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23 October 2021, 00:29:24 UTC
Revision 914ee295af418e936ec20a08c1663eaabe4cd07a authored by Xin Zhong on 09 December 2010, 09:30:14 UTC, committed by Chris Mason on 10 December 2010, 21:29:10 UTC 
Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
 
This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical region in
btrfs_copy_from_user().

Reviewed-by: Yan, Zheng<zheng.z.yan@intel.com>
Signed-off-by: Zhong, Xin <xin.zhong@intel.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
1 parent f106e82
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Tip revision: 914ee295af418e936ec20a08c1663eaabe4cd07a authored by Xin Zhong on 09 December 2010, 09:30:14 UTC
Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
Tip revision: 914ee29
io.c 
/*
 * linux/fs/befs/io.c
 *
 * Copyright (C) 2001 Will Dyson <will_dyson@pobox.com
 *
 * Based on portions of file.c and inode.c 
 * by Makoto Kato (m_kato@ga2.so-net.ne.jp)
 *
 * Many thanks to Dominic Giampaolo, author of Practical File System
 * Design with the Be File System, for such a helpful book.
 *
 */

#include <linux/buffer_head.h>

#include "befs.h"
#include "io.h"

/*
 * Converts befs notion of disk addr to a disk offset and uses
 * linux kernel function sb_bread() to get the buffer containing
 * the offset. -Will Dyson
 *
 */

struct buffer_head *
befs_bread_iaddr(struct super_block *sb, befs_inode_addr iaddr)
{
	struct buffer_head *bh = NULL;
	befs_blocknr_t block = 0;
	befs_sb_info *befs_sb = BEFS_SB(sb);

	befs_debug(sb, "---> Enter befs_read_iaddr() "
		   "[%u, %hu, %hu]",
		   iaddr.allocation_group, iaddr.start, iaddr.len);

	if (iaddr.allocation_group > befs_sb->num_ags) {
		befs_error(sb, "BEFS: Invalid allocation group %u, max is %u",
			   iaddr.allocation_group, befs_sb->num_ags);
		goto error;
	}

	block = iaddr2blockno(sb, &iaddr);

	befs_debug(sb, "befs_read_iaddr: offset = %lu", block);

	bh = sb_bread(sb, block);

	if (bh == NULL) {
		befs_error(sb, "Failed to read block %lu", block);
		goto error;
	}

	befs_debug(sb, "<--- befs_read_iaddr()");
	return bh;

      error:
	befs_debug(sb, "<--- befs_read_iaddr() ERROR");
	return NULL;
}

struct buffer_head *
befs_bread(struct super_block *sb, befs_blocknr_t block)
{
	struct buffer_head *bh = NULL;

	befs_debug(sb, "---> Enter befs_read() %Lu", block);

	bh = sb_bread(sb, block);

	if (bh == NULL) {
		befs_error(sb, "Failed to read block %lu", block);
		goto error;
	}

	befs_debug(sb, "<--- befs_read()");

	return bh;

      error:
	befs_debug(sb, "<--- befs_read() ERROR");
	return NULL;
}
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