bitmap. This means
that on big-endian systems, the in-memory bitmaps will be written to
disk byte-swapped. To fix this, use byte-granularity for the bitmaps in
memory.

Fixes: a5ed91828518 ("Btrfs: implement the free space B-tree")
Cc: sta...@vger.kernel.org # 4.5+
Signed-off-by: Omar Sandoval <osan...@fb.com>
---
 fs/btrfs/extent_io.c       | 64 +++++++++++++++++++++++++++++++++-------------
 fs/btrfs/extent_io.h       | 22 ++++++++++++++++
 fs/btrfs/free-space-tree.c | 17 ++++++------
 3 files changed, 76 insertions(+), 27 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 44fe66b..c3ec30d 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5524,17 +5524,45 @@ void copy_extent_buffer(struct extent_buffer *dst, 
struct extent_buffer *src,
        }
 }
 
-/*
- * The extent buffer bitmap operations are done with byte granularity because
- * bitmap items are not guaranteed to be aligned to a word and therefore a
- * single word in a bitmap may straddle two pages in the extent buffer.
- */
-#define BIT_BYTE(nr) ((nr) / BITS_PER_BYTE)
-#define BYTE_MASK ((1 << BITS_PER_BYTE) - 1)
-#define BITMAP_FIRST_BYTE_MASK(start) \
-       ((BYTE_MASK << ((start) & (BITS_PER_BYTE - 1))) & BYTE_MASK)
-#define BITMAP_LAST_BYTE_MASK(nbits) \
-       (BYTE_MASK >> (-(nbits) & (BITS_PER_BYTE - 1)))
+void le_bitmap_set(u8 *map, unsigned int start, int len)
+{
+       u8 *p = map + BIT_BYTE(start);
+       const unsigned int size = start + len;
+       int bits_to_set = BITS_PER_BYTE - (start % BITS_PER_BYTE);
+       u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(start);
+
+       while (len - bits_to_set >= 0) {
+               *p |= mask_to_set;
+               len -= bits_to_set;
+               bits_to_set = BITS_PER_BYTE;
+               mask_to_set = ~(u8)0;
+               p++;
+       }
+       if (len) {
+               mask_to_set &= BITMAP_LAST_BYTE_MASK(size);
+               *p |= mask_to_set;
+       }
+}
+
+void le_bitmap_clear(u8 *map, unsigned int start, int len)
+{
+       u8 *p = map + BIT_BYTE(start);
+       const unsigned int size = start + len;
+       int bits_to_clear = BITS_PER_BYTE - (start % BITS_PER_BYTE);
+       u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(start);
+
+       while (len - bits_to_clear >= 0) {
+               *p &= ~mask_to_clear;
+               len -= bits_to_clear;
+               bits_to_clear = BITS_PER_BYTE;
+               mask_to_clear = ~(u8)0;
+               p++;
+       }
+       if (len) {
+               mask_to_clear &= BITMAP_LAST_BYTE_MASK(size);
+               *p &= ~mask_to_clear;
+       }
+}
 
 /*
  * eb_bitmap_offset() - calculate the page and offset of the byte containing 
the
@@ -5578,7 +5606,7 @@ static inline void eb_bitmap_offset(struct extent_buffer 
*eb,
 int extent_buffer_test_bit(struct extent_buffer *eb, unsigned long start,
                           unsigned long nr)
 {
-       char *kaddr;
+       u8 *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
@@ -5600,13 +5628,13 @@ int extent_buffer_test_bit(struct extent_buffer *eb, 
unsigned long start,
 void extent_buffer_bitmap_set(struct extent_buffer *eb, unsigned long start,
                              unsigned long pos, unsigned long len)
 {
-       char *kaddr;
+       u8 *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
        const unsigned int size = pos + len;
        int bits_to_set = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
-       unsigned int mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);
+       u8 mask_to_set = BITMAP_FIRST_BYTE_MASK(pos);
 
        eb_bitmap_offset(eb, start, pos, &i, &offset);
        page = eb->pages[i];
@@ -5617,7 +5645,7 @@ void extent_buffer_bitmap_set(struct extent_buffer *eb, 
unsigned long start,
                kaddr[offset] |= mask_to_set;
                len -= bits_to_set;
                bits_to_set = BITS_PER_BYTE;
-               mask_to_set = ~0U;
+               mask_to_set = ~(u8)0;
                if (++offset >= PAGE_SIZE && len > 0) {
                        offset = 0;
                        page = eb->pages[++i];
@@ -5642,13 +5670,13 @@ void extent_buffer_bitmap_set(struct extent_buffer *eb, 
unsigned long start,
 void extent_buffer_bitmap_clear(struct extent_buffer *eb, unsigned long start,
                                unsigned long pos, unsigned long len)
 {
-       char *kaddr;
+       u8 *kaddr;
        struct page *page;
        unsigned long i;
        size_t offset;
        const unsigned int size = pos + len;
        int bits_to_clear = BITS_PER_BYTE - (pos % BITS_PER_BYTE);
-       unsigned int mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);
+       u8 mask_to_clear = BITMAP_FIRST_BYTE_MASK(pos);
 
        eb_bitmap_offset(eb, start, pos, &i, &offset);
        page = eb->pages[i];
@@ -5659,7 +5687,7 @@ void extent_buffer_bitmap_clear(struct extent_buffer *eb, 
unsigned long start,
                kaddr[offset] &= ~mask_to_clear;
                len -= bits_to_clear;
                bits_to_clear = BITS_PER_BYTE;
-               mask_to_clear = ~0U;
+               mask_to_clear = ~(u8)0;
                if (++offset >= PAGE_SIZE && len > 0) {
                        offset = 0;
                        page = eb->pages[++i];
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 28cd88f..1cf4e42 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -59,6 +59,28 @@
  */
 #define EXTENT_PAGE_PRIVATE 1
 
+/*
+ * The extent buffer bitmap operations are done with byte granularity instead 
of
+ * word granularity for two reasons:
+ * 1. The bitmaps must be little-endian on disk.
+ * 2. Bitmap items are not guaranteed to be aligned to a word and therefore a
+ *    single word in a bitmap may straddle two pages in the extent buffer.
+ */
+#define BIT_BYTE(nr) ((nr) / BITS_PER_BYTE)
+#define BYTE_MASK ((1 << BITS_PER_BYTE) - 1)
+#define BITMAP_FIRST_BYTE_MASK(start) \
+       ((BYTE_MASK << ((start) & (BITS_PER_BYTE - 1))) & BYTE_MASK)
+#define BITMAP_LAST_BYTE_MASK(nbits) \
+       (BYTE_MASK >> (-(nbits) & (BITS_PER_BYTE - 1)))
+
+static inline int le_test_bit(int nr, const u8 *addr)
+{
+       return 1U & (addr[BIT_BYTE(nr)] >> (nr & (BITS_PER_BYTE-1)));
+}
+
+extern void le_bitmap_set(u8 *map, unsigned int start, int len);
+extern void le_bitmap_clear(u8 *map, unsigned int start, int len);
+
 struct extent_state;
 struct btrfs_root;
 struct btrfs_io_bio;
diff --git a/fs/btrfs/free-space-tree.c b/fs/btrfs/free-space-tree.c
index 87e7e3d..8fd85bf 100644
--- a/fs/btrfs/free-space-tree.c
+++ b/fs/btrfs/free-space-tree.c
@@ -151,7 +151,7 @@ static inline u32 free_space_bitmap_size(u64 size, u32 
sectorsize)
        return DIV_ROUND_UP((u32)div_u64(size, sectorsize), BITS_PER_BYTE);
 }
 
-static unsigned long *alloc_bitmap(u32 bitmap_size)
+static u8 *alloc_bitmap(u32 bitmap_size)
 {
        void *mem;
 
@@ -180,8 +180,7 @@ int convert_free_space_to_bitmaps(struct btrfs_trans_handle 
*trans,
        struct btrfs_free_space_info *info;
        struct btrfs_key key, found_key;
        struct extent_buffer *leaf;
-       unsigned long *bitmap;
-       char *bitmap_cursor;
+       u8 *bitmap, *bitmap_cursor;
        u64 start, end;
        u64 bitmap_range, i;
        u32 bitmap_size, flags, expected_extent_count;
@@ -231,7 +230,7 @@ int convert_free_space_to_bitmaps(struct btrfs_trans_handle 
*trans,
                                                block_group->sectorsize);
                                last = div_u64(found_key.objectid + 
found_key.offset - start,
                                               block_group->sectorsize);
-                               bitmap_set(bitmap, first, last - first);
+                               le_bitmap_set(bitmap, first, last - first);
 
                                extent_count++;
                                nr++;
@@ -269,7 +268,7 @@ int convert_free_space_to_bitmaps(struct btrfs_trans_handle 
*trans,
                goto out;
        }
 
-       bitmap_cursor = (char *)bitmap;
+       bitmap_cursor = bitmap;
        bitmap_range = block_group->sectorsize * BTRFS_FREE_SPACE_BITMAP_BITS;
        i = start;
        while (i < end) {
@@ -318,7 +317,7 @@ int convert_free_space_to_extents(struct btrfs_trans_handle 
*trans,
        struct btrfs_free_space_info *info;
        struct btrfs_key key, found_key;
        struct extent_buffer *leaf;
-       unsigned long *bitmap;
+       u8 *bitmap;
        u64 start, end;
        /* Initialize to silence GCC. */
        u64 extent_start = 0;
@@ -362,7 +361,7 @@ int convert_free_space_to_extents(struct btrfs_trans_handle 
*trans,
                                break;
                        } else if (found_key.type == 
BTRFS_FREE_SPACE_BITMAP_KEY) {
                                unsigned long ptr;
-                               char *bitmap_cursor;
+                               u8 *bitmap_cursor;
                                u32 bitmap_pos, data_size;
 
                                ASSERT(found_key.objectid >= start);
@@ -372,7 +371,7 @@ int convert_free_space_to_extents(struct btrfs_trans_handle 
*trans,
                                bitmap_pos = div_u64(found_key.objectid - start,
                                                     block_group->sectorsize *
                                                     BITS_PER_BYTE);
-                               bitmap_cursor = ((char *)bitmap) + bitmap_pos;
+                               bitmap_cursor = bitmap + bitmap_pos;
                                data_size = 
free_space_bitmap_size(found_key.offset,
                                                                   
block_group->sectorsize);
 
@@ -409,7 +408,7 @@ int convert_free_space_to_extents(struct btrfs_trans_handle 
*trans,
        offset = start;
        bitnr = 0;
        while (offset < end) {
-               bit = !!test_bit(bitnr, bitmap);
+               bit = !!le_test_bit(bitnr, bitmap);
                if (prev_bit == 0 && bit == 1) {
                        extent_start = offset;
                } else if (prev_bit == 1 && bit == 0) {
-- 
2.10.0

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