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[PATCH] fix race in __block_prepare_write 

Fix a race where __block_prepare_write can leak out an in-flight read
against a bh if get_block returns an error.  This can lead to the page
becoming unlocked while the buffer is locked and the read still in flight.
__mpage_writepage BUGs on this condition.

BUG sighted on a 2-way Itanium2 system with 16K PAGE_SIZE running

	fsstress -v -d $DIR/tmp -n 1000 -p 1000 -l 2

where $DIR is a new ext2 filesystem with 4K blocks that is quite
small (causing get_block to fail often with -ENOSPC).

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Nick Piggin 2005-05-05 16:15:45 -07:00 committed by Linus Torvalds
parent 3c8fad1829
commit f3ddbdc626
1 changed files with 6 additions and 4 deletions
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10
fs/buffer.c
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@ -1953,7 +1953,7 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
if (!buffer_mapped(bh)) {
err = get_block(inode, block, bh, 1);
if (err)
goto out;
break;
if (buffer_new(bh)) {
clear_buffer_new(bh);
unmap_underlying_metadata(bh->b_bdev,
@ -1995,10 +1995,12 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
while(wait_bh > wait) {
wait_on_buffer(*--wait_bh);
if (!buffer_uptodate(*wait_bh))
return -EIO;
err = -EIO;
}
return 0;
out:
if (!err)
return err;
/* Error case: */
/*
* Zero out any newly allocated blocks to avoid exposing stale
* data. If BH_New is set, we know that the block was newly