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From: Lukas Czerner <lczerner@redhat.com>
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Date: Wed, 18 Feb 2015 17:49:28 +0100
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Subject: [PATCH] ext4: Allocate entire range in zero range
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Currently there is a bug in zero range code which causes zero range
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calls to only allocate block aligned portion of the range, while
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ignoring the rest in some cases.
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In some cases, namely if the end of the range is past isize, we do
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attempt to preallocate the last nonaligned block. However this might
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cause kernel to BUG() in some carefully designed zero range requests on
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setups where page size > block size.
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Fix this problem by first preallocating the entire range, including the
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nonaligned edges and converting the written extents to unwritten in the
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next step. This approach will also give us the advantage of having the
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range to be as linearly contiguous as possible.
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Signed-off-by: Lukas Czerner <lczerner@redhat.com>
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---
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fs/ext4/extents.c | 31 +++++++++++++++++++------------
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1 file changed, 19 insertions(+), 12 deletions(-)
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diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
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index 0b16fb4c06d3..e3bf236a36ac 100644
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--- a/fs/ext4/extents.c
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+++ b/fs/ext4/extents.c
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@@ -4792,12 +4792,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
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else
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max_blocks -= lblk;
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- flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT |
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- EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
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- EXT4_EX_NOCACHE;
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- if (mode & FALLOC_FL_KEEP_SIZE)
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- flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
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-
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mutex_lock(&inode->i_mutex);
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/*
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@@ -4814,15 +4808,28 @@ static long ext4_zero_range(struct file *file, loff_t offset,
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ret = inode_newsize_ok(inode, new_size);
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if (ret)
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goto out_mutex;
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- /*
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- * If we have a partial block after EOF we have to allocate
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- * the entire block.
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- */
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- if (partial_end)
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- max_blocks += 1;
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}
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+ flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
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+ if (mode & FALLOC_FL_KEEP_SIZE)
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+ flags |= EXT4_GET_BLOCKS_KEEP_SIZE;
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+
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+ /* Preallocate the range including the unaligned edges */
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+ if (partial_begin || partial_end) {
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+ ret = ext4_alloc_file_blocks(file,
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+ round_down(offset, 1 << blkbits) >> blkbits,
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+ (round_up((offset + len), 1 << blkbits) -
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+ round_down(offset, 1 << blkbits)) >> blkbits,
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+ new_size, flags, mode);
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+ if (ret)
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+ goto out_mutex;
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+
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+ }
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+
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+ /* Zero range excluding the unaligned edges */
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if (max_blocks > 0) {
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+ flags |= (EXT4_GET_BLOCKS_CONVERT_UNWRITTEN |
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+ EXT4_EX_NOCACHE);
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/* Now release the pages and zero block aligned part of pages*/
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truncate_pagecache_range(inode, start, end - 1);
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--
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2.1.0
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