pnfs/blocklayout: correctly decrement extent length

When we do non-page sized reads we can underflow the extent_length variable
and read incorrect data.  Fix the extent_length calculation and change to
defensive <= checks for the extent length in the read and write path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
index 5427ae766f06bbe1dc141e1eca168f593984a88b..87a633d035078dec07441cede0a60d3a6ae37283 100644 (file)
--- a/fs/nfs/blocklayout/blocklayout.c
+++ b/fs/nfs/blocklayout/blocklayout.c
@@ -272,7 +272,7 @@ bl_read_pagelist(struct nfs_pgio_header *hdr)
        isect = (sector_t) (f_offset >> SECTOR_SHIFT);
        /* Code assumes extents are page-aligned */
        for (i = pg_index; i < hdr->page_array.npages; i++) {
-               if (!extent_length) {
+               if (extent_length <= 0) {
                        /* We've used up the previous extent */
                        bl_put_extent(be);
                        bl_put_extent(cow_read);
@@ -303,6 +303,7 @@ bl_read_pagelist(struct nfs_pgio_header *hdr)
                        f_offset += pg_len;
                        bytes_left -= pg_len;
                        isect += (pg_offset >> SECTOR_SHIFT);
+                       extent_length -= (pg_offset >> SECTOR_SHIFT);
                } else {
                        pg_offset = 0;
                        pg_len = PAGE_CACHE_SIZE;
@@ -333,7 +334,7 @@ bl_read_pagelist(struct nfs_pgio_header *hdr)
                        }
                }
                isect += (pg_len >> SECTOR_SHIFT);
-               extent_length -= PAGE_CACHE_SECTORS;
+               extent_length -= (pg_len >> SECTOR_SHIFT);
        }
        if ((isect << SECTOR_SHIFT) >= header->inode->i_size) {
                hdr->res.eof = 1;
@@ -797,7 +798,7 @@ next_page:
        /* Middle pages */
        pg_index = header->args.pgbase >> PAGE_CACHE_SHIFT;
        for (i = pg_index; i < header->page_array.npages; i++) {
-               if (!extent_length) {
+               if (extent_length <= 0) {
                        /* We've used up the previous extent */
                        bl_put_extent(be);
                        bl_put_extent(cow_read);