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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
super.c 
/*
 * super.c
 *
 * Copyright (C) 2001-2002 Will Dyson <will_dyson@pobox.com>
 *
 * Licensed under the GNU GPL. See the file COPYING for details.
 *
 */

#include <linux/fs.h>
#include <asm/page.h> /* for PAGE_SIZE */

#include "befs.h"
#include "super.h"

/**
 * load_befs_sb -- Read from disk and properly byteswap all the fields
 * of the befs superblock
 *
 *
 *
 *
 */
int
befs_load_sb(struct super_block *sb, befs_super_block * disk_sb)
{
	befs_sb_info *befs_sb = BEFS_SB(sb);

	/* Check the byte order of the filesystem */
	if (disk_sb->fs_byte_order == BEFS_BYTEORDER_NATIVE_LE)
	    befs_sb->byte_order = BEFS_BYTESEX_LE;
	else if (disk_sb->fs_byte_order == BEFS_BYTEORDER_NATIVE_BE)
	    befs_sb->byte_order = BEFS_BYTESEX_BE;

	befs_sb->magic1 = fs32_to_cpu(sb, disk_sb->magic1);
	befs_sb->magic2 = fs32_to_cpu(sb, disk_sb->magic2);
	befs_sb->magic3 = fs32_to_cpu(sb, disk_sb->magic3);
	befs_sb->block_size = fs32_to_cpu(sb, disk_sb->block_size);
	befs_sb->block_shift = fs32_to_cpu(sb, disk_sb->block_shift);
	befs_sb->num_blocks = fs64_to_cpu(sb, disk_sb->num_blocks);
	befs_sb->used_blocks = fs64_to_cpu(sb, disk_sb->used_blocks);
	befs_sb->inode_size = fs32_to_cpu(sb, disk_sb->inode_size);

	befs_sb->blocks_per_ag = fs32_to_cpu(sb, disk_sb->blocks_per_ag);
	befs_sb->ag_shift = fs32_to_cpu(sb, disk_sb->ag_shift);
	befs_sb->num_ags = fs32_to_cpu(sb, disk_sb->num_ags);

	befs_sb->log_blocks = fsrun_to_cpu(sb, disk_sb->log_blocks);
	befs_sb->log_start = fs64_to_cpu(sb, disk_sb->log_start);
	befs_sb->log_end = fs64_to_cpu(sb, disk_sb->log_end);

	befs_sb->root_dir = fsrun_to_cpu(sb, disk_sb->root_dir);
	befs_sb->indices = fsrun_to_cpu(sb, disk_sb->indices);
	befs_sb->nls = NULL;

	return BEFS_OK;
}

int
befs_check_sb(struct super_block *sb)
{
	befs_sb_info *befs_sb = BEFS_SB(sb);

	/* Check magic headers of super block */
	if ((befs_sb->magic1 != BEFS_SUPER_MAGIC1)
	    || (befs_sb->magic2 != BEFS_SUPER_MAGIC2)
	    || (befs_sb->magic3 != BEFS_SUPER_MAGIC3)) {
		befs_error(sb, "invalid magic header");
		return BEFS_ERR;
	}

	/*
	 * Check blocksize of BEFS.
	 *
	 * Blocksize of BEFS is 1024, 2048, 4096 or 8192.
	 */

	if ((befs_sb->block_size != 1024)
	    && (befs_sb->block_size != 2048)
	    && (befs_sb->block_size != 4096)
	    && (befs_sb->block_size != 8192)) {
		befs_error(sb, "invalid blocksize: %u", befs_sb->block_size);
		return BEFS_ERR;
	}

	if (befs_sb->block_size > PAGE_SIZE) {
		befs_error(sb, "blocksize(%u) cannot be larger"
			   "than system pagesize(%lu)", befs_sb->block_size,
			   PAGE_SIZE);
		return BEFS_ERR;
	}

	/*
	   * block_shift and block_size encode the same information
	   * in different ways as a consistency check.
	 */

	if ((1 << befs_sb->block_shift) != befs_sb->block_size) {
		befs_error(sb, "block_shift disagrees with block_size. "
			   "Corruption likely.");
		return BEFS_ERR;
	}

	if (befs_sb->log_start != befs_sb->log_end) {
		befs_error(sb, "Filesystem not clean! There are blocks in the "
			   "journal. You must boot into BeOS and mount this volume "
			   "to make it clean.");
		return BEFS_ERR;
	}

	return BEFS_OK;
}
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