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[PATCH v3 1/5] xfs: use b_maps[] for discontiguous buffers

To: xfs@xxxxxxxxxxx
Subject: [PATCH v3 1/5] xfs: use b_maps[] for discontiguous buffers
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Tue, 04 Dec 2012 17:18:02 -0600
References: <20121204231801.982422341@xxxxxxx>
User-agent: quilt/0.51-1
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@xxxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/xfs/xfs_buf.c |   12 ++++++------
 fs/xfs/xfs_buf.h |    6 +++---
 2 files changed, 9 insertions(+), 9 deletions(-)

Index: b/fs/xfs/xfs_buf.c
===================================================================
--- 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)
Index: b/fs/xfs/xfs_buf.h
===================================================================
--- 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)
 {


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