xfs: use b_maps[] for discontiguous buffers

Commits starting at 77c1a08 introduced a multiple segment support
to xfs_buf. xfs_trans_buf_item_match() could not find a multi-segment
buffer in the transaction because it was looking at the single segment
block number rather than the multi-segment b_maps[0].bm.bn. This
results on a recursive buffer lock that can never be satisfied.

This patch:
 1) Changed the remaining b_map accesses to be b_maps[0] accesses.
 2) Renames the single segment b_map structure to __b_map to avoid
    future confusion.

Signed-off-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

2 files changed, 9 insertions, 9 deletions

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 26673a0b20e7..56d1614760cf 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -175,7 +175,7 @@ xfs_buf_get_maps(
         bp->b_map_count = map_count;
 
         if (map_count == 1) {
-                bp->b_maps = &bp->b_map;
+                bp->b_maps = &bp->__b_map;
                 return 0;
         }
 
@@ -193,7 +193,7 @@ static void
 xfs_buf_free_maps(
         struct xfs_buf  *bp)
 {
-        if (bp->b_maps != &bp->b_map) {
+        if (bp->b_maps != &bp->__b_map) {
                 kmem_free(bp->b_maps);
                 bp->b_maps = NULL;
         }
@@ -377,8 +377,8 @@ xfs_buf_allocate_memory(
         }
 
 use_alloc_page:
-        start = BBTOB(bp->b_map.bm_bn) >> PAGE_SHIFT;
-        end = (BBTOB(bp->b_map.bm_bn + bp->b_length) + PAGE_SIZE - 1)
+        start = BBTOB(bp->b_maps[0].bm_bn) >> PAGE_SHIFT;
+        end = (BBTOB(bp->b_maps[0].bm_bn + bp->b_length) + PAGE_SIZE - 1)
                                                                 >> PAGE_SHIFT;
         page_count = end - start;
         error = _xfs_buf_get_pages(bp, page_count, flags);
@@ -640,7 +640,7 @@ _xfs_buf_read(
         xfs_buf_flags_t         flags)
 {
         ASSERT(!(flags & XBF_WRITE));
-        ASSERT(bp->b_map.bm_bn != XFS_BUF_DADDR_NULL);
+        ASSERT(bp->b_maps[0].bm_bn != XFS_BUF_DADDR_NULL);
 
         bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD);
         bp->b_flags |= flags & (XBF_READ | XBF_ASYNC | XBF_READ_AHEAD);
@@ -1709,7 +1709,7 @@ xfs_buf_cmp(
         struct xfs_buf  *bp = container_of(b, struct xfs_buf, b_list);
         xfs_daddr_t             diff;
 
-        diff = ap->b_map.bm_bn - bp->b_map.bm_bn;
+        diff = ap->b_maps[0].bm_bn - bp->b_maps[0].bm_bn;
         if (diff < 0)
                 return -1;
         if (diff > 0)
diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h
index 23f5642480bb..433a12ed7b17 100644
--- a/fs/xfs/xfs_buf.h
+++ b/fs/xfs/xfs_buf.h
@@ -151,7 +151,7 @@ typedef struct xfs_buf {
         struct page             **b_pages;      /* array of page pointers */
         struct page             *b_page_array[XB_PAGES]; /* inline pages */
         struct xfs_buf_map      *b_maps;        /* compound buffer map */
-        struct xfs_buf_map      b_map;          /* inline compound buffer map */
+        struct xfs_buf_map      __b_map;        /* inline compound buffer map */
         int                     b_map_count;
         int                     b_io_length;    /* IO size in BBs */
         atomic_t                b_pin_count;    /* pin count */
@@ -330,8 +330,8 @@ void xfs_buf_stale(struct xfs_buf *bp);
  * In future, uncached buffers will pass the block number directly to the io
  * request function and hence these macros will go away at that point.
  */
-#define XFS_BUF_ADDR(bp)                ((bp)->b_map.bm_bn)
-#define XFS_BUF_SET_ADDR(bp, bno)       ((bp)->b_map.bm_bn = (xfs_daddr_t)(bno))
+#define XFS_BUF_ADDR(bp)                ((bp)->b_maps[0].bm_bn)
+#define XFS_BUF_SET_ADDR(bp, bno)       ((bp)->b_maps[0].bm_bn = (xfs_daddr_t)(bno))
 
 static inline void xfs_buf_set_ref(struct xfs_buf *bp, int lru_ref)
 {