Commit f3ddbdc6 authored May 05, 2005 by Nick Piggin Committed by Linus Torvalds May 05, 2005

[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>

parent 3c8fad18

fs/buffer.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -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

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