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ext4: allocate entire range in zero range 

Currently there is a bug in zero range code which causes zero range
calls to only allocate block aligned portion of the range, while
ignoring the rest in some cases.

In some cases, namely if the end of the range is past i_size, we do
attempt to preallocate the last nonaligned block. However this might
cause kernel to BUG() in some carefully designed zero range requests
on setups where page size > block size.

Fix this problem by first preallocating the entire range, including
the nonaligned edges and converting the written extents to unwritten
in the next step. This approach will also give us the advantage of
having the range to be as linearly contiguous as possible.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Lukas Czerner 2015-04-03 00:09:13 -04:00 committed by Theodore Ts'o
parent 5a4f3145aa
commit 0f2af21aae
1 changed files with 19 additions and 12 deletions
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31
fs/ext4/extents.c
View File

@ -4797,12 +4797,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
else
max_blocks -= lblk;
flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT |
EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
EXT4_EX_NOCACHE;
if (mode & FALLOC_FL_KEEP_SIZE)
flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
mutex_lock(&inode->i_mutex);
/*
@ -4819,15 +4813,28 @@ static long ext4_zero_range(struct file *file, loff_t offset,
ret = inode_newsize_ok(inode, new_size);
if (ret)
goto out_mutex;
/*
* If we have a partial block after EOF we have to allocate
* the entire block.
*/
if (partial_end)
max_blocks += 1;
}
flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
if (mode & FALLOC_FL_KEEP_SIZE)
flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
/* Preallocate the range including the unaligned edges */
if (partial_begin || partial_end) {
ret = ext4_alloc_file_blocks(file,
round_down(offset, 1 << blkbits) >> blkbits,
(round_up((offset + len), 1 << blkbits) -
round_down(offset, 1 << blkbits)) >> blkbits,
new_size, flags, mode);
if (ret)
goto out_mutex;
}
/* Zero range excluding the unaligned edges */
if (max_blocks > 0) {
flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
EXT4_EX_NOCACHE);
/* Now release the pages and zero block aligned part of pages*/
truncate_pagecache_range(inode, start, end - 1);