Fix bug in block_truncate_page().
When buffers are attached to an uptodate page, they are marked as
being uptodate. To preserve buffer/page state coherency. Dirtiness
is handled in the same way.
But block_truncate_page() assumes that a buffer which is unmapped and
uptodate is over a hole. That's not the case, and the net effect is
that block_truncate_page() is failing to zero the block outside the
truncation point.
This only happens if the page has a disk mapping but has no attached
buffers on entry to block_truncate_page(). That's never the case in
current kernels, so the problem does not exhibit (it _does_ exhibit
with direct-to-BIO bypass-the-buffers I/O).
There are actually three possible states of buffer mappedness:
- Buffer has a disk mapping (buffer_mapped(bh) == true)
- buffer is over a hole (buffer_mapped(bh) == false)
- don't know. Need to run get_block() (buffer_mapped(bh) == false)
This ambiguity could be resolved by added another buffer state bit
(BH_mapping_state_known?) but given that we already elide the get_block
calls for the common case (buffer outside i_size) it is unlikely that
the complexity is worthwhile.
=====================================
--- 2.5.18/fs/buffer.c~block_truncate_page Sun May 26 12:37:39 2002
+++ 2.5.18-akpm/fs/buffer.c Sun May 26 12:37:39 2002
@@ -2079,11 +2079,10 @@ int block_truncate_page(struct address_s
err = 0;
if (!buffer_mapped(bh)) {
- /* Hole? Nothing to do */
- if (buffer_uptodate(bh))
+ err = get_block(inode, iblock, bh, 0);
+ if (err)
goto unlock;
- get_block(inode, iblock, bh, 0);
- /* Still unmapped? Nothing to do */
+ /* unmapped? It's a hole - nothing to do */
if (!buffer_mapped(bh))
goto unlock;
}
--- 2.5.18/fs/ext3/inode.c~block_truncate_page Sun May 26 12:37:39 2002
+++ 2.5.18-akpm/fs/ext3/inode.c Sun May 26 12:37:40 2002
@@ -1408,11 +1408,8 @@ static int ext3_block_truncate_page(hand
err = 0;
if (!buffer_mapped(bh)) {
- /* Hole? Nothing to do */
- if (buffer_uptodate(bh))
- goto unlock;
ext3_get_block(inode, iblock, bh, 0);
- /* Still unmapped? Nothing to do */
+ /* unmapped? It's a hole - nothing to do */
if (!buffer_mapped(bh))
goto unlock;
}
-
-
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This archive was generated by hypermail 2b29 : Fri May 31 2002 - 22:00:18 EST