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smb/client: do not account EOF extension as allocation

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cifs_setsize() updates the local inode size after SetEOF succeeds. It also
used the new EOF as a local i_blocks estimate, but extending EOF does not
prove that the intervening range was allocated.

For example, after writing 1 MiB and then extending EOF to 10 MiB, the
client can report the file as fully allocated even though the server still
reports a much smaller AllocationSize:

        $ dd if=/dev/zero of=test bs=1M count=1
        $ truncate -s 10M test && stat -c 'size=%s blocks=%b' test
        $ stat --cached=never -c 'size=%s blocks=%b' test

        client stat:                    size=10485760 blocks=20480
        server stat:                    size=10485760 blocks=2056
        client stat after revalidation: size=10485760 blocks=2056

A later attribute revalidation may correct i_blocks, but callers such as
xfstests generic/495 invoke swapon immediately after truncate. The swapfile
hole check can therefore observe the inflated local i_blocks value and
accept a sparse file.

Do not grow i_blocks from cifs_setsize() on EOF extension.  Only clamp it
on shrink; allocation growth must come from write completion or from
server-reported AllocationSize.

With this change, EOF extension no longer makes a sparse file appear
fully allocated before the next attribute revalidation, and xfstests
generic/495 no longer accepts it through the inflated local i_blocks value.

Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>
This commit is contained in:
Huiwen He
2026-06-24 10:15:46 +08:00
committed by Steve French
parent 2a4b3d2db5
commit 99cd0a6eeb
1 changed files with 10 additions and 3 deletions
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13
fs/smb/client/inode.c
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@@ -3038,13 +3038,20 @@ int cifs_fiemap(struct inode *inode, struct fiemap_extent_info *fei, u64 start,
void cifs_setsize(struct inode *inode, loff_t offset)
{
loff_t old_size;
u64 blocks = CIFS_INO_BLOCKS(offset);
spin_lock(&inode->i_lock);
old_size = i_size_read(inode);
i_size_write(inode, offset);
/*
* Until we can query the server for actual allocation size,
* this is best estimate we have for blocks allocated for a file.
* Extending EOF does not allocate the intervening range. Only clamp
* i_blocks on shrink; allocation growth comes from writes or from the
* server-reported AllocationSize.
*/
inode->i_blocks = CIFS_INO_BLOCKS(offset);
if (offset < old_size && (u64)inode->i_blocks > blocks)
inode->i_blocks = blocks;
spin_unlock(&inode->i_lock);
inode_set_mtime_to_ts(inode, inode_set_ctime_current(inode));
truncate_pagecache(inode, offset);